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篇1

關鍵詞：初中；物理；歐姆定律；教學問題

中圖分類號：G633.7 文(wen)獻標志碼：A 文(wen)章編號：1008-3561（2015）09-0056-01

一、在實驗探(tan)究中讓學(xue)生學(xue)習歐姆定律

歐姆定律是電(dian)(dian)學(xue)(xue)重要內容之(zhi)一，也是中(zhong)考(kao)重點考(kao)查(cha)內容，所以能否教(jiao)好歐姆定律關系到(dao)(dao)之(zhi)后對中(zhong)考(kao)的(de)(de)(de)重點知(zhi)識(shi)復習(xi)，更有(you)可(ke)能影響學(xue)(xue)生對于物(wu)理學(xue)(xue)的(de)(de)(de)熱情。在實驗探究的(de)(de)(de)過(guo)程之(zhi)中(zhong)以學(xue)(xue)生為主，教(jiao)師(shi)起引導(dao)作用(yong)，讓學(xue)(xue)生通過(guo)觀察電(dian)(dian)壓表(biao)、電(dian)(dian)流表(biao)、滑動變阻器的(de)(de)(de)微量(liang)變化(hua)發現(xian)問(wen)(wen)題(ti)、提(ti)出問(wen)(wen)題(ti)，他(ta)們(men)對于自己發現(xian)的(de)(de)(de)問(wen)(wen)題(ti)會比老師(shi)直接(jie)教(jiao)導(dao)的(de)(de)(de)印(yin)象深(shen)刻，從而(er)達(da)到(dao)(dao)了教(jiao)學(xue)(xue)目的(de)(de)(de)。

二(er)、在歐姆(mu)定律的學習中(zhong)最經常遇到的問題

在實際的(de)(de)(de)(de)(de)教學(xue)之中，教師要把電(dian)(dian)路(lu)(lu)的(de)(de)(de)(de)(de)認識與畫電(dian)(dian)路(lu)(lu)圖(tu)、連接電(dian)(dian)路(lu)(lu)作為(wei)主要的(de)(de)(de)(de)(de)教學(xue)任務，開闊學(xue)生(sheng)的(de)(de)(de)(de)(de)思維(wei)，加強對電(dian)(dian)路(lu)(lu)的(de)(de)(de)(de)(de)認識。物理(li)是(shi)(shi)一門比較枯(ku)燥的(de)(de)(de)(de)(de)課程，只有激發學(xue)生(sheng)的(de)(de)(de)(de)(de)熱情，才能更好地完成授課。電(dian)(dian)流(liu)(liu)、電(dian)(dian)壓(ya)、電(dian)(dian)阻(zu)(zu)的(de)(de)(de)(de)(de)概(gai)念(nian)及單位，電(dian)(dian)流(liu)(liu)表、電(dian)(dian)壓(ya)表、滑動變(bian)(bian)阻(zu)(zu)器(qi)的(de)(de)(de)(de)(de)使用，是(shi)(shi)最基(ji)(ji)礎(chu)的(de)(de)(de)(de)(de)概(gai)念(nian)。電(dian)(dian)流(liu)(liu)表測(ce)量電(dian)(dian)流(liu)(liu)、電(dian)(dian)壓(ya)表測(ce)量電(dian)(dian)壓(ya)、變(bian)(bian)阻(zu)(zu)器(qi)調節電(dian)(dian)路(lu)(lu)中的(de)(de)(de)(de)(de)電(dian)(dian)流(liu)(liu)，這部分則比較重要，需要重點講解(jie)。電(dian)(dian)流(liu)(liu)、電(dian)(dian)壓(ya)、電(dian)(dian)阻(zu)(zu)的(de)(de)(de)(de)(de)概(gai)念(nian)是(shi)(shi)基(ji)(ji)本的(de)(de)(de)(de)(de)電(dian)(dian)學(xue)測(ce)量儀器(qi)，明確這些(xie)儀器(qi)的(de)(de)(de)(de)(de)使用與操作，是(shi)(shi)非(fei)常重要的(de)(de)(de)(de)(de)，關系到后期實驗的(de)(de)(de)(de)(de)正(zheng)確性與對知識的(de)(de)(de)(de)(de)理(li)解(jie)。以上基(ji)(ji)礎(chu)知識的(de)(de)(de)(de)(de)理(li)解(jie)與運用又是(shi)(shi)進一步(bu)學(xue)習歐姆(mu)定律的(de)(de)(de)(de)(de)基(ji)(ji)礎(chu)。

三、歐(ou)姆(mu)定律(lv)的(de)(de)主要內容是電流、電壓(ya)、電阻(zu)的(de)(de)關系

這部分知(zhi)識(shi)是(shi)在實驗的(de)(de)(de)基(ji)礎上概(gai)括、歸納(na)出了(le)電(dian)路中(zhong)電(dian)壓、電(dian)流(liu)(liu)、電(dian)阻三(san)者相互關聯的(de)(de)(de)關系。教師在實驗中(zhong)要讓(rang)(rang)學(xue)生理(li)(li)解電(dian)流(liu)(liu)隨(sui)電(dian)壓和電(dian)阻的(de)(de)(de)變化(hua)而變化(hua)，對于(yu)多個變量問題的(de)(de)(de)研究是(shi)采用(yong)(yong)固定一個量不變，研究其余兩個量的(de)(de)(de)變化(hua)的(de)(de)(de)處理(li)(li)方法(fa)，從而讓(rang)(rang)學(xue)生學(xue)會物理(li)(li)學(xue)中(zhong)常用(yong)(yong)這種方法(fa)。歐(ou)姆定律(lv)(lv)在初中(zhong)只講部分電(dian)路的(de)(de)(de)歐(ou)姆定律(lv)(lv)，是(shi)電(dian)學(xue)中(zhong)的(de)(de)(de)基(ji)本定律(lv)(lv)，是(shi)進一步學(xue)習電(dian)學(xue)知(zhi)識(shi)分析和進行電(dian)路計(ji)算(suan)的(de)(de)(de)基(ji)礎，是(shi)初中(zhong)電(dian)學(xue)的(de)(de)(de)重(zhong)點知(zhi)識(shi)。

歐姆定律是初中物理學電學的重點、也是難點，想要研究歐姆(mu)定律(lv)必須要建立電流(liu)、電壓、電阻(zu)的(de)關系，并在實(shi)驗(yan)的(de)基(ji)礎上(shang)得出歐姆(mu)定律(lv)，做好(hao)演示實(shi)驗(yan)，歸納、分析、概括(kuo)實(shi)驗(yan)結果，使(shi)學(xue)生(sheng)正(zheng)確理解歐姆(mu)定律(lv)的(de)基(ji)礎。所(suo)以，使(shi)用電流(liu)表、電壓表、滑動變阻(zu)器是這部(bu)分知(zhi)識中的(de)重點實(shi)驗(yan)的(de)基(ji)礎。

電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)、電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)(ya)、電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻的(de)(de)(de)(de)(de)(de)(de)(de)概(gai)念(nian)是(shi)(shi)學(xue)生(sheng)學(xue)習的(de)(de)(de)(de)(de)(de)(de)(de)難點，由(you)于(yu)初中學(xue)生(sheng)水(shui)平有(you)限(xian)，對電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)、電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)(ya)的(de)(de)(de)(de)(de)(de)(de)(de)概(gai)念(nian)要求較低(di)，并(bing)沒有(you)下準確的(de)(de)(de)(de)(de)(de)(de)(de)定(ding)(ding)義。因此，電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻的(de)(de)(de)(de)(de)(de)(de)(de)概(gai)念(nian)就成(cheng)(cheng)了學(xue)生(sheng)理(li)解(jie)的(de)(de)(de)(de)(de)(de)(de)(de)難點。教師要多舉例(li)子幫助學(xue)生(sheng)理(li)解(jie)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻是(shi)(shi)導體本身(shen)的(de)(de)(de)(de)(de)(de)(de)(de)屬性，決定(ding)(ding)于(yu)導體的(de)(de)(de)(de)(de)(de)(de)(de)材(cai)料、長度、橫截面和溫度，它用兩端(duan)的(de)(de)(de)(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)(ya)和通(tong)過(guo)的(de)(de)(de)(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)的(de)(de)(de)(de)(de)(de)(de)(de)比值來(lai)(lai)表(biao)(biao)(biao)示(shi)是(shi)(shi)為了測量(liang)(liang)的(de)(de)(de)(de)(de)(de)(de)(de)方(fang)便，與(yu)外加(jia)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)(ya)、電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)無關。同時(shi)，教師一定(ding)(ding)要糾正(zheng)一些學(xue)生(sheng)經常出現的(de)(de)(de)(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻隨(sui)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)(ya)、電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)的(de)(de)(de)(de)(de)(de)(de)(de)變(bian)化(hua)而(er)變(bian)化(hua)的(de)(de)(de)(de)(de)(de)(de)(de)錯誤(wu)概(gai)念(nian)，也(ye)就是(shi)(shi)對歐姆(mu)定(ding)(ding)律(lv)的(de)(de)(de)(de)(de)(de)(de)(de)錯誤(wu)理(li)解(jie)。歐姆(mu)定(ding)(ding)律(lv)在學(xue)生(sheng)頭腦的(de)(de)(de)(de)(de)(de)(de)(de)建立過(guo)程(cheng)是(shi)(shi)十分重要的(de)(de)(de)(de)(de)(de)(de)(de)，認真(zhen)做好演示(shi)實驗(yan)，用實驗(yan)來(lai)(lai)探索(suo)一個(ge)量(liang)(liang)隨(sui)兩個(ge)量(liang)(liang)變(bian)化(hua)的(de)(de)(de)(de)(de)(de)(de)(de)定(ding)(ding)量(liang)(liang)關系(xi)(xi)是(shi)(shi)第一次。首先要向(xiang)(xiang)學(xue)生(sheng)交代清楚實驗(yan)的(de)(de)(de)(de)(de)(de)(de)(de)研(yan)究(jiu)方(fang)法，本實驗(yan)彩(cai)用控(kong)制變(bian)量(liang)(liang)法來(lai)(lai)研(yan)究(jiu)，即“固定(ding)(ding)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻不(bu)變(bian)，研(yan)究(jiu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)跟(gen)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)(ya)的(de)(de)(de)(de)(de)(de)(de)(de)關系(xi)(xi)；固定(ding)(ding)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)(ya)不(bu)變(bian)，研(yan)究(jiu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)跟(gen)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻的(de)(de)(de)(de)(de)(de)(de)(de)關系(xi)(xi)”。在連接(jie)(jie)如(ru)圖（圖略）所示(shi)的(de)(de)(de)(de)(de)(de)(de)(de)實驗(yan)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)路時(shi)，要將具體接(jie)(jie)法演示(shi)給學(xue)生(sheng)看。可以先從電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源正(zheng)極開始(shi)，按電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)方(fang)向(xiang)(xiang)依次為電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)、開關S、滑動變(bian)阻器R′、定(ding)(ding)值電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻R、電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)表(biao)(biao)(biao)串(chuan)聯(lian)(lian)(lian)起來(lai)(lai)組成(cheng)(cheng)一個(ge)閉合回路，最后將電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)(ya)表(biao)(biao)(biao)并(bing)聯(lian)(lian)(lian)在定(ding)(ding)值電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻R兩端(duan)。同時(shi)提醒學(xue)生(sheng)注(zhu)意(yi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)必須(xu)從電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)表(biao)(biao)(biao)和電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)(ya)表(biao)(biao)(biao)的(de)(de)(de)(de)(de)(de)(de)(de)正(zheng)接(jie)(jie)線(xian)柱流(liu)(liu)進電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)表(biao)(biao)(biao)，負接(jie)(jie)線(xian)柱流(liu)(liu)出電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)表(biao)(biao)(biao)及量(liang)(liang)程(cheng)選擇，電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)表(biao)(biao)(biao)與(yu)R串(chuan)聯(lian)(lian)(lian)，其示(shi)數(shu)等于(yu)通(tong)過(guo)R的(de)(de)(de)(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)。電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)(ya)表(biao)(biao)(biao)與(yu)R并(bing)聯(lian)(lian)(lian)其數(shu)等于(yu)R兩端(duan)的(de)(de)(de)(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)(ya)。

運用歐姆定律(lv)可以推導(dao)串聯(lian)電路中的總電阻跟各串聯(lian)電阻之間的關系及(ji)電壓分配跟導(dao)體(ti)電阻的關系，具(ju)體(ti)推導(dao)如下：

在串(chuan)聯電(dian)路(lu)中：I=I1=I2；U=U1+U2；由歐姆定(ding)律公(gong)式I=U/R，可(ke)得(de)U=IR；U1=I1R1；U2=I2R2將這些式子代入上式得(de)：IR=I1R1+I2R2即R=R1+R2；也就是說串(chuan)聯電(dian)路(lu)的總電(dian)阻等于各串(chuan)聯導體的電(dian)阻之和。

在串(chuan)聯(lian)(lian)電(dian)(dian)路中(zhong)：I=I1=I2；由歐姆定律公式(shi)I=U/R，可得：I1=U1/R1；I2=U2/R2；將這些式(shi)子(zi)代入上式(shi)得：U1/R2=U2/R2 變換一下形式(shi)得：U1/U2=R1/R2；即串(chuan)聯(lian)(lian)電(dian)(dian)路中(zhong)，電(dian)(dian)壓分配跟導體電(dian)(dian)阻成正比。

四、結束語

通過(guo)對物理教(jiao)(jiao)學內容的(de)分析(xi)、思(si)(si)維(wei)方法(fa)、能力(li)(li)(li)訓練(lian)的(de)具(ju)體研(yan)究(jiu)，對教(jiao)(jiao)學內容進行歸(gui)(gui)納(na)總(zong)結，可以使初中物理教(jiao)(jiao)師掌(zhang)握(wo)歐姆定律的(de)基本理論(lun)方法(fa)，更(geng)好地駕駛物理教(jiao)(jiao)材(cai)，提高(gao)物理教(jiao)(jiao)學質量(liang)，把(ba)重(zhong)點(dian)真正(zheng)落實(shi)(shi)(shi)在(zai)教(jiao)(jiao)學過(guo)程中，幫助學生(sheng)提高(gao)實(shi)(shi)(shi)驗操作能力(li)(li)(li)、歸(gui)(gui)納(na)概括能力(li)(li)(li)、演繹推理能力(li)(li)(li)、邏輯推理能力(li)(li)(li)、抽象思(si)(si)維(wei)能力(li)(li)(li)及靈活(huo)運用知識(shi)解決(jue)問題(ti)的(de)能力(li)(li)(li)，讓學生(sheng)學會控(kong)制變(bian)量(liang)法(fa)研(yan)究(jiu)多個變(bian)量(liang)的(de)問題(ti)，學會用等效法(fa)分析(xi)復雜(za)電路。因(yin)此，教(jiao)(jiao)師要注(zhu)重(zhong)培養學生(sheng)實(shi)(shi)(shi)事(shi)求(qiu)是的(de)科學態(tai)度(du)，從而有效培養學生(sheng)的(de)物理素質。

參考文獻：

篇2

課(ke)題：閉合(he)電(dian)路(lu)的歐(ou)姆定律（第一課(ke)時）

課型：復習課

【教學目標】

一、 知識目標

1. 理解閉合電(dian)路(lu)(lu)的歐姆定律，并(bing)用(yong)它進行有關電(dian)路(lu)(lu)問(wen)題的分析和計(ji)算.

2. 理解路端電壓與(yu)負載的關系.

二、 能力目標

1. 通過對(dui)U-I圖(tu)線(xian)的(de)分析培養學生應用(yong)數(shu)學工(gong)具(ju)解決物理問題(ti)的(de)能(neng)力.

2. 利(li)用(yong)閉合(he)電路歐姆(mu)定(ding)律解決一些簡(jian)單的實(shi)際(ji)問題(ti)(ti)，培養學生運用(yong)物理知識解決實(shi)際(ji)問題(ti)(ti)的能力.

三、 情感目標

通過(guo)本(ben)節課教(jiao)學(xue)，加(jia)強(qiang)對學(xue)生科學(xue)素質(zhi)的培(pei)養，通過(guo)探究(jiu)物理(li)規律(lv)培(pei)養學(xue)生創新精神和實踐能(neng)力.

【教學重難點】

1. 閉(bi)合電路的歐姆(mu)定律(lv)

2. 路端電壓與電流（外電阻）關系的公式表(biao)示法及(ji)圖線表(biao)示法.

【考點再現(xian) 設疑(yi)激思】

一、 電動勢

1. 電(dian)源是通過非靜電(dian)力做功(gong)把 的(de)(de)能轉化成 的(de)(de)裝置.

2. 電(dian)動勢：非靜電(dian)力(li)搬(ban)運電(dian)荷所(suo)做的功跟搬(ban)運的電(dian)荷電(dian)量的比值，E= ，

單位：V .

3.電(dian)動(dong)勢的物理含義：電(dian)動(dong)勢表示電(dian)源 本(ben)領的大小，在數值上等于電(dian)源沒(mei)有接入(ru)電(dian)路(lu)時兩極間的電(dian)壓(ya).

電(dian)動勢與電(dian)壓(ya)有什么區別？

（1、其它形式(shi)、電能(neng) 2、 Wq 3、將(jiang)其它形式(shi)的(de)轉化為電能(neng)）

（電動(dong)勢反映其它形(xing)式的能轉化為(wei)電能的本領，電壓形(xing)成電場，促(cu)使電流(liu)做功.）

二(er)、閉(bi)合電路歐姆定律

1.定律內容：閉合電(dian)(dian)(dian)路的電(dian)(dian)(dian)流跟電(dian)(dian)(dian)源(yuan)電(dian)(dian)(dian)動勢成 ， 跟內、外電(dian)(dian)(dian)路的電(dian)(dian)(dian)阻之(zhi)和成 .

2.定律表達式(shi)為I=

3.適用條件

4.閉合電路歐姆定律的兩種常用關(guan)系式(shi)：

（1）E=

（2）E=

你認(ren)為(wei)電源的(de)(de)內阻是恒定的(de)(de)還是不斷變化？定律表(biao)達(da)式怎(zen)樣(yang)推導出來的(de)(de)？

電(dian)(dian)路中電(dian)(dian)流(liu)一定從(cong)高電(dian)(dian)勢(shi)流(liu)向(xiang)低(di)電(dian)(dian)勢(shi)，對嗎？

（1、正比、反比；2、I=ER+r； 3.純電(dian)阻電(dian)路；4.E=U內+U外、E=U外+Ir）

（電(dian)(dian)源內阻短時間可認(ren)為不變、定(ding)律從(cong)能(neng)量守(shou)恒推導、不對，內電(dian)(dian)路電(dian)(dian)流方向(xiang)從(cong)低電(dian)(dian)勢流向(xiang)高電(dian)(dian)勢）

三、路端電壓(ya)U與(yu)外電阻R的關系

根據(ju)U= 知，當外(wai)電(dian)(dian)(dian)(dian)路(lu)電(dian)(dian)(dian)(dian)阻R增大(da)時(shi)，電(dian)(dian)(dian)(dian)路(lu)的總電(dian)(dian)(dian)(dian)流I ，電(dian)(dian)(dian)(dian)源內電(dian)(dian)(dian)(dian)壓U內 ，路(lu)端電(dian)(dian)(dian)(dian)壓U外(wai) .

（E-Ir 、減小、減小、增大(da)）

四、U-I關系圖

由U= 可知，路端電(dian)壓隨著電(dian)路中電(dian)流的增大而(er)內(nei)電(dian)壓 ；

1.當電路斷(duan)路即I=0時，縱坐標的截距為 .

2.當外電路(lu)電壓為U=0時，橫坐標的截距(ju)為 .

3.圖(tu)線的(de)斜(xie)率的(de)絕對值為電(dian)源的(de) .

注意點：縱(zong)軸起點是(shi)否(fou)為零.

電源的(de)U-I關系圖與電阻的(de)U-I關系圖有什么不同？

（E-Ir、減小 1.E 2.I短 3.r）

（電(dian)(dian)(dian)(dian)源的U-I關(guan)(guan)(guan)系(xi)(xi)圖反(fan)映路端電(dian)(dian)(dian)(dian)壓與電(dian)(dian)(dian)(dian)流關(guan)(guan)(guan)系(xi)(xi)、電(dian)(dian)(dian)(dian)阻的U-I關(guan)(guan)(guan)系(xi)(xi)圖反(fan)映電(dian)(dian)(dian)(dian)阻兩端電(dian)(dian)(dian)(dian)壓與通過它(ta)的電(dian)(dian)(dian)(dian)流關(guan)(guan)(guan)系(xi)(xi)）

五、電源的功率

1.電源的總功(gong)率P總= .

2.電源(yuan)的(de)輸出功率P出=.

（1.EI 2.UI）

考(kao)(kao)點(dian)說明： 閉合電路歐姆定律是二級要求，常在選擇題(ti)中(zhong)出現(xian)動態電路分析，實驗(yan)中(zhong)常考(kao)(kao)查(cha)U-I圖(tu)線的有關知識(shi)點(dian).

復習考點還須引導學生多(duo)閱讀教(jiao)材(cai)，多(duo)思考，多(duo)歸(gui)納總結(jie)，多(duo)聯系實際.

【典型(xing)例題剖析 學會歸納總結】

題型(xing)1閉(bi)合電路歐姆定律(lv)的(de)動態(tai)分析

例1 如圖所示，電源(yuan)電動勢E=12 V，內阻r=1 Ω，R1=5 Ω，R2=12 Ω，R3的最(zui)大阻值為6 Ω.

（1）求(qiu)：流過電流表的最小電流？

（2）若R3的阻值減小，其它元件均(jun)不(bu)變，判(pan)斷電路(lu)中電壓表(biao)、電流表(biao)的示數如何變化？

答案：（1）0.8A；（2）V1、V2減小(xiao)A增大

方(fang)法(fa)點撥：支(zhi)路-干路-支(zhi)路

學生的(de)疑點：1.總電阻的(de)變化不清；

2.內電壓變(bian)化忘了(le)分析；

3.路(lu)、支路(lu)，電(dian)壓(ya)、電(dian)流變(bian)換搞昏(hun)了頭.

【當堂鞏固1】

如圖所示，電源電動勢E=8 V，內阻不為(wei)零(ling)，電燈A標(biao)有(you)(you)“10 V，10 W”字樣，電燈B標(biao)有(you)(you)“8 V 20 W”字樣，滑動變阻器的(de)(de)總電阻為(wei)6 Ω.閉合開(kai)關S，當(dang)滑動觸頭P由a端向b端滑動的(de)(de)過程中（不考(kao)慮電燈電阻的(de)(de)變化） （ A ）

A.電流表的示(shi)數(shu)一直增(zeng)大，電壓表的示(shi)數(shu)一直減小(xiao)

B.電流(liu)表的(de)示數一直減小(xiao)，電壓表的(de)示數一直增大

C.電流(liu)表的(de)示數(shu)先增大(da)后減小，電壓表的(de)示數(shu)先減小后增大(da)

D.電(dian)流表(biao)的示數先減小(xiao)后增大(da)，電(dian)壓(ya)表(biao)的示數先增大(da)后減小(xiao)

探究：P移動電(dian)路總電(dian)阻怎樣變化？

題型2探究(jiu)含電容(rong)電路的判斷與計算

例2 如圖所示，E=10 V，r=1 Ω，R1=R3=5 Ω，R2=4 Ω， C=100 F，當(dang)S斷開(kai)時，電容器(qi)中帶電粒(li)子恰好處于靜止狀態.求：

（1）S閉合后，帶(dai)電(dian)粒(li)子加速度的大小和(he)方向(xiang).

（2）S閉合后流過(guo)R3的(de)總電荷量.

答案：（1）10 m/s2向上(shang)；（2）400 C

方法(fa)點撥 電容器兩(liang)極(ji)電壓(ya)與R2兩(liang)端電壓(ya)關系？R3在電路中有什么作(zuo)用？

學生疑點：1.電容兩端電壓(ya)變(bian)化沒搞清；

2.與電容串(chuan)聯的電阻作用不明；

3.電路結構(gou)認識不清.

【當堂鞏固2】

如圖電路中，當(dang)滑動(dong)變阻器的(de)觸頭P向上滑動(dong)時(shi)，則(ze) （ D ）

A.電源的總功率變小(xiao)

B.電容器貯存(cun)的電荷量變大

C.燈L1變暗

D.燈L2變亮

題(ti)型3 探(tan)究 U-I圖象的應用(yong)

 例3 如(ru)圖所示，直(zhi)線A為(wei)電(dian)源(yuan)(yuan)的(de)路端電(dian)壓U與(yu)電(dian)流(liu)I的(de)關系圖象，直(zhi)線B是電(dian)阻(zu)R的(de)兩端電(dian)壓與(yu)通過其電(dian)流(liu)I的(de)關系圖象，用該電(dian)源(yuan)(yuan)與(yu)電(dian)阻(zu)R組成(cheng)閉合電(dian)路，則(ze)電(dian)源(yuan)(yuan)的(de)總(zong)功率(lv)(lv)為(wei) W，電(dian)源(yuan)(yuan)的(de)輸出功率(lv)(lv)為(wei) W電(dian)源(yuan)(yuan)的(de)效率(lv)(lv)為(wei)

.

答(da)案：6 W 4 W 23

探究：圖(tu)線的交點有什么(me)物理意義？（工作點）

【當堂鞏固3】

如圖所示(shi)，為一個電燈兩端的(de)(de)電壓(ya)與通過(guo)它(ta)的(de)(de)電流(liu)(liu)的(de)(de)變(bian)(bian)化關(guan)(guan)系曲(qu)線.由(you)(you)圖可知(zhi)，兩者不成(cheng)線性(xing)關(guan)(guan)系，這是(shi)由(you)(you)于焦耳(er)熱使燈絲的(de)(de)溫度(du)發生了變(bian)(bian)化的(de)(de)緣故.參考這條曲(qu)線探(tan)究下列問題（不計電流(liu)(liu)表的(de)(de)內阻）.

（1） 若把一個(ge)這樣的(de)電(dian)燈(deng)(deng)串聯，接到電(dian)動(dong)勢為6 V，內阻為10 Ω的(de)電(dian)源上(shang)，如圖甲所示求(qiu)流(liu)過燈(deng)(deng)泡的(de)電(dian)流(liu)和燈(deng)(deng)泡的(de)電(dian)阻？

（2） 若將(jiang)兩個這樣(yang)的電(dian)燈并(bing)聯后接在這個電(dian)源上，如圖乙所示(shi)，則通過電(dian)流(liu)(liu)表的電(dian)流(liu)(liu)值(zhi)和(he)每個燈泡的電(dian)阻？

方(fang)法點撥：寫出(chu)U=E-Ir其中I為通過電(dian)源(yuan)的電(dian)流，并作圖(tu)找(zhao)交點.

答案(an)：（1）0.35 A 7.1Ω （2）0.24 A 17.5Ω（提(ti)示寫出U=E-2Ir其中2I為通過(guo)電源的電流，并(bing)作圖找(zhao)交點）

學生難點：

1.圖像特別(bie)是曲線，不會找具體信息；

2.對電(dian)阻與(yu)電(dian)源的U-I圖象(xiang)的區別不清楚；

篇3

關鍵詞：電(dian)阻測量；設計性(xing)實驗(yan)；物理

物理是以(yi)實(shi)(shi)驗(yan)(yan)為(wei)基(ji)礎的(de)(de)學科，不論是理科綜合(he)能力測(ce)試還是單學科的(de)(de)高(gao)考(kao)，都(dou)十分重視(shi)實(shi)(shi)驗(yan)(yan)能力的(de)(de)考(kao)查。近年來高(gao)考(kao)物理中的(de)(de)實(shi)(shi)驗(yan)(yan)題(ti)已從側重于考(kao)查實(shi)(shi)驗(yan)(yan)的(de)(de)原理、器(qi)材選擇、步驟、數據處理、得(de)出結論、誤差的(de)(de)定性原因等(deng)即考(kao)查實(shi)(shi)驗(yan)(yan)儀器(qi)的(de)(de)使用、基(ji)本操作(zuo)等(deng)最基(ji)礎的(de)(de)實(shi)(shi)驗(yan)(yan)能力，向著更側重于考(kao)查對實(shi)(shi)驗(yan)(yan)原理的(de)(de)理解、實(shi)(shi)驗(yan)(yan)方法的(de)(de)靈活(huo)運用等(deng)更高(gao)層次(ci)的(de)(de)能力要求(qiu)轉變，從常見的(de)(de)學生(sheng)分組(zu)實(shi)(shi)驗(yan)(yan)、演(yan)示實(shi)(shi)驗(yan)(yan)及課(ke)后(hou)小實(shi)(shi)驗(yan)(yan)的(de)(de)考(kao)查向更高(gao)層次(ci)的(de)(de)設計性實(shi)(shi)驗(yan)(yan)考(kao)查過渡。高(gao)考(kao)實(shi)(shi)驗(yan)(yan)題(ti)的(de)(de)設計性實(shi)(shi)驗(yan)(yan)常見于電學實(shi)(shi)驗(yan)(yan)中，而(er)電阻測(ce)量的(de)(de)設計性實(shi)(shi)驗(yan)(yan)更是其重點、熱(re)點，對學生(sheng)而(er)言當然(ran)也是難點。本文(wen)擬就如何(he)突破(po)這(zhe)一難點做些(xie)討論．

一(yi)、千變(bian)萬(wan)變(bian)，原(yuan)理(li)不變(bian)

縱觀近幾年高考(kao)中的(de)(de)電(dian)阻測(ce)量(liang)設(she)計(ji)(ji)性(xing)實(shi)(shi)(shi)(shi)驗(yan)(yan)(yan)(yan)題(ti)目(mu)(mu)，立(li)(li)意新穎(ying)、靈(ling)活(huo)多(duo)變。為了(le)應(ying)對這(zhe)種實(shi)(shi)(shi)(shi)驗(yan)(yan)(yan)(yan)，總結了(le)不(bu)少方法(fa)(fa)，如“伏伏法(fa)(fa)”、“安安法(fa)(fa)”，名目(mu)(mu)繁多(duo)，不(bu)一(yi)而足(zu)。其(qi)實(shi)(shi)(shi)(shi)不(bu)論(lun)題(ti)目(mu)(mu)多(duo)么新穎(ying)，不(bu)論(lun)怎么變化，須知萬變不(bu)離其(qi)宗(zong)，這(zhe)個“宗(zong)”就是(shi)實(shi)(shi)(shi)(shi)驗(yan)(yan)(yan)(yan)原(yuan)理(li)(li)。原(yuan)理(li)(li)是(shi)實(shi)(shi)(shi)(shi)驗(yan)(yan)(yan)(yan)的(de)(de)總綱(gang)、靈(ling)魂，設(she)計(ji)(ji)性(xing)實(shi)(shi)(shi)(shi)驗(yan)(yan)(yan)(yan)也概莫(mo)能(neng)外。高考(kao)理(li)(li)科綜合能(neng)力測(ce)試(shi)《考(kao)試(shi)大綱(gang)》對設(she)計(ji)(ji)性(xing)實(shi)(shi)(shi)(shi)驗(yan)(yan)(yan)(yan)題(ti)目(mu)(mu)的(de)(de)考(kao)查有具體明確的(de)(de)要求：“能(neng)靈(ling)活(huo)地運用已學(xue)(xue)過的(de)(de)物理(li)(li)理(li)(li)論(lun)、實(shi)(shi)(shi)(shi)驗(yan)(yan)(yan)(yan)方法(fa)(fa)和(he)實(shi)(shi)(shi)(shi)驗(yan)(yan)(yan)(yan)儀(yi)器去處理(li)(li)問題(ti)”。設(she)計(ji)(ji)性(xing)實(shi)(shi)(shi)(shi)驗(yan)(yan)(yan)(yan)考(kao)題(ti)都是(shi)根據現行教學(xue)(xue)大綱(gang)和(he)考(kao)試(shi)大綱(gang)，立(li)(li)足(zu)于課本，在已學(xue)(xue)實(shi)(shi)(shi)(shi)驗(yan)(yan)(yan)(yan)（包(bao)括學(xue)(xue)生(sheng)分(fen)(fen)組(zu)實(shi)(shi)(shi)(shi)驗(yan)(yan)(yan)(yan)、演示實(shi)(shi)(shi)(shi)驗(yan)(yan)(yan)(yan)及課后小實(shi)(shi)(shi)(shi)驗(yan)(yan)(yan)(yan)）的(de)(de)基礎上(shang)演變而來(lai)的(de)(de)，是(shi)建立(li)(li)在對所學(xue)(xue)實(shi)(shi)(shi)(shi)驗(yan)(yan)(yan)(yan)原(yuan)理(li)(li)的(de)(de)深入理(li)(li)解的(de)(de)基礎上(shang)的(de)(de)。具體到電(dian)阻的(de)(de)測(ce)量(liang)，其(qi)實(shi)(shi)(shi)(shi)驗(yan)(yan)(yan)(yan)原(yuan)理(li)(li)最主要的(de)(de)應(ying)是(shi)兩個，一(yi)是(shi)部分(fen)(fen)電(dian)路歐姆定(ding)律(lv)（即(ji)所謂伏安法(fa)(fa)），二是(shi)閉(bi)合電(dian)路歐姆定(ding)律(lv)，茲(zi)分(fen)(fen)述于后：

⑴伏安法。設待測(ce)電(dian)(dian)阻(zu)阻(zu)值(zhi)為Rx．若(ruo)測(ce)得Rx兩(liang)端的電(dian)(dian)壓為U，通過Rx的電(dian)(dian)流(liu)為I，則由(you)其定義(yi)可得Rx＝U/I。此處應注意“測(ce)”的含義(yi)，例如(ru)，電(dian)(dian)壓U既(ji)可用電(dian)(dian)壓表直接測(ce)得，也可由(you)其他方式算出即間接測(ce)得。電(dian)(dian)流(liu)亦然。

⑵閉(bi)合電路歐(ou)姆定律。將待(dai)測電阻Rx做為(wei)某一電源的(de)外電路或外電路的(de)一部分(fen)，利用閉(bi)合電路歐(ou)姆定律測量，這(zhe)當然也是間接測得的(de)。

二、方案選擇(ze)，應看條件(jian)

電(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)測(ce)(ce)量設計性實(shi)(shi)驗(yan)(yan)之所以(yi)難，對(dui)(dui)很(hen)多學生來說(shuo)，不(bu)是(shi)(shi)(shi)(shi)不(bu)知(zhi)道有(you)哪些(xie)實(shi)(shi)驗(yan)(yan)原理(li)，而是(shi)(shi)(shi)(shi)不(bu)清楚對(dui)(dui)一(yi)(yi)個(ge)具體(ti)的(de)(de)(de)(de)實(shi)(shi)驗(yan)(yan)應(ying)(ying)該用(yong)哪個(ge)原理(li)。實(shi)(shi)際(ji)上，在一(yi)(yi)道具體(ti)的(de)(de)(de)(de)實(shi)(shi)驗(yan)(yan)題(ti)(ti)目(mu)中(zhong)(zhong)實(shi)(shi)驗(yan)(yan)原理(li)的(de)(de)(de)(de)選擇受實(shi)(shi)驗(yan)(yan)器(qi)材、實(shi)(shi)驗(yan)(yan)精度的(de)(de)(de)(de)要(yao)求等多種因(yin)素的(de)(de)(de)(de)制約(yue)。如考慮(lv)(lv)用(yong)伏安(an)法(fa)(fa)測(ce)(ce)電(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)時，一(yi)(yi)般而言應(ying)(ying)有(you)電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)表(biao)(biao)(biao)、電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)表(biao)(biao)(biao)。若(ruo)只(zhi)有(you)兩(liang)(liang)個(ge)電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)表(biao)(biao)(biao)，沒有(you)電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)表(biao)(biao)(biao)，并(bing)不(bu)意(yi)(yi)味著無法(fa)(fa)用(yong)伏安(an)法(fa)(fa)。只(zhi)要(yao)滿足一(yi)(yi)定(ding)(ding)條(tiao)件(jian)，實(shi)(shi)驗(yan)(yan)仍然能夠(gou)完成。前面說(shuo)過(guo)(guo)，只(zhi)要(yao)能算出(chu)(chu)待(dai)測(ce)(ce)電(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)兩(liang)(liang)端(duan)的(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)即可。在什么情況(kuang)下可以(yi)“算出(chu)(chu)”？這(zhe)就需要(yao)注意(yi)(yi)電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)表(biao)(biao)(biao)、電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)表(biao)(biao)(biao)的(de)(de)(de)(de)一(yi)(yi)些(xie)指(zhi)標。一(yi)(yi)般來說(shuo)，電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)（流(liu)(liu)）表(biao)(biao)(biao)應(ying)(ying)看三(san)(san)個(ge)指(zhi)標即滿偏電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)、滿偏電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)和內(nei)(nei)阻(zu)(zu)(zu)(zu)，由(you)于電(dian)(dian)(dian)(dian)(dian)表(biao)(biao)(biao)此(ci)(ci)時滿足部(bu)分電(dian)(dian)(dian)(dian)(dian)路(lu)歐姆定(ding)(ding)律，故(gu)三(san)(san)個(ge)指(zhi)標中(zhong)(zhong)只(zhi)有(you)兩(liang)(liang)個(ge)是(shi)(shi)(shi)(shi)獨(du)立的(de)(de)(de)(de)，利用(yong)任意(yi)(yi)兩(liang)(liang)個(ge)指(zhi)標可由(you)歐姆定(ding)(ding)律求出(chu)(chu)第三(san)(san)個(ge)指(zhi)標。這(zhe)也說(shuo)明(ming)電(dian)(dian)(dian)(dian)(dian)表(biao)(biao)(biao)可扮(ban)演(yan)三(san)(san)種角色，例(li)如一(yi)(yi)個(ge)電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)表(biao)(biao)(biao)，既是(shi)(shi)(shi)(shi)一(yi)(yi)個(ge)電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)表(biao)(biao)(biao)（測(ce)(ce)內(nei)(nei)阻(zu)(zu)(zu)(zu)RV兩(liang)(liang)端(duan)的(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)），又是(shi)(shi)(shi)(shi)一(yi)(yi)個(ge)定(ding)(ding)值電(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)（阻(zu)(zu)(zu)(zu)值為(wei)內(nei)(nei)阻(zu)(zu)(zu)(zu)RV），同時還(huan)能反(fan)串(chuan)電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)表(biao)(biao)(biao)（“測(ce)(ce)”通過(guo)(guo)RV的(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)）．能否(fou)“測(ce)(ce)出(chu)(chu)”通過(guo)(guo)RV的(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)，就取決(jue)于其(qi)(qi)內(nei)(nei)阻(zu)(zu)(zu)(zu)是(shi)(shi)(shi)(shi)否(fou)已知(zhi)。故(gu)若(ruo)題(ti)(ti)目(mu)明(ming)確說(shuo)明(ming)其(qi)(qi)電(dian)(dian)(dian)(dian)(dian)表(biao)(biao)(biao)的(de)(de)(de)(de)內(nei)(nei)阻(zu)(zu)(zu)(zu)是(shi)(shi)(shi)(shi)多少，則可考慮(lv)(lv)讓此(ci)(ci)電(dian)(dian)(dian)(dian)(dian)表(biao)(biao)(biao)反(fan)串(chuan)另一(yi)(yi)種電(dian)(dian)(dian)(dian)(dian)表(biao)(biao)(biao)的(de)(de)(de)(de)角色（當(dang)然，可能還(huan)須考慮(lv)(lv)其(qi)(qi)偏轉角度是(shi)(shi)(shi)(shi)否(fou)滿足精確的(de)(de)(de)(de)要(yao)求或是(shi)(shi)(shi)(shi)否(fou)會(hui)超出(chu)(chu)其(qi)(qi)量程）。但若(ruo)題(ti)(ti)目(mu)只(zhi)是(shi)(shi)(shi)(shi)說(shuo)此(ci)(ci)電(dian)(dian)(dian)(dian)(dian)表(biao)(biao)(biao)的(de)(de)(de)(de)內(nei)(nei)阻(zu)(zu)(zu)(zu)約(yue)為(wei)多少，則不(bu)能反(fan)串(chuan)。題(ti)(ti)目(mu)給(gei)出(chu)(chu)這(zhe)個(ge)條(tiao)件(jian)通常是(shi)(shi)(shi)(shi)用(yong)來考慮(lv)(lv)用(yong)外接法(fa)(fa)還(huan)是(shi)(shi)(shi)(shi)內(nei)(nei)接法(fa)(fa)的(de)(de)(de)(de)，此(ci)(ci)時應(ying)(ying)另尋(xun)他(ta)法(fa)(fa)。若(ruo)考慮(lv)(lv)用(yong)閉合電(dian)(dian)(dian)(dian)(dian)路(lu)歐姆定(ding)(ding)律測(ce)(ce)電(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)時，則應(ying)(ying)注意(yi)(yi)電(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)的(de)(de)(de)(de)兩(liang)(liang)個(ge)指(zhi)標即電(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)的(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)動勢(shi)E和內(nei)(nei)阻(zu)(zu)(zu)(zu)r。如果電(dian)(dian)(dian)(dian)(dian)動勢(shi)E和內(nei)(nei)阻(zu)(zu)(zu)(zu)r未知(zhi)，則應(ying)(ying)做待(dai)測(ce)(ce)量加(jia)以(yi)考慮(lv)(lv)。

三、體會例題，學會應變

例(li)1：2004年(nian)高考理綜（全(quan)國(guo)卷二）22題：用以下(xia)器材測(ce)量(liang)一待(dai)測(ce)電阻Rx的阻值（900～1000Ω）：電源E，具有一定內阻，電動勢(shi)約為9.0V；電壓表V1，量(liang)程為1.5V，內阻r1=750Ω；電壓表V2，量(liang)程為5V，內阻r2=2500Ω；滑線(xian)變阻器R，最(zui)大阻值約為100Ω；單刀單擲(zhi)開關K，導(dao)線(xian)若干(gan)。

(1) 測量(liang)(liang)中要(yao)求電壓表的(de)讀(du)數不小于其(qi)量(liang)(liang)程的(de)1/3，試畫出測量(liang)(liang)電阻Rx的(de)一種(zhong)實驗電路原(yuan)理圖(tu)（原(yuan)理圖(tu)中的(de)元件要(yao)用(yong)題圖(tu)中相應(ying)的(de)英文字母(mu)標注。

(2) 根據你所畫(hua)的電路原理(li)圖在題給的實物(wu)圖上畫(hua)出連線。

(3) 若(ruo)電壓表(biao)V1的讀數用(yong)U1表(biao)示(shi)，電壓表(biao)V2的讀數用(yong)U2表(biao)示(shi)，則由已知量和測得量表(biao)示(shi)Rx的公式(shi)為(wei)Rx=__________。

分析：首先(xian)考慮實(shi)驗原理(li)。若利(li)用(yong)伏安法(fa)測(ce)電(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)，則(ze)需測(ce)出(chu)Rx兩端的(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)和通(tong)(tong)(tong)過的(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)。雖然(ran)器材中沒有(you)電(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)表(biao)，但給(gei)出(chu)的(de)(de)(de)兩只(zhi)電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)表(biao)，既(ji)知道它(ta)們(men)的(de)(de)(de)量(liang)程，又知道它(ta)們(men)的(de)(de)(de)內阻(zu)，因此(ci)，當(dang)接在電(dian)(dian)(dian)(dian)(dian)(dian)路(lu)(lu)中時(shi)(shi)，既(ji)可(ke)(ke)(ke)直接讀(du)出(chu)它(ta)們(men)的(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)值(zhi)，又可(ke)(ke)(ke)算(suan)(suan)出(chu)通(tong)(tong)(tong)過它(ta)們(men)的(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)。由此(ci)可(ke)(ke)(ke)知，當(dang)用(yong)伏安法(fa)測(ce)電(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)Rx的(de)(de)(de)值(zhi)時(shi)(shi)可(ke)(ke)(ke)有(you)圖1或(huo)圖2所示(shi)的(de)(de)(de)兩種(zhong)電(dian)(dian)(dian)(dian)(dian)(dian)路(lu)(lu)。當(dang)用(yong)圖1所示(shi)電(dian)(dian)(dian)(dian)(dian)(dian)路(lu)(lu)時(shi)(shi)，Rx先(xian)與電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)表(biao)串聯(lian)(lian)，讀(du)出(chu)電(dian)(dian)(dian)(dian)(dian)(dian)表(biao)電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)從而算(suan)(suan)出(chu)通(tong)(tong)(tong)過電(dian)(dian)(dian)(dian)(dian)(dian)表(biao)的(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)也就(jiu)是(shi)通(tong)(tong)(tong)過Rx的(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)，然(ran)后再與另一只(zhi)電(dian)(dian)(dian)(dian)(dian)(dian)表(biao)V并聯(lian)(lian)直接讀(du)出(chu)電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)，此(ci)電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)減去(qu)的(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)即是(shi)Rx兩端的(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)，這樣(yang)就(jiu)可(ke)(ke)(ke)用(yong)歐(ou)姆定律算(suan)(suan)出(chu)Rx的(de)(de)(de)值(zhi)；當(dang)用(yong)圖2所示(shi)電(dian)(dian)(dian)(dian)(dian)(dian)路(lu)(lu)時(shi)(shi)，Rx先(xian)與電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)表(biao)V并聯(lian)(lian)，可(ke)(ke)(ke)直接讀(du)出(chu)Rx兩端的(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)，再與另一只(zhi)表(biao)串聯(lian)(lian)，由兩只(zhi)電(dian)(dian)(dian)(dian)(dian)(dian)表(biao)電(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)之差算(suan)(suan)出(chu)Rx中的(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)，同樣(yang)可(ke)(ke)(ke)用(yong)歐(ou)姆定律算(suan)(suan)出(chu)Rx的(de)(de)(de)值(zhi)。

接下來需要考慮的(de)(de)(de)是，對于(yu)上述每(mei)種電(dian)(dian)路，由于(yu)有(you)(you)兩(liang)只不同(tong)規格的(de)(de)(de)電(dian)(dian)壓(ya)表，則若在(zai)上述電(dian)(dian)路中將電(dian)(dian)壓(ya)表互換位置，就會有(you)(you)四種可能。但要注意(yi)題(ti)目(mu)有(you)(you)“電(dian)(dian)壓(ya)表的(de)(de)(de)讀數不小于(yu)其量程的(de)(de)(de)1/3”的(de)(de)(de)要求(qiu)，因此，每(mei)只電(dian)(dian)壓(ya)表接在(zai)何處應(ying)結合(he)它們的(de)(de)(de)量程和內(nei)阻(zu)做進一步(bu)的(de)(de)(de)分析。采用圖1電(dian)(dian)路時，

若為電(dian)(dian)(dian)壓(ya)(ya)表(biao)(biao)V1，V為電(dian)(dian)(dian)壓(ya)(ya)表(biao)(biao)V2，則(ze)當V1兩(liang)(liang)端的(de)(de)(de)(de)電(dian)(dian)(dian)壓(ya)(ya)達(da)到滿(man)偏時，可(ke)估(gu)算出(chu)并聯(lian)電(dian)(dian)(dian)路(lu)兩(liang)(liang)端的(de)(de)(de)(de)電(dian)(dian)(dian)壓(ya)(ya)即V2兩(liang)(liang)端的(de)(de)(de)(de)電(dian)(dian)(dian)壓(ya)(ya)可(ke)達(da)3V左(zuo)右，兩(liang)(liang)只(zhi)電(dian)(dian)(dian)壓(ya)(ya)表(biao)(biao)的(de)(de)(de)(de)讀(du)數(shu)均可(ke)超過其量程的(de)(de)(de)(de)1/3，滿(man)足題目(mu)要求；采用(yong)圖2電(dian)(dian)(dian)路(lu)時，可(ke)從兩(liang)(liang)只(zhi)電(dian)(dian)(dian)表(biao)(biao)通過的(de)(de)(de)(de)電(dian)(dian)(dian)流(liu)考慮(lv)，V測支路(lu)電(dian)(dian)(dian)流(liu)而測干路(lu)電(dian)(dian)(dian)流(liu)，量程應大些(xie)，故V用(yong)電(dian)(dian)(dian)壓(ya)(ya)表(biao)(biao)V1而用(yong)電(dian)(dian)(dian)壓(ya)(ya)表(biao)(biao)V2。

再次應考(kao)慮(lv)的(de)(de)是滑線變(bian)(bian)阻器(qi)的(de)(de)使(shi)用(yong)。由(you)于電(dian)源電(dian)動勢較大(da)，變(bian)(bian)阻器(qi)的(de)(de)最大(da)阻值比電(dian)壓(ya)表的(de)(de)內阻小(xiao)得多，故若把滑線變(bian)(bian)阻器(qi)串接在電(dian)路中即做限流使(shi)用(yong)，將會使(shi)電(dian)壓(ya)表超(chao)過(guo)量(liang)程(cheng)且操(cao)作不方便，因此應接成分壓(ya)電(dian)路。

需要(yao)說明的是(shi)，上述電路(lu)不必考慮內(nei)、外接的問題。因(yin)(yin)為Rx是(shi)算出來(lai)的，沒有因(yin)(yin)電壓(ya)表(biao)分(fen)(fen)流或電流表(biao)分(fen)(fen)壓(ya)帶來(lai)的系統誤差。

以上從(cong)原(yuan)理(li)出發討論了電阻測量(liang)設計性實驗的主要(yao)方(fang)法(fa)。電阻測量(liang)設計性實驗還有一些特殊方(fang)法(fa)如替代法(fa)等等，由于篇幅原(yuan)因，在此不再(zai)贅(zhui)述。

四、小(xiao)試牛(niu)刀，專題(ti)訓練(lian)

⑴用以下(xia)器(qi)材測(ce)量一待測(ce)電(dian)阻(zu)(zu)(zu)(zu)Rx的(de)阻(zu)(zu)(zu)(zu)值(zhi)(zhi)（約100Ω）：電(dian)源E，電(dian)動勢約為6.0V，內阻(zu)(zu)(zu)(zu)可忽略不計(ji)；電(dian)流表A1，量程為0~50mA，內電(dian)阻(zu)(zu)(zu)(zu)r1=20Ω；電(dian)流表A2，量程為0~300mA，內阻(zu)(zu)(zu)(zu)r2=4Ω；定值(zhi)(zhi)電(dian)阻(zu)(zu)(zu)(zu)R0，阻(zu)(zu)(zu)(zu)值(zhi)(zhi)R0=20Ω，滑動變阻(zu)(zu)(zu)(zu)器(qi)R，最大阻(zu)(zu)(zu)(zu)值(zhi)(zhi)為10Ω；單刀單擲開關S，導(dao)線若干(gan)。

①測量中要求兩塊電流表(biao)的讀數都不小于其量程的1/3，試畫出較準(zhun)確地測量電阻Rx的一種實驗電路原理圖（原理圖中的元件(jian)要用題(ti)圖中相應的英文字母標注(zhu)）。

②若(ruo)某(mou)次(ci)測(ce)量(liang)(liang)中(zhong)電流表A1的(de)示數為I1，電流表A2的(de)示數為I2．則由已知量(liang)(liang)和測(ce)量(liang)(liang)量(liang)(liang)計算Rx的(de)表達式為Rx=。（用相應英(ying)文字母表示）

⑵如果測(ce)(ce)量(liang)一(yi)個待(dai)測(ce)(ce)電(dian)(dian)(dian)(dian)阻(zu)(zu)R的(de)阻(zu)(zu)值(zhi)(zhi)(zhi)時，器(qi)材中(zhong)沒有給電(dian)(dian)(dian)(dian)壓表(biao)，給出(chu)的(de)器(qi)材是：電(dian)(dian)(dian)(dian)池(chi)(chi)（電(dian)(dian)(dian)(dian)動勢的(de)具體值(zhi)(zhi)(zhi)未知(zhi)，但(dan)內阻(zu)(zu)可忽(hu)略(lve)不(bu)計(ji)）、電(dian)(dian)(dian)(dian)流(liu)表(biao)（內阻(zu)(zu)可忽(hu)略(lve)不(bu)計(ji)）、滑動變阻(zu)(zu)器(qi)、定(ding)值(zhi)(zhi)(zhi)電(dian)(dian)(dian)(dian)阻(zu)(zu)R0（R0的(de)值(zhi)(zhi)(zhi)與用多用電(dian)(dian)(dian)(dian)表(biao)粗測(ce)(ce)出(chu)的(de)待(dai)測(ce)(ce)電(dian)(dian)(dian)(dian)阻(zu)(zu)R的(de)阻(zu)(zu)值(zhi)(zhi)(zhi)相(xiang)等(deng)），調節范(fan)圍在0.1Ω―9999.9Ω的(de)電(dian)(dian)(dian)(dian)阻(zu)(zu)箱R′（電(dian)(dian)(dian)(dian)阻(zu)(zu)箱的(de)最大值(zhi)(zhi)(zhi)大于待(dai)測(ce)(ce)電(dian)(dian)(dian)(dian)阻(zu)(zu)R的(de)阻(zu)(zu)值(zhi)(zhi)(zhi)）、單(dan)刀單(dan)擲開關(guan)、單(dan)刀雙擲開關(guan)、若干導線。測(ce)(ce)量(liang)前將待(dai)測(ce)(ce)電(dian)(dian)(dian)(dian)阻(zu)(zu)R和(he)(he)電(dian)(dian)(dian)(dian)流(liu)表(biao)串聯(lian)后直(zhi)接和(he)(he)電(dian)(dian)(dian)(dian)池(chi)(chi)相(xiang)連，電(dian)(dian)(dian)(dian)流(liu)表(biao)的(de)示數接近滿量(liang)程。

要(yao)求：①選用所給的(de)器材，設計兩個不(bu)同的(de)測量待(dai)測電阻R的(de)阻值的(de)電路，畫(hua)出電路圖(tu)；②簡要(yao)說(shuo)明實驗步(bu)驟，寫出最(zui)后的(de)測量結果（如果需要(yao)計算，則(ze)必須(xu)寫出計算公式）。

參考解答：

⑴解法Ⅰ：通過(guo)Rx的(de)(de)最大電(dian)(dian)流(liu)大于(yu)電(dian)(dian)流(liu)表(biao)(biao)A1的(de)(de)滿(man)偏電(dian)(dian)流(liu)且(qie)為電(dian)(dian)流(liu)表(biao)(biao)A2的(de)(de)滿(man)偏電(dian)(dian)流(liu)的(de)(de)1/5．測(ce)量中(zhong)要求兩塊電(dian)(dian)流(liu)表(biao)(biao)的(de)(de)讀數都(dou)不小于(yu)其量程的(de)(de)1/3，故(gu)可用電(dian)(dian)流(liu)表(biao)(biao)A1測(ce)Rx的(de)(de)電(dian)(dian)流(liu)；將(jiang)A2與R0串(chuan)聯后改(gai)裝為電(dian)(dian)壓(ya)表(biao)(biao)，此(ci)電(dian)(dian)壓(ya)表(biao)(biao)測(ce)出的(de)(de)是Rx與A1的(de)(de)端電(dian)(dian)壓(ya)，故(gu)。

解法Ⅱ：若(ruo)將電(dian)(dian)流表A1與Rx串聯(lian)后再與電(dian)(dian)流表A2并聯(lian)即用(yong)A2測(ce)其端電(dian)(dian)壓(ya)，則由(you)于當A2中的(de)電(dian)(dian)流較大時A1中的(de)電(dian)(dian)流將不(bu)會達到(dao)其量程的(de)1/3，故可(ke)用(yong)定值電(dian)(dian)阻R0來測(ce)電(dian)(dian)壓(ya)。

②（a）（替(ti)代法）撥(bo)動S使(shi)R接(jie)通(tong)，記(ji)錄電流表的(de)(de)示數(shu)(shu)；撥(bo)動S使(shi)R′接(jie)通(tong)，記(ji)錄電流表的(de)(de)示數(shu)(shu)與(yu)R接(jie)通(tong)時的(de)(de)示數(shu)(shu)相(xiang)同，記(ji)錄此(ci)時R′的(de)(de)值(zhi)R0′，則R＝R0′。

 （b）設電(dian)源(yuan)的電(dian)動勢為E，S閉合后通過電(dian)流表的示(shi)數為I1，S斷開時電(dian)流表的示(shi)數為I2，有E＝I1R，E＝I2（R＋R0），解得(de)。

（c）設(she)電(dian)源的(de)(de)電(dian)動勢(shi)為(wei)E，S閉合前將(jiang)R′調(diao)到最大值(zhi)（或較大值(zhi)），然(ran)后閉合S，調(diao)R′使(shi)電(dian)流(liu)(liu)表的(de)(de)示(shi)數盡量接近滿量程，此時R′的(de)(de)值(zhi)為(wei)R0′，電(dian)流(liu)(liu)表的(de)(de)示(shi)數為(wei)I1．斷開(kai)S后電(dian)流(liu)(liu)表的(de)(de)示(shi)數為(wei)I2（也可采(cai)用在S斷開(kai)后調(diao)節R′，使(shi)電(dian)流(liu)(liu)表的(de)(de)示(shi)數為(wei)1/2滿量程的(de)(de)方法(fa)）

參考文獻：

[1]教育(yu)部考(kao)試中心“高考(kao)內(nei)容、形(xing)式(shi)與能力(li)考(kao)查”課題組.物理－歷年高考(kao)試題精選解析(xi)[Z].北(bei)京：中國人民大學出版社，2004.

篇4

滑(hua)(hua)動變阻(zu)器(qi)是初中(zhong)電學中(zhong)實驗中(zhong)常用的(de)儀器(qi)，要求同學們(men)在(zai)理解滑(hua)(hua)動變阻(zu)器(qi)的(de)構造和原理的(de)基礎(chu)上，熟練掌握其使用方法以(yi)及滑(hua)(hua)動變阻(zu)器(qi)在(zai)電路中(zhong)所起的(de)作用.

一、滑動變阻器的(de)構(gou)造

滑(hua)(hua)(hua)動(dong)(dong)變(bian)阻器(qi)(qi)是一種(zhong)可(ke)以改變(bian)電(dian)阻大(da)小的(de)(de)儀器(qi)(qi)，實驗(yan)室里常用的(de)(de)滑(hua)(hua)(hua)動(dong)(dong)變(bian)阻器(qi)(qi)如(ru)圖(tu)2（a）所示.圖(tu)中的(de)(de)A、B、C、D為(wei)(wei)(wei)(wei)接(jie)線柱，①為(wei)(wei)(wei)(wei)表面涂(tu)(tu)有絕緣(yuan)(yuan)(yuan)漆的(de)(de)電(dian)阻絲；②為(wei)(wei)(wei)(wei)瓷(ci)管(guan)；③為(wei)(wei)(wei)(wei)金(jin)(jin)屬滑(hua)(hua)(hua)片(pian)P；④為(wei)(wei)(wei)(wei)金(jin)(jin)屬桿(gan)；⑤為(wei)(wei)(wei)(wei)支架(jia).滑(hua)(hua)(hua)動(dong)(dong)變(bian)阻器(qi)(qi)由瓷(ci)筒(tong)、線圈、金(jin)(jin)屬桿(gan)、滑(hua)(hua)(hua)片(pian)等元件構成.套在瓷(ci)筒(tong)上(shang)的(de)(de)線圈由表面涂(tu)(tu)有絕緣(yuan)(yuan)(yuan)漆的(de)(de)電(dian)阻絲（電(dian)阻率較大(da)的(de)(de)合金(jin)(jin)線）繞(rao)成，它的(de)(de)一個頭(tou)與接(jie)線柱A相(xiang)連，另一個頭(tou)與接(jie)線柱B相(xiang)連.瓷(ci)筒(tong)上(shang)方的(de)(de)金(jin)(jin)屬桿(gan)架(jia)在絕緣(yuan)(yuan)(yuan)瓷(ci)架(jia)上(shang)，桿(gan)的(de)(de)兩端有接(jie)線柱C和D，套在金(jin)(jin)屬桿(gan)上(shang)的(de)(de)金(jin)(jin)屬滑(hua)(hua)(hua)片(pian)可(ke)在棒上(shang)滑(hua)(hua)(hua)動(dong)(dong)，并與線圈緊密(mi)接(jie)觸(chu)，線圈上(shang)能接(jie)觸(chu)滑(hua)(hua)(hua)片(pian)的(de)(de)地方，絕緣(yuan)(yuan)(yuan)漆已被(bei)刮去.滑(hua)(hua)(hua)動(dong)(dong)變(bian)阻器(qi)(qi)銘牌上(shang)標有“20Ω 1A”的(de)(de)字樣，表示其可(ke)接(jie)入電(dian)路的(de)(de)最大(da)電(dian)阻是20Ω，允許(xu)通過(guo)此滑(hua)(hua)(hua)動(dong)(dong)變(bian)阻器(qi)(qi)的(de)(de)最大(da)電(dian)流是1A（否(fou)則會燒壞(huai)變(bian)阻器(qi)(qi)）.圖(tu)2（b）為(wei)(wei)(wei)(wei)滑(hua)(hua)(hua)動(dong)(dong)變(bian)阻器(qi)(qi)結構示意圖(tu)，圖(tu)2（c）為(wei)(wei)(wei)(wei)電(dian)路圖(tu)符號.

例(li)1 下表列出了4種長1m、橫截面積為(wei)1mm2的導線(xian)在(zai)20℃時的電阻值.由表中數據可知，架(jia)設輸電線(xian)，應(ying)選擇(ze) 導線(xian)；繞制滑(hua)動(dong)變阻器(qi)，應(ying)選用 導線(xian).

解析 實際生活(huo)中架設輸(shu)電(dian)線(xian)時，為了減少(shao)輸(shu)電(dian)線(xian)上電(dian)能(neng)的損耗，一般選擇電(dian)阻(zu)(zu)率(lv)小的材(cai)料做導線(xian)，也就是在導體長度、橫截面積和溫度相同(tong)時，電(dian)阻(zu)(zu)越小的材(cai)料；而(er)繞(rao)制滑動變阻(zu)(zu)器的線(xian)圈一般選用電(dian)阻(zu)(zu)率(lv)較大的材(cai)料.

答案 銅 鎳鉻(ge)合(he)金

二、滑(hua)動(dong)變阻器(qi)的原理及連接方式(shi)

導(dao)體(ti)(ti)的(de)電(dian)阻由導(dao)體(ti)(ti)的(de)長(chang)(chang)度(du)(du)(du)、橫(heng)截面積(ji)、材(cai)料(liao)和(he)溫度(du)(du)(du)等決定，即在溫度(du)(du)(du)一(yi)定時，如(ru)(ru)果導(dao)體(ti)(ti)的(de)長(chang)(chang)度(du)(du)(du)、橫(heng)截面積(ji)和(he)材(cai)料(liao)都(dou)確定了(le)，那么(me)導(dao)體(ti)(ti)的(de)電(dian)阻也就確定了(le).如(ru)(ru)何才能方便(bian)地(di)改變導(dao)體(ti)(ti)的(de)電(dian)阻呢(ni)？顯然(ran)我們(men)得想辦法改變影響(xiang)電(dian)阻大小的(de)其中一(yi)個因(yin)素或者(zhe)一(yi)些因(yin)素，通(tong)過大量(liang)實(shi)踐，我們(men)發(fa)現在材(cai)料(liao)、橫(heng)截面積(ji)、長(chang)(chang)度(du)(du)(du)及溫度(du)(du)(du)諸因(yin)素中，改變導(dao)體(ti)(ti)的(de)長(chang)(chang)度(du)(du)(du)最方便(bian).滑動變阻器正是通(tong)過改變電(dian)阻線的(de)長(chang)(chang)度(du)(du)(du)來改變電(dian)阻的(de).

例2 如(ru)圖3所示電路，導線(xian)a的(de)一(yi)端固定連接在鉛(qian)筆芯上，當導線(xian)b的(de)一(yi)端在鉛(qian)筆芯上左(zuo)右(you)移(yi)動時，燈(deng)泡亮(liang)暗會發生變化.這個實驗說(shuo)明(ming)鉛(qian)筆芯是 （選填(tian)“導體”或(huo)“絕(jue)緣體”），還能說(shuo)明(ming)導體的(de)電阻與 有關.受此啟發，人們(men)制造了(le)一(yi)種可以(yi)改變電阻的(de)元件，叫做 .

解析(xi) 根據(ju)鉛(qian)筆芯容易導電我們可(ke)以知(zhi)道它是(shi)導體，來回移動改變的是(shi)接入電路部分的鉛(qian)筆芯的長度.

答(da)案 導體 導體長度 滑動變(bian)阻器

我們知道了滑(hua)動變(bian)(bian)(bian)阻(zu)器(qi)的(de)(de)原理(li)之后，在使(shi)用滑(hua)動變(bian)(bian)(bian)阻(zu)器(qi)的(de)(de)時候就(jiu)一(yi)(yi)定要(yao)注(zhu)意到必須能(neng)改(gai)變(bian)(bian)(bian)接(jie)(jie)(jie)(jie)(jie)(jie)入(ru)(ru)電(dian)(dian)(dian)路(lu)(lu)中電(dian)(dian)(dian)阻(zu)絲(si)的(de)(de)長度，否則(ze)就(jiu)起(qi)不(bu)(bu)到改(gai)變(bian)(bian)(bian)電(dian)(dian)(dian)阻(zu)的(de)(de)目的(de)(de).對照(zhao)圖2（b），滑(hua)動變(bian)(bian)(bian)阻(zu)器(qi)的(de)(de)結構(gou)示意圖，我們一(yi)(yi)共有(you)這樣(yang)6種(zhong)連接(jie)(jie)(jie)(jie)(jie)(jie)方法(fa)：連接(jie)(jie)(jie)(jie)(jie)(jie)接(jie)(jie)(jie)(jie)(jie)(jie)線(xian)(xian)(xian)(xian)柱A和(he)B、A和(he)C、A和(he)D、B和(he)C、B和(he)D、C和(he)D.將接(jie)(jie)(jie)(jie)(jie)(jie)線(xian)(xian)(xian)(xian)柱A、C（或(huo)A、D）接(jie)(jie)(jie)(jie)(jie)(jie)入(ru)(ru)電(dian)(dian)(dian)路(lu)(lu)，接(jie)(jie)(jie)(jie)(jie)(jie)入(ru)(ru)電(dian)(dian)(dian)路(lu)(lu)的(de)(de)電(dian)(dian)(dian)阻(zu)線(xian)(xian)(xian)(xian)是(shi)AP段(duan)，若(ruo)滑(hua)片P向(xiang)(xiang)左移(yi)動，接(jie)(jie)(jie)(jie)(jie)(jie)入(ru)(ru)電(dian)(dian)(dian)路(lu)(lu)的(de)(de)電(dian)(dian)(dian)阻(zu)線(xian)(xian)(xian)(xian)變(bian)(bian)(bian)短(duan)，電(dian)(dian)(dian)阻(zu)變(bian)(bian)(bian)小(xiao)；反(fan)之，電(dian)(dian)(dian)阻(zu)變(bian)(bian)(bian)大.將接(jie)(jie)(jie)(jie)(jie)(jie)線(xian)(xian)(xian)(xian)柱B、D（或(huo)B、C）接(jie)(jie)(jie)(jie)(jie)(jie)入(ru)(ru)電(dian)(dian)(dian)路(lu)(lu)，接(jie)(jie)(jie)(jie)(jie)(jie)入(ru)(ru)電(dian)(dian)(dian)路(lu)(lu)的(de)(de)電(dian)(dian)(dian)阻(zu)線(xian)(xian)(xian)(xian)是(shi)BP段(duan)，若(ruo)滑(hua)片P向(xiang)(xiang)左移(yi)動，接(jie)(jie)(jie)(jie)(jie)(jie)入(ru)(ru)電(dian)(dian)(dian)路(lu)(lu)的(de)(de)電(dian)(dian)(dian)阻(zu)線(xian)(xian)(xian)(xian)變(bian)(bian)(bian)長，電(dian)(dian)(dian)阻(zu)變(bian)(bian)(bian)大；反(fan)之，電(dian)(dian)(dian)阻(zu)變(bian)(bian)(bian)小(xiao).將接(jie)(jie)(jie)(jie)(jie)(jie)線(xian)(xian)(xian)(xian)柱A、B接(jie)(jie)(jie)(jie)(jie)(jie)入(ru)(ru)電(dian)(dian)(dian)路(lu)(lu)，接(jie)(jie)(jie)(jie)(jie)(jie)入(ru)(ru)電(dian)(dian)(dian)路(lu)(lu)的(de)(de)電(dian)(dian)(dian)阻(zu)線(xian)(xian)(xian)(xian)是(shi)AB，無(wu)論滑(hua)片P向(xiang)(xiang)左還是(shi)向(xiang)(xiang)右移(yi)動，接(jie)(jie)(jie)(jie)(jie)(jie)入(ru)(ru)電(dian)(dian)(dian)路(lu)(lu)的(de)(de)電(dian)(dian)(dian)阻(zu)線(xian)(xian)(xian)(xian)長度不(bu)(bu)變(bian)(bian)(bian)，電(dian)(dian)(dian)阻(zu)不(bu)(bu)變(bian)(bian)(bian)，相(xiang)(xiang)當于接(jie)(jie)(jie)(jie)(jie)(jie)了一(yi)(yi)只定值電(dian)(dian)(dian)阻(zu).將接(jie)(jie)(jie)(jie)(jie)(jie)線(xian)(xian)(xian)(xian)柱C、D接(jie)(jie)(jie)(jie)(jie)(jie)入(ru)(ru)電(dian)(dian)(dian)路(lu)(lu)，電(dian)(dian)(dian)阻(zu)線(xian)(xian)(xian)(xian)沒有(you)接(jie)(jie)(jie)(jie)(jie)(jie)入(ru)(ru)電(dian)(dian)(dian)路(lu)(lu)，無(wu)論滑(hua)片P向(xiang)(xiang)左還是(shi)向(xiang)(xiang)右移(yi)動，C、D間電(dian)(dian)(dian)阻(zu)始終為零，相(xiang)(xiang)當于接(jie)(jie)(jie)(jie)(jie)(jie)了一(yi)(yi)根導線(xian)(xian)(xian)(xian).

通過上述分(fen)析，我們總結出滑動變阻器的使用方式(shi)及注意點：

（1）滑(hua)動變阻(zu)器的4個接線(xian)柱(zhu)正確接法是將上面和(he)下面各一(yi)(yi)個接線(xian)柱(zhu)接入電路，即(ji)總(zong)結為“一(yi)(yi)上一(yi)(yi)下”；

（2）為了保護(hu)電路，在電路開關閉合前，應把滑(hua)動變阻(zu)器的(de)滑(hua)片(pian)移到滑(hua)動變阻(zu)器接入電路的(de)阻(zu)值最大(da)的(de)位置，即(ji)下(xia)面用的(de)左邊(bian)接線柱(zhu)，那滑(hua)片(pian)就(jiu)放(fang)右端，反之亦然；

（3）通過滑(hua)動變(bian)阻器的電流不能超過其(qi)允許通過的最大電流值.

例(li)3 在(zai)如圖4所示的電路中，用(yong)滑(hua)動變阻器調節(jie)燈的亮度，若要求滑(hua)片P向(xiang)右(you)端(duan)滑(hua)動時燈逐漸變暗，則下列接法(fa)正確的是（ ）.

A.M接C，N接B

B.M接A，N接B

C.M接(jie)C，N接(jie)D

D.M接(jie)A，N接(jie)D

解析 根據滑(hua)(hua)動(dong)變(bian)阻器的(de)連接時(shi)需(xu)滿(man)足“一(yi)上一(yi)下(xia)”，排(pai)除B、C選項(xiang).由題意可知，滑(hua)(hua)片P向(xiang)(xiang)右端滑(hua)(hua)動(dong)時(shi)燈逐漸變(bian)暗，即電(dian)流變(bian)小，故要求(qiu)接入電(dian)路電(dian)阻變(bian)大(da)，P向(xiang)(xiang)右滑(hua)(hua)動(dong)時(shi)圖中(zhong)CP段(duan)變(bian)長，從而(er)很容易就能找到正(zheng)確答案.

答案 A

三、滑動(dong)變阻器的(de)作用

滑動變(bian)阻器在電路中所(suo)起的作用，一般(ban)有如(ru)下幾(ji)個(ge)方面(mian)：

（1）達(da)到(dao)保護(hu)電(dian)(dian)(dian)(dian)(dian)路(lu)(lu)安(an)(an)全的(de)(de)目(mu)的(de)(de).電(dian)(dian)(dian)(dian)(dian)路(lu)(lu)中(zhong)(zhong)電(dian)(dian)(dian)(dian)(dian)流(liu)過(guo)大(da)會容易引起一(yi)些器(qi)件(jian)的(de)(de)不安(an)(an)全使(shi)用(yong)(yong).根據歐(ou)姆定(ding)律I=■，當電(dian)(dian)(dian)(dian)(dian)源電(dian)(dian)(dian)(dian)(dian)壓一(yi)定(ding)時，電(dian)(dian)(dian)(dian)(dian)路(lu)(lu)的(de)(de)總(zong)電(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)越(yue)小，電(dian)(dian)(dian)(dian)(dian)流(liu)就越(yue)大(da)，電(dian)(dian)(dian)(dian)(dian)路(lu)(lu)中(zhong)(zhong)的(de)(de)某(mou)些元(yuan)件(jian)如電(dian)(dian)(dian)(dian)(dian)流(liu)表、燈(deng)泡(pao)等(deng)就越(yue)有(you)損壞(huai)的(de)(de)可能(neng).因(yin)此(ci)，在(zai)(zai)初中(zhong)(zhong)電(dian)(dian)(dian)(dian)(dian)學實(shi)驗(yan)(yan)涉及電(dian)(dian)(dian)(dian)(dian)流(liu)表等(deng)的(de)(de)多個(ge)電(dian)(dian)(dian)(dian)(dian)學實(shi)驗(yan)(yan)中(zhong)(zhong)，都配(pei)有(you)滑動變阻(zu)(zu)器(qi).實(shi)驗(yan)(yan)一(yi)再強(qiang)調和要(yao)求(qiu)，連接電(dian)(dian)(dian)(dian)(dian)路(lu)(lu)前開(kai)關(guan)必(bi)須斷開(kai)，電(dian)(dian)(dian)(dian)(dian)路(lu)(lu)連接完畢閉(bi)合開(kai)關(guan)前，一(yi)定(ding)要(yao)將滑動變阻(zu)(zu)器(qi)在(zai)(zai)電(dian)(dian)(dian)(dian)(dian)路(lu)(lu)中(zhong)(zhong)的(de)(de)阻(zu)(zu)值調至最(zui)大(da).目(mu)的(de)(de)是為了盡(jin)可能(neng)增大(da)電(dian)(dian)(dian)(dian)(dian)路(lu)(lu)的(de)(de)總(zong)電(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)，使(shi)電(dian)(dian)(dian)(dian)(dian)路(lu)(lu)中(zhong)(zhong)的(de)(de)電(dian)(dian)(dian)(dian)(dian)流(liu)達(da)到(dao)最(zui)小，從而達(da)到(dao)保護(hu)電(dian)(dian)(dian)(dian)(dian)路(lu)(lu)的(de)(de)目(mu)的(de)(de).如伏(fu)安(an)(an)法測電(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)、用(yong)(yong)電(dian)(dian)(dian)(dian)(dian)流(liu)表和電(dian)(dian)(dian)(dian)(dian)壓表測小燈(deng)泡(pao)的(de)(de)電(dian)(dian)(dian)(dian)(dian)功率等(deng)實(shi)驗(yan)(yan)都利(li)用(yong)(yong)了滑動變阻(zu)(zu)器(qi)保護(hu)電(dian)(dian)(dian)(dian)(dian)路(lu)(lu)的(de)(de)作用(yong)(yong).

例4 九年(nian)級某班同學做“用滑動變(bian)(bian)阻(zu)器改變(bian)(bian)電流”的實驗，電路如圖5所示.

①連(lian)接(jie)實物時(shi)，開(kai)關(guan)應(ying)當 ，為了保護電路安全，滑片P應(ying)移動(dong)最(zui)

端（選填“左(zuo)”或“右”）；

②開(kai)始實驗后，甲同學發(fa)現無論怎樣(yang)移動(dong)(dong)滑片(pian)P，燈(deng)的亮(liang)度都(dou)不發(fa)生變化，而且一直很(hen)暗，這可(ke)(ke)能(neng)是(shi)(shi) ；乙同學發(fa)現無論怎樣(yang)移動(dong)(dong)滑片(pian)P，燈(deng)一直很(hen)亮(liang)，這可(ke)(ke)能(neng)是(shi)(shi) ；丙(bing)同學緩慢移動(dong)(dong)滑片(pian)P時，看到燈(deng)忽(hu)然亮(liang)又(you)忽(hu)然不亮(liang)，這可(ke)(ke)能(neng)是(shi)(shi) .

解析 連接(jie)電(dian)(dian)(dian)(dian)路(lu)時，為了(le)保護電(dian)(dian)(dian)(dian)路(lu)安全，開(kai)關(guan)必(bi)須斷開(kai)，連接(jie)完畢要檢查無誤后方可閉(bi)合開(kai)關(guan)，不過(guo)在閉(bi)合開(kai)關(guan)前還要注意(yi)使電(dian)(dian)(dian)(dian)路(lu)接(jie)入(ru)的電(dian)(dian)(dian)(dian)阻(zu)最(zui)大(da)(da)，也就是滑片(pian)(pian)必(bi)須放在阻(zu)值(zhi)最(zui)大(da)(da)端(duan)，即(ji)滑片(pian)(pian)P距離下面(mian)接(jie)入(ru)的接(jie)線(xian)柱距離最(zui)遠.如果滑動變(bian)阻(zu)器(qi)連接(jie)錯誤（同(tong)為上面(mian)或者同(tong)為下面(mian)兩接(jie)線(xian)柱）的話，那滑片(pian)(pian)移(yi)(yi)動就無法(fa)(fa)改變(bian)電(dian)(dian)(dian)(dian)阻(zu)，從而(er)無法(fa)(fa)改變(bian)電(dian)(dian)(dian)(dian)流(liu)，它們的區別(bie)就是同(tong)為下面(mian)兩接(jie)線(xian)柱，滑動變(bian)阻(zu)器(qi)全部電(dian)(dian)(dian)(dian)阻(zu)接(jie)入(ru)電(dian)(dian)(dian)(dian)路(lu)，電(dian)(dian)(dian)(dian)阻(zu)最(zui)大(da)(da)，電(dian)(dian)(dian)(dian)流(liu)最(zui)小，引起的現象是電(dian)(dian)(dian)(dian)流(liu)表示(shi)(shi)數偏(pian)小或者燈泡最(zui)暗，反之電(dian)(dian)(dian)(dian)流(liu)表示(shi)(shi)數偏(pian)大(da)(da)，燈泡很亮.題(ti)中緩慢移(yi)(yi)動滑片(pian)(pian)P時，看到(dao)燈忽(hu)亮忽(hu)不亮，說明滑片(pian)(pian)處接(jie)觸不好(hao).

答案 ①斷開 右 ②滑動(dong)變(bian)阻器連(lian)接(jie)的是(shi)下(xia)面兩(liang)個接(jie)線(xian)(xian)柱 滑動(dong)變(bian)阻器連(lian)接(jie)的是(shi)上面兩(liang)個接(jie)線(xian)(xian)柱 接(jie)觸不良

（2）改變電(dian)(dian)(dian)(dian)(dian)路(lu)(lu)中(zhong)的(de)(de)電(dian)(dian)(dian)(dian)(dian)流及(ji)改變導體兩端電(dian)(dian)(dian)(dian)(dian)壓(ya)，以(yi)達到(dao)調節燈泡亮度或者多(duo)次實(shi)驗(yan)的(de)(de)目(mu)的(de)(de).通過改變滑動變阻器接入電(dian)(dian)(dian)(dian)(dian)路(lu)(lu)電(dian)(dian)(dian)(dian)(dian)阻大(da)小，根據歐姆(mu)定律I=■，電(dian)(dian)(dian)(dian)(dian)壓(ya)一定時，電(dian)(dian)(dian)(dian)(dian)路(lu)(lu)總電(dian)(dian)(dian)(dian)(dian)阻越大(da)，總電(dian)(dian)(dian)(dian)(dian)流就(jiu)越小，從(cong)而(er)來改變電(dian)(dian)(dian)(dian)(dian)路(lu)(lu)電(dian)(dian)(dian)(dian)(dian)流；再由U=IR，電(dian)(dian)(dian)(dian)(dian)阻一定時，導體兩端電(dian)(dian)(dian)(dian)(dian)壓(ya)就(jiu)跟(gen)著改變，從(cong)而(er)改變導體兩端電(dian)(dian)(dian)(dian)(dian)壓(ya).當然，在實(shi)驗(yan)過程中(zhong)，多(duo)次改變了電(dian)(dian)(dian)(dian)(dian)流和(he)電(dian)(dian)(dian)(dian)(dian)壓(ya)，可以(yi)避(bi)免實(shi)驗(yan)結果偶然性或者實(shi)現多(duo)次實(shi)驗(yan)減小誤差的(de)(de)目(mu)的(de)(de).

下面是初(chu)中電學實驗滑動變阻(zu)器(qi)的作用(yong)列(lie)舉：

（1）探究歐姆(mu)定律中電(dian)(dian)流(liu)與電(dian)(dian)壓(ya)的關(guan)系——為了保(bao)證兩端的電(dian)(dian)壓(ya)不變(bian)；

（2）探究歐姆定律(lv)(lv)中電(dian)流(liu)與電(dian)阻(zu)的關系——改變(bian)定值電(dian)阻(zu)兩(liang)端電(dian)壓，從(cong)而達(da)到多(duo)次實驗探究規律(lv)(lv)的作用；

（3）測定小燈泡的電阻(zu)——改變小燈泡兩端電壓，達到(dao)多次測試取平均值以減(jian)小誤差的目的；

當然，這(zhe)里的滑動變阻(zu)器也同樣有改變電(dian)(dian)流(liu)、電(dian)(dian)壓、保護電(dian)(dian)路等作用.

例5 如圖(tu)6所示的電路(lu)中，電源電壓恒(heng)定(ding)，R1為(wei)定(ding)值電阻.閉合開關S，滑動變阻器R2的滑片(pian)P由b端移到a端的過程(cheng)中，下列說(shuo)法中正(zheng)確的是(shi)（ ）.

A.電壓表(biao)和電流(liu)表(biao)的示數都(dou)變(bian)大(da)

B.電壓表和(he)電流(liu)表的示數都變小

C.電壓表(biao)示數(shu)變大(da)，電流(liu)表(biao)示數(shu)變小

D.電(dian)(dian)壓表示(shi)數變小，電(dian)(dian)流表示(shi)數變大

解(jie)析(xi) 首先(xian)分(fen)析(xi)電(dian)(dian)(dian)(dian)路(lu)(lu)(lu)圖(tu)：定值(zhi)電(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)R1與滑(hua)(hua)動變(bian)(bian)阻(zu)(zu)(zu)(zu)器(qi)(qi)(qi)(qi)R2串聯(lian)，電(dian)(dian)(dian)(dian)流(liu)表(biao)測量(liang)(liang)的(de)(de)(de)(de)(de)是(shi)整個電(dian)(dian)(dian)(dian)路(lu)(lu)(lu)中(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)流(liu)，電(dian)(dian)(dian)(dian)壓(ya)表(biao)并聯(lian)在定值(zhi)電(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)兩端，測量(liang)(liang)的(de)(de)(de)(de)(de)是(shi)定值(zhi)電(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)兩端的(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)壓(ya)；當滑(hua)(hua)動變(bian)(bian)阻(zu)(zu)(zu)(zu)器(qi)(qi)(qi)(qi)的(de)(de)(de)(de)(de)滑(hua)(hua)片P由b端移(yi)到(dao)a端的(de)(de)(de)(de)(de)過程中(zhong)(zhong)(zhong)，分(fen)析(xi)滑(hua)(hua)動變(bian)(bian)阻(zu)(zu)(zu)(zu)器(qi)(qi)(qi)(qi)接入(ru)電(dian)(dian)(dian)(dian)路(lu)(lu)(lu)中(zhong)(zhong)(zhong)的(de)(de)(de)(de)(de)阻(zu)(zu)(zu)(zu)值(zhi)的(de)(de)(de)(de)(de)變(bian)(bian)化(hua)，再(zai)利(li)用串聯(lian)電(dian)(dian)(dian)(dian)路(lu)(lu)(lu)電(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)的(de)(de)(de)(de)(de)特點，判(pan)(pan)斷出(chu)電(dian)(dian)(dian)(dian)路(lu)(lu)(lu)中(zhong)(zhong)(zhong)總電(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)的(de)(de)(de)(de)(de)變(bian)(bian)化(hua)，結(jie)合歐(ou)姆定律(lv)I=■確定電(dian)(dian)(dian)(dian)流(liu)表(biao)示數(shu)的(de)(de)(de)(de)(de)變(bian)(bian)化(hua)情況；定值(zhi)電(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)R1的(de)(de)(de)(de)(de)阻(zu)(zu)(zu)(zu)值(zhi)不變(bian)(bian)，可(ke)利(li)用公式U=IR判(pan)(pan)斷出(chu)定值(zhi)電(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)R1兩端電(dian)(dian)(dian)(dian)壓(ya)的(de)(de)(de)(de)(de)變(bian)(bian)化(hua)情況，即電(dian)(dian)(dian)(dian)壓(ya)表(biao)示數(shu)的(de)(de)(de)(de)(de)變(bian)(bian)化(hua)情況.本(ben)題考(kao)查歐(ou)姆定律(lv)公式及其(qi)變(bian)(bian)形的(de)(de)(de)(de)(de)靈活運用，難點是(shi)判(pan)(pan)斷滑(hua)(hua)動變(bian)(bian)阻(zu)(zu)(zu)(zu)器(qi)(qi)(qi)(qi)滑(hua)(hua)片移(yi)動過程中(zhong)(zhong)(zhong)電(dian)(dian)(dian)(dian)路(lu)(lu)(lu)電(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)的(de)(de)(de)(de)(de)變(bian)(bian)化(hua)，要知(zhi)道串聯(lian)電(dian)(dian)(dian)(dian)路(lu)(lu)(lu)電(dian)(dian)(dian)(dian)流(liu)和電(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)的(de)(de)(de)(de)(de)規律(lv).

答案 A

（3）生活中的(de)(de)(de)變(bian)(bian)形變(bian)(bian)阻器及應用.利(li)用滑(hua)動變(bian)(bian)阻器改(gai)變(bian)(bian)接入電(dian)(dian)路電(dian)(dian)阻從而改(gai)變(bian)(bian)電(dian)(dian)流的(de)(de)(de)作用，在實際生活中有很多應用.比如改(gai)變(bian)(bian)電(dian)(dian)燈的(de)(de)(de)亮度、音響的(de)(de)(de)音量、貨車(che)實施計(ji)重收費、風力(li)測試、汽車(che)油量表(biao)等.

例6 如圖7是(shi)一(yi)個自(zi)動(dong)體重測試儀的(de)工作(zuo)原理圖，有(you)關它的(de)說法(fa)正確的(de)是(shi)（ ）.

A.體重顯示表是用電壓表改(gai)裝成的

B.體重測試儀電路(lu)由于缺少開(kai)關(guan)，始終處于通(tong)路(lu)

C.體(ti)重(zhong)(zhong)越大，體(ti)重(zhong)(zhong)顯示表(biao)的示數越大

D.體重(zhong)越小(xiao)，體重(zhong)顯示表的示數越大(da)

解析 圖中(zhong)的(de)R2就是一個變形的(de)滑(hua)動變阻(zu)(zu)(zu)器，R1為定(ding)值(zhi)電(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)，體重(zhong)顯示(shi)(shi)表串聯(lian)在(zai)電(dian)(dian)(dian)(dian)路中(zhong)，根(gen)據(ju)電(dian)(dian)(dian)(dian)流表和電(dian)(dian)(dian)(dian)壓表的(de)連接特(te)點，應(ying)該為電(dian)(dian)(dian)(dian)流表改裝(zhuang)；測試臺上未加(jia)重(zhong)力，此時滑(hua)片P處于(yu)A端絕(jue)緣處，電(dian)(dian)(dian)(dian)路處于(yu)斷開狀態；隨著(zhu)測試的(de)體重(zhong)越大(da)，滑(hua)片P向上移動，R2接入的(de)部分(fen)電(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)越來越小，電(dian)(dian)(dian)(dian)路總(zong)電(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)也就越小，電(dian)(dian)(dian)(dian)源電(dian)(dian)(dian)(dian)壓一定(ding)時，根(gen)據(ju)歐姆定(ding)律(lv)，電(dian)(dian)(dian)(dian)路電(dian)(dian)(dian)(dian)流就越來越大(da)，體重(zhong)顯示(shi)(shi)表示(shi)(shi)數也越大(da).

篇5

初中階段，學生的(de)(de)(de)抽(chou)象思維(wei)和邏輯思維(wei)能力(li)在不斷地形成與發展(zhan)，抽(chou)象的(de)(de)(de)概(gai)念(nian)和規律(lv)不易理(li)解和接受。在物理(li)教(jiao)學中，如何突(tu)破知識的(de)(de)(de)重(zhong)點和難(nan)點，幫助學生找(zhao)到知識的(de)(de)(de)竅(qiao)門(men)和解決問(wen)題的(de)(de)(de)突(tu)破口(kou)。“授之以漁(yu)”是物理(li)教(jiao)學中的(de)(de)(de)重(zhong)要課題。在教(jiao)學實踐中，筆者用(yong)以下方法來突(tu)破電學部分的(de)(de)(de)重(zhong)難(nan)點，效果(guo)極(ji)佳。

一、避輕就(jiu)重 巧抓重點

重點(dian)(dian)知(zhi)識(shi)與其它知(zhi)識(shi)有(you)著密(mi)不可(ke)分的(de)關系，很多知(zhi)識(shi)點(dian)(dian)往往由(you)重點(dian)(dian)知(zhi)識(shi)派生而來(lai)，教學中(zhong)(zhong)(zhong)應(ying)集中(zhong)(zhong)(zhong)主(zhu)要(yao)精力(li)，去(qu)講(jiang)深進透重點(dian)(dian)知(zhi)識(shi)，非(fei)重點(dian)(dian)知(zhi)識(shi)便迎(ying)刃而解了。若(ruo)不深入挖(wa)掘重點(dian)(dian)，胡子眉毛一把抓(zhua)，最終(zhong)只會導致“剪不斷，理還亂”的(de)結果。當然，忽視(shi)非(fei)重點(dian)(dian)也是(shi)有(you)失偏頗的(de)，教學中(zhong)(zhong)(zhong)應(ying)將重點(dian)(dian)、非(fei)重點(dian)(dian)知(zhi)識(shi)結合起來(lai)，在突出重點(dian)(dian)的(de)本文由(you)收集整理同時(shi)，使學生對所(suo)學知(zhi)識(shi)形成一個完整的(de)網絡，使思維得(de)到強化的(de)訓(xun)練，能力(li)得(de)到應(ying)有(you)的(de)提高。例如，在初中(zhong)(zhong)(zhong)階段(duan)，一般認為電(dian)(dian)(dian)流表(biao)(biao)的(de)電(dian)(dian)(dian)阻為零，電(dian)(dian)(dian)壓表(biao)(biao)的(de)電(dian)(dian)(dian)阻為無(wu)限(xian)大。把電(dian)(dian)(dian)流表(biao)(biao)當作導線，電(dian)(dian)(dian)壓表(biao)(biao)視(shi)為開路(lu)；用字母標出電(dian)(dian)(dian)路(lu)圖中(zhong)(zhong)(zhong)三條(tiao)導線相(xiang)交(jiao)的(de)結點(dian)(dian)；從電(dian)(dian)(dian)源的(de)正極出發，根據電(dian)(dian)(dian)流的(de)路(lu)徑及各個結點(dian)(dian)的(de)位(wei)置畫出簡單的(de)電(dian)(dian)(dian)路(lu)圖；電(dian)(dian)(dian)流表(biao)(biao)和電(dian)(dian)(dian)壓表(biao)(biao)復位(wei)。

例(li)1：請你畫出如圖1所示的(de)電路(lu)的(de)等效(xiao)電路(lu)圖，并說明電流表和電壓表的(de)作用。

圖1 圖2 圖3

解：（1）把(ba)電(dian)流(liu)表(biao)當作導線，電(dian)壓表(biao)視為(wei)開(kai)路。

（2）標(biao)出電路(lu)圖的結點a、b、c、d。

（3）根據(ju)電(dian)流路(lu)(lu)徑，電(dian)流由電(dian)源(yuan)正極出(chu)(chu)發經(jing)過(guo)d點(dian)(dian)和(he)r1來(lai)到a點(dian)(dian)，電(dian)流在(zai)a點(dian)(dian)分開兩路(lu)(lu)，一路(lu)(lu)通(tong)(tong)過(guo)r2到達(da)b點(dian)(dian)，另一路(lu)(lu)通(tong)(tong)過(guo)r3到達(da)b點(dian)(dian)，兩路(lu)(lu)在(zai)b點(dian)(dian)匯合到達(da)電(dian)源(yuan)負極形成回路(lu)(lu)。畫(hua)出(chu)(chu)簡單易看的電(dian)路(lu)(lu)圖（如(ru)圖2）。由此可知r2、r3是并聯，然后再與r1串聯。

（4）電(dian)(dian)(dian)(dian)流(liu)(liu)表(biao)(biao)(biao)電(dian)(dian)(dian)(dian)壓表(biao)(biao)(biao)復位。由電(dian)(dian)(dian)(dian)路(lu)圖1可知c、a兩(liang)(liang)點(dian)之間(jian)用導線(xian)連接(jie)在一(yi)(yi)起(qi)可看作同一(yi)(yi)點(dian)，電(dian)(dian)(dian)(dian)壓表(biao)(biao)(biao)的兩(liang)(liang)個接(jie)線(xian)柱分(fen)別連接(jie)d點(dian)和a點(dian)，所以(yi)電(dian)(dian)(dian)(dian)壓表(biao)(biao)(biao)是(shi)測量r1兩(liang)(liang)端的電(dian)(dian)(dian)(dian)壓。電(dian)(dian)(dian)(dian)流(liu)(liu)通(tong)過(guo)a點(dian)分(fen)開兩(liang)(liang)路(lu)，一(yi)(yi)路(lu)經過(guo)電(dian)(dian)(dian)(dian)流(liu)(liu)表(biao)(biao)(biao)后，再經過(guo)r3到達(da)b點(dian)，所以(yi)電(dian)(dian)(dian)(dian)流(liu)(liu)表(biao)(biao)(biao)是(shi)測量通(tong)過(guo)r3的電(dian)(dian)(dian)(dian)流(liu)(liu)強度（如(ru)圖3）。

由上面例子(zi)，可看出分析(xi)電(dian)路的(de)重要(yao)性。在復習(xi)中應特別(bie)強調分析(xi)電(dian)路，畫等(deng)效電(dian)路圖的(de)必要(yao)性，使學生(sheng)掌握這(zhe)個基本技能。并能養成遇(yu)到電(dian)學問(wen)題，先畫出電(dian)路圖。遇(yu)到電(dian)路圖先分析(xi)電(dian)路的(de)好習(xi)慣。

歐(ou)(ou)姆定律是初(chu)中(zhong)電學(xue)(xue)計(ji)算(suan)的核(he)心。它(ta)揭示了電學(xue)(xue)三個最重要的物理量：電流、電壓、電阻之(zhi)間(jian)的關(guan)系。在運用歐(ou)(ou)姆定律時，應特別注意：

①要明確定(ding)律(lv)中涉及(ji)的(de)u、i、r。是(shi)同(tong)一部分電(dian)路的(de)三個物理量(liang)。決(jue)不能張(zhang)冠(guan)李戴把不屬于同(tong)一電(dian)路中的(de)u、i、r代入公(gong)式中計算。

②公式(shi)i=u/r、u=ir 、r=u/i，單從數(shu)學意(yi)義上并無(wu)本質(zhi)不(bu)(bu)同，但從物理角度必須注意(yi)因(yin)果關(guan)系(xi)，電(dian)(dian)(dian)壓是形成(cheng)(cheng)電(dian)(dian)(dian)流(liu)的原(yuan)因(yin)，電(dian)(dian)(dian)阻是阻礙電(dian)(dian)(dian)流(liu)的內阻，不(bu)(bu)能錯(cuo)誤地認為“電(dian)(dian)(dian)阻跟電(dian)(dian)(dian)壓成(cheng)(cheng)正比(bi)，跟電(dian)(dian)(dian)流(liu)成(cheng)(cheng)反比(bi)”，也不(bu)(bu)能認為“導體兩端沒有電(dian)(dian)(dian)壓就沒有電(dian)(dian)(dian)阻”。

例2：如圖4所示，有兩個電(dian)(dian)阻(zu)r1、r2串聯，電(dian)(dian)源電(dian)(dian)壓為6伏，電(dian)(dian)阻(zu)r1的阻(zu)值(zhi)為10歐，電(dian)(dian)阻(zu)r2兩端的電(dian)(dian)壓為2伏。求：通(tong)過電(dian)(dian)阻(zu)r1的電(dian)(dian)流(liu)及(ji)電(dian)(dian)阻(zu)r2的電(dian)(dian)阻(zu)值(zhi)。

解：由串(chuan)聯電路的特點可(ke)知：

u1=u - u2 =6v -2v =4v，i1= = =0.4a，∴r2= = =5 ?

這(zhe)道例題是(shi)強調(diao)運用歐(ou)姆定律(lv)時，u、i、r的對(dui)應性。決不能(neng)用r2兩端的電壓(ya)或電源電壓(ya)除以r1的電阻值來求得通過 的電流，或用電源電壓(ya)除以電流來求得r2的電阻值。

二、精講善(shan)導 啟發智能

啟(qi)發(fa)(fa)教(jiao)(jiao)學是(shi)啟(qi)發(fa)(fa)學生(sheng)智能(neng)的(de)(de)教(jiao)(jiao)學。子曰：“不憤不啟(qi)”、“不悱不發(fa)(fa)”。葉圣(sheng)陶提出的(de)(de)“教(jiao)(jiao)是(shi)為了(le)達(da)到不需要教(jiao)(jiao)”的(de)(de)教(jiao)(jiao)育思(si)想(xiang)，都明確了(le)教(jiao)(jiao)學這(zhe)一認識活動(dong)是(shi)主觀見諸于(yu)(yu)客觀的(de)(de)過(guo)(guo)程，是(shi)學生(sheng)這(zhe)一教(jiao)(jiao)學的(de)(de)主體在教(jiao)(jiao)師的(de)(de)主導(dao)(dao)下，去接(jie)(jie)受教(jiao)(jiao)育的(de)(de)過(guo)(guo)程。事(shi)實(shi)說明，只有(you)把教(jiao)(jiao)學中(zhong)的(de)(de)主體思(si)維啟(qi)發(fa)(fa)起來，他們才能(neng)夠主動(dong)地吸收新(xin)的(de)(de)知識，接(jie)(jie)受新(xin)的(de)(de)思(si)想(xiang)，教(jiao)(jiao)學過(guo)(guo)程中(zhong)，強化(hua)對重點知識的(de)(de)啟(qi)發(fa)(fa)，有(you)利于(yu)(yu)啟(qi)發(fa)(fa)學生(sheng)的(de)(de)思(si)維，提高實(shi)踐能(neng)力。例如在教(jiao)(jiao)材(cai)中(zhong)，只給出了(le)“整(zheng)體短(duan)(duan)路(lu)”的(de)(de)概念，“導(dao)(dao)線不經過(guo)(guo)用電(dian)器(qi)直接(jie)(jie)跟電(dian)源兩極(ji)連接(jie)(jie)的(de)(de)電(dian)路(lu)，叫短(duan)(duan)路(lu)。”而在電(dian)學綜合(he)題中(zhong)常(chang)常(chang)會(hui)出現局(ju)部(bu)短(duan)(duan)路(lu)的(de)(de)問題，如果(guo)導(dao)(dao)線不經過(guo)(guo)其(qi)他用電(dian)器(qi)而將某個用電(dian)器(qi)（或某部(bu)分(fen)電(dian)路(lu)）首尾相連就(jiu)形(xing)成局(ju)部(bu)短(duan)(duan)路(lu)。局(ju)部(bu)短(duan)(duan)路(lu)僅造成用電(dian)器(qi)不工作，并不損壞用電(dian)器(qi)，因此是(shi)允許的(de)(de)。因它富于(yu)(yu)變化(hua)成為電(dian)學問題中(zhong)的(de)(de)一個難點。局(ju)部(bu)短(duan)(duan)

路概念抽(chou)象，學生難以理解(jie)。可用實驗(yan)幫助學生突破此難點(dian)。實驗(yan)原(yuan)理如圖(tu)5，當開關s閉合前，兩(liang)燈(deng)均亮（較(jiao)暗）；閉合后(hou)，l1不(bu)(bu)亮，而l2仍發光（較(jiao)亮）。為了(le)幫助初中生理解(jie)，可將l1比(bi)作是(shi)電流需通過的“一(yi)座高山(shan)(shan)”而開關s的短路通道則(ze)比(bi)作是(shi)“山(shan)(shan)里的一(yi)條隧洞(dong)”。有(you)了(le)“隧洞(dong)”，電流只(zhi)會(hui)“走隧洞(dong)”而不(bu)(bu)會(hui)去“爬山(shan)(shan)”。

三、綜合分析 總結方法(fa)

在(zai)(zai)進(jin)行(xing)(xing)知(zhi)(zhi)識系(xi)統化和(he)整體化的(de)(de)(de)(de)(de)教學(xue)(xue)(xue)中，教會學(xue)(xue)(xue)生分析、歸納問(wen)題(ti)(ti)，對他們進(jin)行(xing)(xing)解(jie)(jie)題(ti)(ti)方(fang)法(fa)指導(dao)，強化系(xi)列訓練是鞏固、理(li)(li)(li)解(jie)(jie)物理(li)(li)(li)概念提高實(shi)踐創新能(neng)(neng)力的(de)(de)(de)(de)(de)關鍵(jian)環(huan)節(jie)。有不少(shao)學(xue)(xue)(xue)生沉迷于(yu)題(ti)(ti)海之中，遇(yu)到困難頭皮發麻、束手(shou)無策(ce)。究其(qi)原因，除了概念不清、規律(lv)不明(ming)、能(neng)(neng)力薄弱之外，還有一(yi)個(ge)(ge)主要的(de)(de)(de)(de)(de)原因就是“只(zhi)埋(mai)頭拉車，不抬頭看路(lu)(lu)(lu)(lu)，”走馬觀花、囫圇(lun)吞棗(zao)、不抓(zhua)住(zhu)本質去透徹理(li)(li)(li)解(jie)(jie)，不善于(yu)歸納總(zong)(zong)結解(jie)(jie)題(ti)(ti)的(de)(de)(de)(de)(de)經驗方(fang)法(fa)。例如(ru)不少(shao)初中學(xue)(xue)(xue)生反映(ying)，電(dian)(dian)(dian)(dian)學(xue)(xue)(xue)習題(ti)(ti)涉及概念、公式多，解(jie)(jie)題(ti)(ti)頭緒多，容易(yi)出(chu)(chu)錯(cuo)。要突破(po)這個(ge)(ge)難點(dian)，關鍵(jian)在(zai)(zai)于(yu)整理(li)(li)(li)出(chu)(chu)清晰的(de)(de)(de)(de)(de)解(jie)(jie)題(ti)(ti)思(si)路(lu)(lu)(lu)(lu)。在(zai)(zai)這里(li)可(ke)(ke)以使用(yong)“表(biao)(biao)格法(fa)”幫助(zhu)學(xue)(xue)(xue)生整理(li)(li)(li)解(jie)(jie)題(ti)(ti)思(si)路(lu)(lu)(lu)(lu)。表(biao)(biao)格的(de)(de)(de)(de)(de)列，列出(chu)(chu)有關用(yong)電(dian)(dian)(dian)(dian)器(qi)的(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)流、電(dian)(dian)(dian)(dian)壓(ya)、電(dian)(dian)(dian)(dian)阻(zu)、電(dian)(dian)(dian)(dian)功率(lv)(lv)四(si)個(ge)(ge)物理(li)(li)(li)量。在(zai)(zai)一(yi)般計算(suan)中，出(chu)(chu)現用(yong)電(dian)(dian)(dian)(dian)器(qi)多為純電(dian)(dian)(dian)(dian)阻(zu)，根據歐姆定(ding)律(lv)i=u/r，電(dian)(dian)(dian)(dian)功率(lv)(lv)的(de)(de)(de)(de)(de)計算(suan)公式p=ui，在(zai)(zai)四(si)個(ge)(ge)物理(li)(li)(li)量中只(zhi)要知(zhi)(zhi)道了其(qi)中的(de)(de)(de)(de)(de)兩個(ge)(ge)，就可(ke)(ke)以求出(chu)(chu)剩(sheng)余的(de)(de)(de)(de)(de)兩個(ge)(ge)物理(li)(li)(li)量；（有六種(zhong)情(qing)況）表(biao)(biao)格的(de)(de)(de)(de)(de)行(xing)(xing)，列出(chu)(chu)電(dian)(dian)(dian)(dian)流等物理(li)(li)(li)量在(zai)(zai)各分電(dian)(dian)(dian)(dian)路(lu)(lu)(lu)(lu)和(he)總(zong)(zong)電(dian)(dian)(dian)(dian)路(lu)(lu)(lu)(lu)的(de)(de)(de)(de)(de)數(shu)值，或物理(li)(li)(li)量在(zai)(zai)用(yong)電(dian)(dian)(dian)(dian)器(qi)的(de)(de)(de)(de)(de)各種(zhong)狀(zhuang)態下（如(ru)額定(ding)工作狀(zhuang)態、電(dian)(dian)(dian)(dian)路(lu)(lu)(lu)(lu)實(shi)際工作狀(zhuang)態）的(de)(de)(de)(de)(de)數(shu)值。而根據串、并(bing)聯(lian)電(dian)(dian)(dian)(dian)路(lu)(lu)(lu)(lu)特(te)點(dian)或根據題(ti)(ti)設，只(zhi)要知(zhi)(zhi)道其(qi)中兩個(ge)(ge)或一(yi)個(ge)(ge)，就可(ke)(ke)以求出(chu)(chu)剩(sheng)余的(de)(de)(de)(de)(de)物理(li)(li)(li)量，達到解(jie)(jie)決問(wen)題(ti)(ti)的(de)(de)(de)(de)(de)目的(de)(de)(de)(de)(de)。事實(shi)證(zheng)明(ming)，學(xue)(xue)(xue)生不斷(duan)積(ji)累歸納總(zong)(zong)結解(jie)(jie)題(ti)(ti)方(fang)法(fa)，有利于(yu)突破(po)重(zhong)點(dian)和(he)難點(dian)。

四(si)、和諧統一 遵循規律

篇6

題一：伏安法測電阻的(de)實驗(yan)中

(1)在右邊(bian)畫出(chu)電路圖 。

(2)伏安法測(ce)電(dian)阻的原理是(shi)根據______ 。

(3)滑動變阻器在電(dian)路中的作用(yong)是________。

(4)連接(jie)電路時，開關應(ying)________， 要求使(shi)用滑動(dong)變阻器(qi)的A接(jie)線柱，閉合開關前， 滑動(dong)變阻器(qi)的滑片P應(ying)滑到______，這是為了______________________ 。

題二：用如(ru)圖甲所示的(de)電(dian)(dian)路可以(yi)測(ce)量(liang)一(yi)個未知電(dian)(dian)阻的(de)阻值，其中Rx為(wei)待測(ce)電(dian)(dian)阻，R為(wei)電(dian)(dian)阻箱 ，S為(wei)單刀(dao)雙擲開關(guan)，R0為(wei)定(ding)值電(dian)(dian)阻。某同學(xue)用該(gai)電(dian)(dian)路進行實驗，主(zhu)要(yao)步驟有：

A.把開關S接b點，調(diao)節(jie)電阻箱，使電流表的示數為(wei)I

B.讀出電阻箱的示數R

C.把開關(guan)S接a點，讀出(chu)電流(liu)表的(de)示(shi)數為I

D.根據(ju)電路(lu)圖(tu)，連(lian)接實物，將電阻(zu)箱的阻(zu)值調至

(1)上(shang)述步驟的合理(li)順序是___________________ (只(zhi)需(xu)填(tian)寫(xie)序號)

(2)步驟A中電(dian)阻(zu)箱調節好后示(shi)數如圖乙(yi)所示(shi)，則它的示(shi)數為________ Ω.若已知R0的阻(zu)值(zhi)為10 Ω，則待測電(dian)阻(zu)的阻(zu)值(zhi)為 Ω.

(3)本實(shi)驗所采用的物理(li)思(si)想方法(fa)可稱為_____________(選填“控制變量法(fa)”或(huo)“等效替代(dai)法(fa)”)。

(4)若本(ben)次實驗中(zhong)將電流(liu)表(biao)換成電壓表(biao)，請你畫出電路圖。

金題精講

題一：小(xiao)樂想利用(yong)兩塊電(dian)(dian)流(liu)(liu)表和阻值已知的電(dian)(dian)阻R 0 測量(liang)電(dian)(dian)阻R x 的阻值。小(xiao)樂選擇了(le)滿足實(shi)驗要求的電(dian)(dian)源、電(dian)(dian)流(liu)(liu)表A1和A2，并(bing)連(lian)接(jie)了(le)部分實(shi)驗電(dian)(dian)路(lu)(lu)，如圖(tu)所(suo)示。(1)請(qing)(qing)你幫助小(xiao)樂完成圖(tu)所(suo)示的實(shi)驗電(dian)(dian)路(lu)(lu)的連(lian)接(jie)。(2)電(dian)(dian)流(liu)(liu)表A1的示數(shu)用(yong)I1表示，電(dian)(dian)流(liu)(liu)表A2的示數(shu)用(yong)I2表示，請(qing)(qing)用(yong)I1、I2和R0表示Rx.

R x = 。

題二：小龍想利用一塊(kuai)電壓表和阻值(zhi)已知(zhi)的(de)電阻R0測量(liang)電阻Rx的(de)阻值(zhi)。小龍選擇(ze)了滿足(zu)實(shi)驗要求的(de)器材。

(1)請你根(gen)據(ju)小(xiao)龍，并(bing)連接了(le)部分實驗電(dian)(dian)(dian)(dian)路(lu)，如圖所示。小(xiao)龍設(she)計(ji)的(de)實驗電(dian)(dian)(dian)(dian)路(lu)的(de)要求是(shi)：只閉合開關S和S1時(shi)，電(dian)(dian)(dian)(dian)壓(ya)表測量(liang)的(de)是(shi)電(dian)(dian)(dian)(dian)阻R0兩(liang)端的(de)電(dian)(dian)(dian)(dian)壓(ya)U1;只閉合開關S和S2時(shi)，電(dian)(dian)(dian)(dian)壓(ya)表測量(liang)的(de)是(shi)電(dian)(dian)(dian)(dian)源兩(liang)端的(de)電(dian)(dian)(dian)(dian)壓(ya)U2.

設(she)計要求只添加一根(gen)導線完成圖所示的(de)實驗電路的(de)連(lian)接;

(2)請你用U1、U2和R0表(biao)示(shi)出Rx，Rx=

思維拓展

題一：某校科技小組(zu)自制一臺(tai)可以測量電(dian)阻(zu)阻(zu)值(zhi)(zhi)的歐姆表。如圖所示，歐姆表電(dian)路(lu)由一只靈(ling)敏(min)電(dian)流(liu)表G，定(ding)值(zhi)(zhi)電(dian)阻(zu)R0、滑動(dong)變阻(zu)器和(he)干電(dian)池(設電(dian)壓(ya)不變)組(zu)成。使用時可把待測電(dian)阻(zu)接在(zai)A、B兩(liang)端。為(wei)了能(neng)直接從靈(ling)敏(min)電(dian)流(liu)表表盤(pan)(pan)上讀出A、B端接入的電(dian)阻(zu)的阻(zu)值(zhi)(zhi)，需(xu)在(zai)表盤(pan)(pan)上重新標注A、B間所測的電(dian)阻(zu)的阻(zu)值(zhi)(zhi)數(shu)。當將A、B兩(liang)端直接連接在(zai)一起時，調節滑動(dong)變阻(zu)器使靈(ling)敏(min)電(dian)流(liu)表指針偏(pian)轉到位置處(滿偏(pian))，已知此時靈(ling)敏(min)電(dian)流(liu)表內(nei)阻(zu)、滑動(dong)變阻(zu)器的有效(xiao)值(zhi)(zhi)和(he)定(ding)值(zhi)(zhi)電(dian)阻(zu)R0的總(zong)阻(zu)值(zhi)(zhi)為(wei)15Ω.問：

(1)在該歐姆表(biao)指針滿偏的位置處，盤(pan)面(mian)應(ying)標注的示(shi)數(shu)是多少?

(2)當(dang)A、B間斷開時(shi)，該歐姆表指針所(suo)指的位置處，盤面應標注(zhu)的示數是多(duo)少?

(3)該歐姆表(biao)表(biao)盤正中間位置處應標注(zhu)的示(shi)數(shu)是多(duo)少(shao)?簡要說明為什么。

 (4)該(gai)歐姆表(biao)表(biao)盤上(shang)(shang)的刻(ke)度值是(shi)否均勻?請從電(dian)路原理上(shang)(shang)說(shuo)明(ming)理由。

歐(ou)姆定(ding)律---測電阻(zu)問題

參考答案

重難點易錯點解析

題一：(2)

(3)保(bao)護電(dian)路(lu)、改(gai)變電(dian)路(lu)中的電(dian)流和電(dian)壓多次測量，取平均值(zhi)減小誤差

(4)斷開(kai)、阻值的地方(fang)、防止電(dian)(dian)路中電(dian)(dian)流過大。

題二(er)：(2)47，47 (3)等(deng)效替代法

思維拓展

篇7

關鍵詞(ci)：微課(ke)；初(chu)中物理；分(fen)層教學

微(wei)課(ke)對傳統教(jiao)學(xue)(xue)模式(shi)有(you)了很大的(de)(de)影響，微(wei)課(ke)具備(bei)短(duan)小(xiao)精(jing)悍和主題突出(chu)的(de)(de)特(te)點，初中物理教(jiao)師(shi)借助(zhu)微(wei)課(ke)的(de)(de)優(you)點開(kai)展分層教(jiao)學(xue)(xue)能(neng)夠有(you)效地提高教(jiao)學(xue)(xue)質(zhi)量(liang)。微(wei)課(ke)作為信息化教(jiao)學(xue)(xue)手段下的(de)(de)優(you)秀產(chan)物，能(neng)夠使(shi)教(jiao)學(xue)(xue)具備(bei)更高的(de)(de)質(zhi)量(liang)。在傳統的(de)(de)分層教(jiao)學(xue)(xue)中，教(jiao)師(shi)很難(nan)在一定的(de)(de)時間對學(xue)(xue)生(sheng)們(men)因(yin)材施教(jiao)，微(wei)課(ke)能(neng)夠幫助(zhu)教(jiao)師(shi)解(jie)決這(zhe)個棘(ji)手的(de)(de)問題。教(jiao)師(shi)將(jiang)課(ke)堂的(de)(de)重(zhong)難(nan)點錄制成(cheng)重(zhong)難(nan)點視頻，將(jiang)微(wei)課(ke)在學(xue)(xue)生(sheng)們(men)之間傳播學(xue)(xue)習，加(jia)深了學(xue)(xue)生(sheng)對知識的(de)(de)理解(jie)掌握，并(bing)且(qie)能(neng)夠有(you)效地促進學(xue)(xue)生(sheng)們(men)的(de)(de)自主學(xue)(xue)習能(neng)力。[1]

一、初中物(wu)理分層教學的(de)含義(yi)及原則

分層(ceng)(ceng)(ceng)教(jiao)(jiao)(jiao)(jiao)學(xue)(xue)(xue)(xue)(xue)(xue)屬于一種(zhong)因材施(shi)教(jiao)(jiao)(jiao)(jiao)的(de)教(jiao)(jiao)(jiao)(jiao)學(xue)(xue)(xue)(xue)(xue)(xue)方法。在(zai)初中(zhong)物理(li)分層(ceng)(ceng)(ceng)教(jiao)(jiao)(jiao)(jiao)學(xue)(xue)(xue)(xue)(xue)(xue)中(zhong)，教(jiao)(jiao)(jiao)(jiao)師需(xu)要根據所有(you)學(xue)(xue)(xue)(xue)(xue)(xue)生(sheng)的(de)學(xue)(xue)(xue)(xue)(xue)(xue)習(xi)能力以及差異(yi)性對不同層(ceng)(ceng)(ceng)次(ci)的(de)學(xue)(xue)(xue)(xue)(xue)(xue)生(sheng)進行不同的(de)教(jiao)(jiao)(jiao)(jiao)學(xue)(xue)(xue)(xue)(xue)(xue)指導(dao)。教(jiao)(jiao)(jiao)(jiao)師在(zai)分層(ceng)(ceng)(ceng)教(jiao)(jiao)(jiao)(jiao)學(xue)(xue)(xue)(xue)(xue)(xue)中(zhong)應(ying)該(gai)面向全(quan)體(ti)學(xue)(xue)(xue)(xue)(xue)(xue)生(sheng)，制定教(jiao)(jiao)(jiao)(jiao)學(xue)(xue)(xue)(xue)(xue)(xue)設計(ji)時需(xu)要考慮到學(xue)(xue)(xue)(xue)(xue)(xue)生(sheng)的(de)個(ge)(ge)體(ti)差異(yi)和(he)全(quan)面發展，讓(rang)每個(ge)(ge)學(xue)(xue)(xue)(xue)(xue)(xue)生(sheng)都能夠在(zai)物理(li)學(xue)(xue)(xue)(xue)(xue)(xue)習(xi)達到知識飽和(he)的(de)狀態。另外，初中(zhong)物理(li)教(jiao)(jiao)(jiao)(jiao)師在(zai)教(jiao)(jiao)(jiao)(jiao)學(xue)(xue)(xue)(xue)(xue)(xue)中(zhong)應(ying)該(gai)堅持學(xue)(xue)(xue)(xue)(xue)(xue)生(sheng)的(de)主體(ti)性原(yuan)則，將學(xue)(xue)(xue)(xue)(xue)(xue)生(sheng)們(men)作(zuo)為課(ke)堂(tang)主體(ti)，在(zai)分層(ceng)(ceng)(ceng)教(jiao)(jiao)(jiao)(jiao)學(xue)(xue)(xue)(xue)(xue)(xue)中(zhong)根據每個(ge)(ge)層(ceng)(ceng)(ceng)次(ci)的(de)學(xue)(xue)(xue)(xue)(xue)(xue)生(sheng)們(men)開展適合性的(de)教(jiao)(jiao)(jiao)(jiao)學(xue)(xue)(xue)(xue)(xue)(xue)指導(dao)，促進學(xue)(xue)(xue)(xue)(xue)(xue)生(sheng)們(men)的(de)學(xue)(xue)(xue)(xue)(xue)(xue)習(xi)能力得以提升，激發學(xue)(xue)(xue)(xue)(xue)(xue)生(sheng)學(xue)(xue)(xue)(xue)(xue)(xue)習(xi)物理(li)的(de)興趣和(he)熱情(qing)。

二(er)、微課(ke)構(gou)建初中物理分層教學的(de)必要性

（一）微課促進(jin)分(fen)(fen)層教(jiao)(jiao)學(xue)微課教(jiao)(jiao)學(xue)能(neng)(neng)夠有效促進(jin)學(xue)生(sheng)對物理(li)知識的吸收(shou)，初中(zhong)物理(li)教(jiao)(jiao)師(shi)在(zai)教(jiao)(jiao)學(xue)中(zhong)開展分(fen)(fen)層教(jiao)(jiao)學(xue)，微課的引入(ru)能(neng)(neng)夠解決分(fen)(fen)層教(jiao)(jiao)學(xue)中(zhong)的時(shi)間限制(zhi)，使分(fen)(fen)層教(jiao)(jiao)學(xue)更(geng)加高效。教(jiao)(jiao)師(shi)在(zai)教(jiao)(jiao)學(xue)中(zhong)需要避免微效勞動，在(zai)教(jiao)(jiao)學(xue)中(zhong)考慮全體(ti)學(xue)生(sheng)的情況進(jin)行微課制(zhi)作(zuo)，提升物理(li)教(jiao)(jiao)學(xue)質量(liang)。

（二）微課解決個體差異(yi)初中生(sheng)(sheng)之(zhi)間具(ju)備著一(yi)定的(de)(de)學(xue)(xue)(xue)習(xi)差異(yi)，每(mei)個人的(de)(de)學(xue)(xue)(xue)習(xi)認知能(neng)力不盡相同，教(jiao)(jiao)師在教(jiao)(jiao)學(xue)(xue)(xue)中需(xu)要重(zhong)(zhong)視學(xue)(xue)(xue)生(sheng)(sheng)們(men)的(de)(de)差異(yi)。微課視頻能(neng)夠讓每(mei)個學(xue)(xue)(xue)生(sheng)(sheng)在學(xue)(xue)(xue)習(xi)中根(gen)據自己薄弱的(de)(de)知識進(jin)行補(bu)習(xi)，有(you)效的(de)(de)解決了學(xue)(xue)(xue)生(sheng)(sheng)之(zhi)間存在的(de)(de)個體差異(yi)。教(jiao)(jiao)師在借(jie)助微課構建分層教(jiao)(jiao)學(xue)(xue)(xue)時需(xu)要關注每(mei)個學(xue)(xue)(xue)生(sheng)(sheng)，尊重(zhong)(zhong)學(xue)(xue)(xue)生(sheng)(sheng)們(men)的(de)(de)差異(yi)，對每(mei)個學(xue)(xue)(xue)生(sheng)(sheng)適當的(de)(de)鼓勵，讓學(xue)(xue)(xue)生(sheng)(sheng)們(men)能(neng)夠拉(la)近彼此之(zhi)間的(de)(de)距離(li)。

（三）微(wei)課(ke)符(fu)合(he)因材施教(jiao)在(zai)新(xin)(xin)(xin)課(ke)程目標改革的(de)(de)(de)背(bei)景下(xia)(xia)，很多初中物理(li)教(jiao)師(shi)在(zai)課(ke)堂上(shang)會迫于引進新(xin)(xin)(xin)型的(de)(de)(de)教(jiao)學(xue)方(fang)式，教(jiao)師(shi)在(zai)分(fen)層教(jiao)學(xue)中對新(xin)(xin)(xin)型教(jiao)學(xue)模式不太熟練，所以(yi)會出(chu)現顧此(ci)失彼(bi)的(de)(de)(de)現象(xiang)。因此(ci)，微(wei)課(ke)構建(jian)的(de)(de)(de)分(fen)層教(jiao)學(xue)符(fu)合(he)了(le)(le)當下(xia)(xia)因材施教(jiao)的(de)(de)(de)教(jiao)學(xue)理(li)念(nian)，教(jiao)師(shi)在(zai)課(ke)前錄制(zhi)微(wei)課(ke)視頻，減(jian)少了(le)(le)課(ke)堂的(de)(de)(de)慌亂，并且(qie)能(neng)夠利用微(wei)課(ke)隨機(ji)應變每(mei)個(ge)(ge)學(xue)生(sheng)提(ti)出(chu)的(de)(de)(de)問題，使得每(mei)個(ge)(ge)學(xue)生(sheng)都能(neng)夠充分(fen)發揮自身(shen)的(de)(de)(de)潛(qian)能(neng)。

三、微課構(gou)建初(chu)中物理分層(ceng)教學的策略

（一(yi)）針(zhen)對學(xue)(xue)(xue)生(sheng)(sheng)(sheng)(sheng)(sheng)情(qing)況(kuang)進行分層(ceng)微(wei)(wei)(wei)課(ke)(ke)(ke)(ke)作為信息化背景下有(you)(you)(you)效的(de)(de)(de)(de)(de)(de)(de)教(jiao)(jiao)(jiao)(jiao)學(xue)(xue)(xue)資源，初中物(wu)(wu)理教(jiao)(jiao)(jiao)(jiao)師(shi)(shi)應該充(chong)分利(li)用微(wei)(wei)(wei)課(ke)(ke)(ke)(ke)的(de)(de)(de)(de)(de)(de)(de)優勢將(jiang)多樣(yang)(yang)性(xing)的(de)(de)(de)(de)(de)(de)(de)課(ke)(ke)(ke)(ke)本內容進行分層(ceng)，多樣(yang)(yang)化的(de)(de)(de)(de)(de)(de)(de)微(wei)(wei)(wei)課(ke)(ke)(ke)(ke)資源能(neng)(neng)夠(gou)(gou)根(gen)據學(xue)(xue)(xue)生(sheng)(sheng)(sheng)(sheng)(sheng)們(men)(men)的(de)(de)(de)(de)(de)(de)(de)特(te)點完成(cheng)合理分配(pei)。教(jiao)(jiao)(jiao)(jiao)師(shi)(shi)在(zai)設(she)計微(wei)(wei)(wei)課(ke)(ke)(ke)(ke)時(shi)(shi)需要(yao)面向全體學(xue)(xue)(xue)生(sheng)(sheng)(sheng)(sheng)(sheng)，根(gen)據學(xue)(xue)(xue)生(sheng)(sheng)(sheng)(sheng)(sheng)們(men)(men)的(de)(de)(de)(de)(de)(de)(de)個(ge)人情(qing)況(kuang)能(neng)(neng)夠(gou)(gou)更好(hao)進行微(wei)(wei)(wei)課(ke)(ke)(ke)(ke)資源整(zheng)理分配(pei)。另外，每(mei)個(ge)學(xue)(xue)(xue)生(sheng)(sheng)(sheng)(sheng)(sheng)在(zai)選擇鞏(gong)固知(zhi)識的(de)(de)(de)(de)(de)(de)(de)微(wei)(wei)(wei)課(ke)(ke)(ke)(ke)時(shi)(shi)同樣(yang)(yang)需要(yao)對自身情(qing)況(kuang)進行充(chong)分的(de)(de)(de)(de)(de)(de)(de)了解(jie)(jie)。班級內總會(hui)(hui)出現(xian)(xian)很刻苦(ku)的(de)(de)(de)(de)(de)(de)(de)學(xue)(xue)(xue)生(sheng)(sheng)(sheng)(sheng)(sheng)但是最終(zhong)成(cheng)績始終(zhong)不(bu)理想(xiang)，這(zhe)是由于(yu)學(xue)(xue)(xue)生(sheng)(sheng)(sheng)(sheng)(sheng)們(men)(men)沒有(you)(you)(you)找到(dao)適合自己的(de)(de)(de)(de)(de)(de)(de)學(xue)(xue)(xue)習(xi)方法，教(jiao)(jiao)(jiao)(jiao)師(shi)(shi)在(zai)這(zhe)時(shi)(shi)可(ke)以憑借豐(feng)富(fu)的(de)(de)(de)(de)(de)(de)(de)教(jiao)(jiao)(jiao)(jiao)學(xue)(xue)(xue)經驗(yan)幫助(zhu)學(xue)(xue)(xue)生(sheng)(sheng)(sheng)(sheng)(sheng)分析學(xue)(xue)(xue)習(xi)情(qing)況(kuang)，使教(jiao)(jiao)(jiao)(jiao)學(xue)(xue)(xue)足夠(gou)(gou)公平公正。例如：在(zai)學(xue)(xue)(xue)生(sheng)(sheng)(sheng)(sheng)(sheng)們(men)(men)學(xue)(xue)(xue)習(xi)九年(nian)(nian)級物(wu)(wu)理上冊第十(shi)二章《動能(neng)(neng)勢能(neng)(neng)機械能(neng)(neng)》的(de)(de)(de)(de)(de)(de)(de)過程(cheng)中，教(jiao)(jiao)(jiao)(jiao)師(shi)(shi)可(ke)以在(zai)課(ke)(ke)(ke)(ke)前針(zhen)對每(mei)組學(xue)(xue)(xue)生(sheng)(sheng)(sheng)(sheng)(sheng)的(de)(de)(de)(de)(de)(de)(de)學(xue)(xue)(xue)習(xi)能(neng)(neng)力(li)進行分析。動能(neng)(neng)、重力(li)勢能(neng)(neng)、彈性(xing)勢能(neng)(neng)的(de)(de)(de)(de)(de)(de)(de)初步概念在(zai)八年(nian)(nian)級的(de)(de)(de)(de)(de)(de)(de)教(jiao)(jiao)(jiao)(jiao)學(xue)(xue)(xue)中已(yi)經出現(xian)(xian)了，教(jiao)(jiao)(jiao)(jiao)師(shi)(shi)可(ke)以站在(zai)所有(you)(you)(you)學(xue)(xue)(xue)生(sheng)(sheng)(sheng)(sheng)(sheng)的(de)(de)(de)(de)(de)(de)(de)角度上設(she)計一(yi)些微(wei)(wei)(wei)課(ke)(ke)(ke)(ke)視(shi)頻。在(zai)課(ke)(ke)(ke)(ke)堂上，教(jiao)(jiao)(jiao)(jiao)師(shi)(shi)將(jiang)視(shi)頻共分為三步，學(xue)(xue)(xue)生(sheng)(sheng)(sheng)(sheng)(sheng)們(men)(men)集體觀(guan)(guan)看關(guan)于(yu)運(yun)動的(de)(de)(de)(de)(de)(de)(de)物(wu)(wu)體能(neng)(neng)做功和具(ju)有(you)(you)(you)動能(neng)(neng)的(de)(de)(de)(de)(de)(de)(de)實例分析，這(zhe)對于(yu)有(you)(you)(you)八年(nian)(nian)級基(ji)礎(chu)的(de)(de)(de)(de)(de)(de)(de)學(xue)(xue)(xue)生(sheng)(sheng)(sheng)(sheng)(sheng)是容易(yi)理解(jie)(jie)的(de)(de)(de)(de)(de)(de)(de)。教(jiao)(jiao)(jiao)(jiao)師(shi)(shi)讓學(xue)(xue)(xue)生(sheng)(sheng)(sheng)(sheng)(sheng)們(men)(men)集體欣賞2008年(nian)(nian)北(bei)京奧運(yun)會(hui)(hui)蹦床比賽的(de)(de)(de)(de)(de)(de)(de)精彩瞬間，這(zhe)時(shi)(shi)會(hui)(hui)有(you)(you)(you)學(xue)(xue)(xue)生(sheng)(sheng)(sheng)(sheng)(sheng)提(ti)出不(bu)同的(de)(de)(de)(de)(de)(de)(de)問題(ti)(ti)，教(jiao)(jiao)(jiao)(jiao)師(shi)(shi)根(gen)據學(xue)(xue)(xue)生(sheng)(sheng)(sheng)(sheng)(sheng)觀(guan)(guan)看微(wei)(wei)(wei)課(ke)(ke)(ke)(ke)視(shi)頻的(de)(de)(de)(de)(de)(de)(de)反(fan)應情(qing)況(kuang)針(zhen)對性(xing)的(de)(de)(de)(de)(de)(de)(de)提(ti)問學(xue)(xue)(xue)生(sheng)(sheng)(sheng)(sheng)(sheng)，并(bing)且進行詳細講(jiang)解(jie)(jie)。對于(yu)其(qi)他在(zai)預(yu)習(xi)中有(you)(you)(you)了一(yi)定知(zhi)識基(ji)礎(chu)的(de)(de)(de)(de)(de)(de)(de)學(xue)(xue)(xue)生(sheng)(sheng)(sheng)(sheng)(sheng)，教(jiao)(jiao)(jiao)(jiao)師(shi)(shi)可(ke)以讓這(zhe)些同學(xue)(xue)(xue)先觀(guan)(guan)察演示實驗(yan)的(de)(de)(de)(de)(de)(de)(de)視(shi)頻。這(zhe)樣(yang)(yang)一(yi)來，學(xue)(xue)(xue)生(sheng)(sheng)(sheng)(sheng)(sheng)們(men)(men)在(zai)一(yi)起互(hu)(hu)幫互(hu)(hu)助(zhu)能(neng)(neng)夠(gou)(gou)發(fa)現(xian)(xian)問題(ti)(ti)并(bing)且通(tong)過教(jiao)(jiao)(jiao)(jiao)師(shi)(shi)的(de)(de)(de)(de)(de)(de)(de)引導完成(cheng)知(zhi)識認知(zhi)，所有(you)(you)(you)的(de)(de)(de)(de)(de)(de)(de)學(xue)(xue)(xue)生(sheng)(sheng)(sheng)(sheng)(sheng)都可(ke)以學(xue)(xue)(xue)到(dao)新的(de)(de)(de)(de)(de)(de)(de)知(zhi)識。每(mei)個(ge)學(xue)(xue)(xue)生(sheng)(sheng)(sheng)(sheng)(sheng)在(zai)課(ke)(ke)(ke)(ke)堂上體驗(yan)到(dao)學(xue)(xue)(xue)習(xi)的(de)(de)(de)(de)(de)(de)(de)樂趣和成(cheng)就感，有(you)(you)(you)助(zhu)于(yu)學(xue)(xue)(xue)生(sheng)(sheng)(sheng)(sheng)(sheng)語言(yan)表達能(neng)(neng)力(li)的(de)(de)(de)(de)(de)(de)(de)提(ti)升。[2]

（二）針對教(jiao)(jiao)學(xue)(xue)(xue)(xue)(xue)目標進(jin)行(xing)分層初中(zhong)(zhong)物理(li)教(jiao)(jiao)師(shi)(shi)在分層教(jiao)(jiao)學(xue)(xue)(xue)(xue)(xue)中(zhong)(zhong)利用(yong)微(wei)(wei)課(ke)(ke)(ke)(ke)著(zhu)力營造出(chu)民主(zhu)和諧的(de)(de)(de)(de)(de)(de)課(ke)(ke)(ke)(ke)堂氛圍，學(xue)(xue)(xue)(xue)(xue)生(sheng)(sheng)(sheng)們可(ke)(ke)以(yi)(yi)在自(zi)(zi)己(ji)的(de)(de)(de)(de)(de)(de)認知(zhi)能(neng)力基(ji)礎上相互評價課(ke)(ke)(ke)(ke)堂學(xue)(xue)(xue)(xue)(xue)習的(de)(de)(de)(de)(de)(de)內容。微(wei)(wei)課(ke)(ke)(ke)(ke)作為一(yi)(yi)(yi)(yi)(yi)個網絡學(xue)(xue)(xue)(xue)(xue)習軟件，使用(yong)微(wei)(wei)課(ke)(ke)(ke)(ke)的(de)(de)(de)(de)(de)(de)群體(ti)相對比(bi)較廣(guang)泛。盡管有些(xie)(xie)學(xue)(xue)(xue)(xue)(xue)生(sheng)(sheng)(sheng)能(neng)夠(gou)準確的(de)(de)(de)(de)(de)(de)認識(shi)到自(zi)(zi)己(ji)的(de)(de)(de)(de)(de)(de)學(xue)(xue)(xue)(xue)(xue)習狀況，但是選擇適合自(zi)(zi)己(ji)的(de)(de)(de)(de)(de)(de)微(wei)(wei)課(ke)(ke)(ke)(ke)也(ye)(ye)不(bu)(bu)是一(yi)(yi)(yi)(yi)(yi)件易事。這(zhe)時，初中(zhong)(zhong)物理(li)教(jiao)(jiao)師(shi)(shi)需要充分發揮自(zi)(zi)己(ji)的(de)(de)(de)(de)(de)(de)引(yin)導(dao)作用(yong)，根(gen)(gen)據(ju)教(jiao)(jiao)學(xue)(xue)(xue)(xue)(xue)目標設計不(bu)(bu)同(tong)難度的(de)(de)(de)(de)(de)(de)微(wei)(wei)課(ke)(ke)(ke)(ke)，幫助學(xue)(xue)(xue)(xue)(xue)生(sheng)(sheng)(sheng)過濾掉一(yi)(yi)(yi)(yi)(yi)些(xie)(xie)無(wu)用(yong)的(de)(de)(de)(de)(de)(de)微(wei)(wei)課(ke)(ke)(ke)(ke)，促(cu)進(jin)每個學(xue)(xue)(xue)(xue)(xue)生(sheng)(sheng)(sheng)能(neng)夠(gou)提高學(xue)(xue)(xue)(xue)(xue)習質量和自(zi)(zi)身(shen)綜(zong)合素質。另外(wai)，教(jiao)(jiao)師(shi)(shi)也(ye)(ye)可(ke)(ke)以(yi)(yi)針對自(zi)(zi)己(ji)班級學(xue)(xue)(xue)(xue)(xue)習情況，在課(ke)(ke)(ke)(ke)堂結(jie)束(shu)之(zhi)后為學(xue)(xue)(xue)(xue)(xue)生(sheng)(sheng)(sheng)制作鞏固型微(wei)(wei)課(ke)(ke)(ke)(ke)，實現(xian)物理(li)學(xue)(xue)(xue)(xue)(xue)科教(jiao)(jiao)學(xue)(xue)(xue)(xue)(xue)中(zhong)(zhong)理(li)論和過程(cheng)的(de)(de)(de)(de)(de)(de)有機整合。例如：在學(xue)(xue)(xue)(xue)(xue)生(sheng)(sheng)(sheng)們學(xue)(xue)(xue)(xue)(xue)習九年級物理(li)上冊第十四章《歐(ou)姆定(ding)律》的(de)(de)(de)(de)(de)(de)過程(cheng)中(zhong)(zhong)，教(jiao)(jiao)師(shi)(shi)可(ke)(ke)以(yi)(yi)利用(yong)三個難度等(deng)級不(bu)(bu)同(tong)的(de)(de)(de)(de)(de)(de)微(wei)(wei)課(ke)(ke)(ke)(ke)。教(jiao)(jiao)師(shi)(shi)在上課(ke)(ke)(ke)(ke)前將(jiang)教(jiao)(jiao)學(xue)(xue)(xue)(xue)(xue)目標進(jin)行(xing)分層，教(jiao)(jiao)師(shi)(shi)首先利用(yong)微(wei)(wei)課(ke)(ke)(ke)(ke)帶(dai)領學(xue)(xue)(xue)(xue)(xue)生(sheng)(sheng)(sheng)復(fu)習電(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)、電(dian)(dian)(dian)(dian)(dian)(dian)壓、電(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)的(de)(de)(de)(de)(de)(de)基(ji)本知(zhi)識(shi)和電(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)大小的(de)(de)(de)(de)(de)(de)影響(xiang)因素，提問學(xue)(xue)(xue)(xue)(xue)生(sheng)(sheng)(sheng)思考電(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)、電(dian)(dian)(dian)(dian)(dian)(dian)壓和電(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)之(zhi)間的(de)(de)(de)(de)(de)(de)聯系(xi)(xi)。教(jiao)(jiao)師(shi)(shi)引(yin)導(dao)學(xue)(xue)(xue)(xue)(xue)生(sheng)(sheng)(sheng)根(gen)(gen)據(ju)“讓小燈(deng)泡變亮”猜想它們之(zhi)間的(de)(de)(de)(de)(de)(de)關(guan)系(xi)(xi)，引(yin)出(chu)歐(ou)姆定(ding)律。教(jiao)(jiao)師(shi)(shi)給出(chu)學(xue)(xue)(xue)(xue)(xue)生(sheng)(sheng)(sheng)思考探究的(de)(de)(de)(de)(de)(de)時間，學(xue)(xue)(xue)(xue)(xue)生(sheng)(sheng)(sheng)們一(yi)(yi)(yi)(yi)(yi)起根(gen)(gen)據(ju)微(wei)(wei)課(ke)(ke)(ke)(ke)提供(gong)的(de)(de)(de)(de)(de)(de)歐(ou)姆定(ding)律講解(jie)研(yan)究實驗(yan)，根(gen)(gen)據(ju)微(wei)(wei)課(ke)(ke)(ke)(ke)展示的(de)(de)(de)(de)(de)(de)實驗(yan)視頻記錄分析數據(ju)，得出(chu)電(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)與電(dian)(dian)(dian)(dian)(dian)(dian)壓之(zhi)間的(de)(de)(de)(de)(de)(de)關(guan)系(xi)(xi)；教(jiao)(jiao)師(shi)(shi)利用(yong)微(wei)(wei)課(ke)(ke)(ke)(ke)轉向下一(yi)(yi)(yi)(yi)(yi)個環節(jie)，再次讓學(xue)(xue)(xue)(xue)(xue)生(sheng)(sheng)(sheng)根(gen)(gen)據(ju)微(wei)(wei)課(ke)(ke)(ke)(ke)實驗(yan)探究得出(chu)電(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)與電(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)的(de)(de)(de)(de)(de)(de)關(guan)系(xi)(xi)。在這(zhe)樣的(de)(de)(de)(de)(de)(de)教(jiao)(jiao)學(xue)(xue)(xue)(xue)(xue)過程(cheng)中(zhong)(zhong)，教(jiao)(jiao)師(shi)(shi)需要引(yin)導(dao)學(xue)(xue)(xue)(xue)(xue)生(sheng)(sheng)(sheng)探究的(de)(de)(de)(de)(de)(de)方向，將(jiang)微(wei)(wei)課(ke)(ke)(ke)(ke)作為輔助教(jiao)(jiao)學(xue)(xue)(xue)(xue)(xue)工具(ju)。當(dang)學(xue)(xue)(xue)(xue)(xue)生(sheng)(sheng)(sheng)們對本節(jie)課(ke)(ke)(ke)(ke)的(de)(de)(de)(de)(de)(de)知(zhi)識(shi)有了一(yi)(yi)(yi)(yi)(yi)定(ding)的(de)(de)(de)(de)(de)(de)掌(zhang)握之(zhi)后，學(xue)(xue)(xue)(xue)(xue)生(sheng)(sheng)(sheng)根(gen)(gen)據(ju)微(wei)(wei)課(ke)(ke)(ke)(ke)提供(gong)的(de)(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)壓、電(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)和電(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)的(de)(de)(de)(de)(de)(de)簡單(dan)問題(ti)進(jin)行(xing)歐(ou)姆定(ding)律應用(yong)，微(wei)(wei)課(ke)(ke)(ke)(ke)中(zhong)(zhong)需要重(zhong)點提示學(xue)(xue)(xue)(xue)(xue)生(sheng)(sheng)(sheng)做(zuo)題(ti)的(de)(de)(de)(de)(de)(de)模板，培養學(xue)(xue)(xue)(xue)(xue)生(sheng)(sheng)(sheng)養成解(jie)答電(dian)(dian)(dian)(dian)(dian)(dian)學(xue)(xue)(xue)(xue)(xue)問題(ti)的(de)(de)(de)(de)(de)(de)良好習慣，形成規范解(jie)答問題(ti)的(de)(de)(de)(de)(de)(de)能(neng)力。

（三）針對課(ke)(ke)(ke)堂(tang)時(shi)間進(jin)行分(fen)層微(wei)課(ke)(ke)(ke)的(de)顯(xian)著(zhu)特點(dian)就是不(bu)受(shou)到時(shi)間的(de)限制，在(zai)(zai)以往的(de)初中物理(li)教(jiao)學(xue)(xue)(xue)中，教(jiao)師(shi)會因為上(shang)課(ke)(ke)(ke)時(shi)間有(you)限沒有(you)及(ji)時(shi)解(jie)(jie)決(jue)學(xue)(xue)(xue)生(sheng)在(zai)(zai)課(ke)(ke)(ke)堂(tang)上(shang)沒有(you)理(li)解(jie)(jie)的(de)問題(ti)，學(xue)(xue)(xue)生(sheng)在(zai)(zai)課(ke)(ke)(ke)后也(ye)無法得到教(jiao)師(shi)的(de)復(fu)習指導，導致積攢的(de)物理(li)問題(ti)越來越多，造成學(xue)(xue)(xue)習效果很不(bu)理(li)想。在(zai)(zai)新課(ke)(ke)(ke)程(cheng)目標改革的(de)背景(jing)下，教(jiao)師(shi)可以借助微(wei)課(ke)(ke)(ke)在(zai)(zai)課(ke)(ke)(ke)前錄制好(hao)本節重難(nan)點(dian)知識(shi)(shi)講解(jie)(jie)的(de)視頻或者(zhe)視頻，在(zai)(zai)課(ke)(ke)(ke)堂(tang)上(shang)降低學(xue)(xue)(xue)生(sheng)學(xue)(xue)(xue)習的(de)緊(jin)迫感，學(xue)(xue)(xue)生(sheng)們在(zai)(zai)課(ke)(ke)(ke)下能夠根據自(zi)己(ji)的(de)實際(ji)情(qing)況(kuang)進(jin)行查漏補缺。另外(wai)，教(jiao)師(shi)在(zai)(zai)課(ke)(ke)(ke)堂(tang)上(shang)借助微(wei)課(ke)(ke)(ke)對學(xue)(xue)(xue)生(sheng)們進(jin)行實驗指導，學(xue)(xue)(xue)生(sheng)們能夠清晰明(ming)了的(de)觀(guan)看到注(zhu)意(yi)事項，對知識(shi)(shi)的(de)理(li)解(jie)(jie)會更進(jin)一步(bu)。

例如：在(zai)學(xue)(xue)(xue)(xue)生(sheng)們學(xue)(xue)(xue)(xue)習九年級物(wu)理(li)上(shang)冊第(di)十四章《電阻(zu)》的(de)過程(cheng)中，教師可以(yi)借(jie)助微(wei)課(ke)(ke)(ke)錄制(zhi)電阻(zu)實(shi)(shi)(shi)驗(yan)(yan)視頻(pin)(pin)避免實(shi)(shi)(shi)際操作(zuo)的(de)危(wei)險問題。由(you)于《電阻(zu)》是一節以(yi)實(shi)(shi)(shi)驗(yan)(yan)活(huo)動為主(zhu)的(de)新課(ke)(ke)(ke)，學(xue)(xue)(xue)(xue)生(sheng)對物(wu)理(li)實(shi)(shi)(shi)驗(yan)(yan)本身就有(you)(you)探究欲望，教師可以(yi)讓(rang)學(xue)(xue)(xue)(xue)生(sheng)們在(zai)課(ke)(ke)(ke)堂(tang)上(shang)提前觀看(kan)實(shi)(shi)(shi)驗(yan)(yan)操作(zuo)，學(xue)(xue)(xue)(xue)生(sheng)學(xue)(xue)(xue)(xue)會儀器的(de)安裝(zhuang)整理(li)和故障(zhang)分析(xi)之(zhi)后再進入(ru)實(shi)(shi)(shi)際操作(zuo)能(neng)夠更加(jia)有(you)(you)助于創新性思維的(de)發(fa)揮。很多學(xue)(xue)(xue)(xue)生(sheng)會不明白電阻(zu)物(wu)理(li)實(shi)(shi)(shi)驗(yan)(yan)設計的(de)思維方法，學(xue)(xue)(xue)(xue)生(sheng)們就可以(yi)在(zai)實(shi)(shi)(shi)驗(yan)(yan)操作(zuo)之(zhi)前在(zai)課(ke)(ke)(ke)下將微(wei)課(ke)(ke)(ke)視頻(pin)(pin)再次觀看(kan)，確(que)保實(shi)(shi)(shi)驗(yan)(yan)過程(cheng)的(de)準確(que)。這樣(yang)一來(lai)，學(xue)(xue)(xue)(xue)生(sheng)們會在(zai)課(ke)(ke)(ke)堂(tang)上(shang)激發(fa)內心(xin)實(shi)(shi)(shi)驗(yan)(yan)探究的(de)熱情，并且能(neng)夠借(jie)助微(wei)課(ke)(ke)(ke)反(fan)復(fu)鞏固(gu)實(shi)(shi)(shi)驗(yan)(yan)知識(shi)防(fang)止(zhi)出(chu)錯。[3]

（一）針(zhen)對課后(hou)作(zuo)業(ye)進行(xing)分(fen)層(ceng)課后(hou)作(zuo)業(ye)是學(xue)(xue)(xue)(xue)(xue)(xue)生(sheng)學(xue)(xue)(xue)(xue)(xue)(xue)習(xi)物(wu)理(li)中的(de)(de)重(zhong)要(yao)環節，每(mei)個學(xue)(xue)(xue)(xue)(xue)(xue)生(sheng)在課堂上(shang)的(de)(de)知識接收程(cheng)度不同(tong)。因此，微課構建分(fen)層(ceng)課后(hou)作(zuo)業(ye)成(cheng)為(wei)了(le)每(mei)個學(xue)(xue)(xue)(xue)(xue)(xue)生(sheng)學(xue)(xue)(xue)(xue)(xue)(xue)習(xi)的(de)(de)重(zhong)要(yao)工(gong)具(ju)，教師在學(xue)(xue)(xue)(xue)(xue)(xue)生(sheng)們學(xue)(xue)(xue)(xue)(xue)(xue)習(xi)完新課之(zhi)后(hou)可以(yi)(yi)制(zhi)定多(duo)個層(ceng)次的(de)(de)課后(hou)作(zuo)用，讓(rang)作(zuo)業(ye)成(cheng)為(wei)每(mei)個學(xue)(xue)(xue)(xue)(xue)(xue)生(sheng)延伸課堂知識的(de)(de)工(gong)具(ju)。例如(ru)：在學(xue)(xue)(xue)(xue)(xue)(xue)生(sheng)們學(xue)(xue)(xue)(xue)(xue)(xue)習(xi)了(le)九年(nian)級物(wu)理(li)上(shang)冊第(di)十一章《機(ji)械功率》之(zhi)后(hou)，教師可以(yi)(yi)針(zhen)對不同(tong)層(ceng)次的(de)(de)學(xue)(xue)(xue)(xue)(xue)(xue)生(sheng)制(zhi)定必做題和(he)選做題，學(xue)(xue)(xue)(xue)(xue)(xue)生(sheng)們會根據自己(ji)的(de)(de)實際情況選擇作(zuo)業(ye)，這樣的(de)(de)作(zuo)業(ye)形(xing)式會讓(rang)每(mei)個學(xue)(xue)(xue)(xue)(xue)(xue)生(sheng)都獲(huo)得成(cheng)功的(de)(de)喜悅。

四、結束語

 總(zong)而(er)言(yan)之(zhi)，微(wei)課對于初(chu)中物理分層教(jiao)(jiao)學(xue)有著十分重要的(de)作用，教(jiao)(jiao)師(shi)應該合理利用微(wei)課促進分層教(jiao)(jiao)學(xue)的(de)質量。初(chu)中物理對于學(xue)生(sheng)(sheng)(sheng)們(men)來說只是學(xue)習(xi)的(de)開始，同樣是初(chu)中生(sheng)(sheng)(sheng)思(si)維發展的(de)關鍵時期，教(jiao)(jiao)師(shi)通過微(wei)課構建的(de)分層教(jiao)(jiao)學(xue)能(neng)夠幫助學(xue)生(sheng)(sheng)(sheng)強(qiang)化知識點(dian)的(de)理解(jie)，徹底打破(po)傳統的(de)教(jiao)(jiao)學(xue)方式在，在教(jiao)(jiao)學(xue)中根據微(wei)課讓物理更加具備溫(wen)度，讓學(xue)生(sheng)(sheng)(sheng)能(neng)夠更好地提升自(zi)己。[4]

參考文獻

[1]李化榮.提升初(chu)中物理課堂教學效率的(de)策(ce)略[J].天天愛科學(教育(yu)前沿),2018(12).

[2]陳剛.微課模式(shi)在初中(zhong)物理課堂教學中(zhong)的運用[J].新(xin)課程(cheng)(中(zhong)學),2018(10).

[3]劉亮.提高初中物理課堂(tang)教學效率的探究[J].中學課程輔(fu)導(教師教育),2017(24).

篇8

不管是出(chu)于外因(yin)，還是內因(yin)，初中生都覺得(de)電學(xue)(xue)知識(shi)學(xue)(xue)起來(lai)比較(jiao)困(kun)難.如何改變(bian)這一(yi)現象呢？

本(ben)文針對初中物理(li)中的電學(xue)知識的學(xue)習展開論述，希望可以提高學(xue)生電學(xue)部分的學(xue)習效率.

一、打牢基礎

九層之臺(tai)，起于壘土.再(zai)好的學(xue)(xue)習成績(ji)，也要建立(li)在基礎知(zhi)識(shi)之上.物理(li)教學(xue)(xue)中的電學(xue)(xue)基礎知(zhi)識(shi)主要是指基本(ben)概念和規(gui)律，只有牢(lao)固地(di)掌握這些(xie)(xie)基本(ben)概念和規(gui)律，才能熟練地(di)運用這些(xie)(xie)概念和規(gui)律解決遇到的問(wen)題，進行簡單的判(pan)斷、推理(li)和計算.

例如(ru)，電(dian)(dian)(dian)(dian)(dian)學(xue)中(zhong)的(de)(de)概念包(bao)含了電(dian)(dian)(dian)(dian)(dian)流強度(du)、電(dian)(dian)(dian)(dian)(dian)壓、電(dian)(dian)(dian)(dian)(dian)阻、電(dian)(dian)(dian)(dian)(dian)功、電(dian)(dian)(dian)(dian)(dian)功率、磁感(gan)線等(deng)，這些(xie)(xie)都是(shi)電(dian)(dian)(dian)(dian)(dian)學(xue)基(ji)礎知(zhi)識(shi)中(zhong)最(zui)基(ji)礎的(de)(de)內容.還有電(dian)(dian)(dian)(dian)(dian)學(xue)中(zhong)的(de)(de)一(yi)些(xie)(xie)規律(lv)(lv)：歐姆定(ding)律(lv)(lv)、焦耳(er)定(ding)律(lv)(lv)和串、并聯電(dian)(dian)(dian)(dian)(dian)路的(de)(de)特點(dian)等(deng)，也(ye)是(shi)最(zui)基(ji)礎的(de)(de)內容.這些(xie)(xie)內容如(ru)果掌握(wo)不牢，那么(me)勢必在做(zuo)題(ti)(ti)時會不知(zhi)所措，從(cong)而無法提高學(xue)習成績.此外，還應掌握(wo)摩(mo)擦起電(dian)(dian)(dian)(dian)(dian)、感(gan)應電(dian)(dian)(dian)(dian)(dian)流、導體和絕緣體等(deng)其他(ta)基(ji)礎知(zhi)識(shi)，理解他(ta)們的(de)(de)含義，利用這些(xie)(xie)知(zhi)識(shi)解決一(yi)些(xie)(xie)電(dian)(dian)(dian)(dian)(dian)學(xue)問題(ti)(ti).

如何打牢基(ji)礎呢？死記硬(ying)背是行(xing)不通的(de).我(wo)們要(yao)對這(zhe)些基(ji)礎知(zhi)識在(zai)理解的(de)基(ji)礎上達(da)到記憶(yi)，并靈活運(yun)用，經常(chang)反(fan)過頭來(lai)回(hui)顧(gu)這(zhe)些基(ji)本知(zhi)識，多(duo)(duo)運(yun)用、多(duo)(duo)記憶(yi)，形(xing)成根(gen)深(shen)蒂固的(de)知(zhi)識網絡.只有打牢了(le)基(ji)礎，才能(neng)進一步提(ti)高電學的(de)學習效率.

二、抓好(hao)重(zhong)難點解析

初中(zhong)(zhong)物(wu)(wu)理(li)的(de)(de)(de)學(xue)(xue)習時間(jian)是(shi)(shi)有(you)限的(de)(de)(de)，學(xue)(xue)生(sheng)學(xue)(xue)習物(wu)(wu)理(li)的(de)(de)(de)精力也(ye)(ye)是(shi)(shi)有(you)限的(de)(de)(de)，而物(wu)(wu)理(li)教(jiao)學(xue)(xue)中(zhong)(zhong)電學(xue)(xue)內(nei)容(rong)是(shi)(shi)博大精深的(de)(de)(de)，所以(yi)我們就要(yao)在有(you)限的(de)(de)(de)時間(jian)和(he)精力下優化物(wu)(wu)理(li)內(nei)容(rong)，抓好物(wu)(wu)理(li)電學(xue)(xue)內(nei)容(rong)的(de)(de)(de)重(zhong)難(nan)點(dian)(dian)(dian)進行有(you)針對(dui)性的(de)(de)(de)學(xue)(xue)習.先要(yao)找出哪些地方(fang)是(shi)(shi)重(zhong)點(dian)(dian)(dian)，哪些是(shi)(shi)難(nan)點(dian)(dian)(dian)，然后對(dui)于(yu)重(zhong)點(dian)(dian)(dian)內(nei)容(rong)，放慢(man)速度，詳細、深入地講(jiang)解，反(fan)復(fu)地訓練，讓(rang)(rang)學(xue)(xue)生(sheng)對(dui)重(zhong)點(dian)(dian)(dian)內(nei)容(rong)有(you)一個更(geng)為(wei)深入的(de)(de)(de)學(xue)(xue)習.對(dui)于(yu)難(nan)點(dian)(dian)(dian)問題，要(yao)分析是(shi)(shi)否也(ye)(ye)作為(wei)電學(xue)(xue)內(nei)容(rong)的(de)(de)(de)重(zhong)點(dian)(dian)(dian)，如(ru)果(guo)作為(wei)重(zhong)點(dian)(dian)(dian)，則需(xu)更(geng)加(jia)注意，通過對(dui)每一個細節的(de)(de)(de)講(jiang)解來使學(xue)(xue)生(sheng)達到(dao)深入；如(ru)果(guo)不作為(wei)重(zhong)點(dian)(dian)(dian)，只需(xu)了解即可，但(dan)也(ye)(ye)需(xu)要(yao)盡量(liang)講(jiang)明(ming)白(bai)，盡量(liang)不讓(rang)(rang)學(xue)(xue)生(sheng)留下疑問.同時，對(dui)于(yu)難(nan)度較大的(de)(de)(de)題目(mu)，教(jiao)師(shi)應采用降低(di)梯度、分設(she)疑點(dian)(dian)(dian)的(de)(de)(de)方(fang)法(fa)，會更(geng)容(rong)易達到(dao)目(mu)的(de)(de)(de).

三、提高分析能力

學(xue)(xue)(xue)習(xi)物(wu)理(li)(li)(li)并(bing)非單純是為(wei)了(le)(le)學(xue)(xue)(xue)習(xi)物(wu)理(li)(li)(li)知識(shi)，更是為(wei)了(le)(le)鍛煉學(xue)(xue)(xue)生(sheng)的(de)(de)(de)分(fen)析(xi)(xi)(xi)(xi)能(neng)力(li)、思維(wei)能(neng)力(li).所(suo)(suo)以(yi)我們在教學(xue)(xue)(xue)物(wu)理(li)(li)(li)電學(xue)(xue)(xue)知識(shi)時，尤其是在教學(xue)(xue)(xue)生(sheng)運用(yong)(yong)電學(xue)(xue)(xue)知識(shi)分(fen)析(xi)(xi)(xi)(xi)和解(jie)(jie)決問題(ti)(ti)的(de)(de)(de)時候，要引導他們分(fen)析(xi)(xi)(xi)(xi)物(wu)理(li)(li)(li)現象和物(wu)理(li)(li)(li)過(guo)程，在分(fen)析(xi)(xi)(xi)(xi)過(guo)程中(zhong)聯系(xi)所(suo)(suo)學(xue)(xue)(xue)知識(shi)，理(li)(li)(li)清思路，循序漸進(jin)，抽絲剝繭，一點一點完成分(fen)析(xi)(xi)(xi)(xi)和解(jie)(jie)題(ti)(ti).對(dui)于概(gai)念(nian)(nian)性問題(ti)(ti)，要認真讀(du)題(ti)(ti)審(shen)(shen)題(ti)(ti)，明確(que)題(ti)(ti)中(zhong)所(suo)(suo)給的(de)(de)(de)條件(jian)和要求(qiu)回答的(de)(de)(de)問題(ti)(ti)，根據(ju)題(ti)(ti)中(zhong)陳述的(de)(de)(de)物(wu)理(li)(li)(li)現象和過(guo)程對(dui)照所(suo)(suo)學(xue)(xue)(xue)知識(shi)選擇解(jie)(jie)題(ti)(ti)所(suo)(suo)要用(yong)(yong)到的(de)(de)(de)概(gai)念(nian)(nian)或(huo)規(gui)律，經過(guo)周密的(de)(de)(de)思考或(huo)分(fen)析(xi)(xi)(xi)(xi)推理(li)(li)(li)，作(zuo)出正確(que)判斷或(huo)回答.對(dui)于計(ji)算題(ti)(ti)，應(ying)在認真審(shen)(shen)題(ti)(ti)的(de)(de)(de)基礎上，根據(ju)題(ti)(ti)目條件(jian)，明確(que)解(jie)(jie)題(ti)(ti)用(yong)(yong)到的(de)(de)(de)概(gai)念(nian)(nian)或(huo)規(gui)律；求(qiu)出正確(que)答案.初(chu)中(zhong)物(wu)理(li)(li)(li)電學(xue)(xue)(xue)計(ji)算題(ti)(ti)是重點，是中(zhong)考必考的(de)(de)(de)內容，而且難度一般(ban)較大（常為(wei)壓軸題(ti)(ti)），可(ke)以(yi)通過(guo)典型(xing)例題(ti)(ti)分(fen)析(xi)(xi)(xi)(xi)，學(xue)(xue)(xue)會(hui)分(fen)析(xi)(xi)(xi)(xi)問題(ti)(ti)的(de)(de)(de)方法和步驟，并(bing)通過(guo)適量練(lian)習(xi)，掌握這(zhe)類計(ji)算題(ti)(ti)的(de)(de)(de)解(jie)(jie)題(ti)(ti)的(de)(de)(de)技(ji)能(neng)、技(ji)巧(qiao)，提(ti)高解(jie)(jie)題(ti)(ti)能(neng)力(li).這(zhe)樣，學(xue)(xue)(xue)生(sheng)在練(lian)習(xi)中(zhong)鍛煉了(le)(le)分(fen)析(xi)(xi)(xi)(xi)、解(jie)(jie)題(ti)(ti)的(de)(de)(de)能(neng)力(li)，又將分(fen)析(xi)(xi)(xi)(xi)、解(jie)(jie)題(ti)(ti)的(de)(de)(de)能(neng)力(li)運用(yong)(yong)與(yu)練(lian)習(xi)中(zhong)，從而取(qu)得(de)良好(hao)的(de)(de)(de)效(xiao)果.

四(si)、重(zhong)視圖形和實(shi)驗

1.重視圖形

圖(tu)(tu)(tu)形(xing)(xing)相對(dui)文字來(lai)(lai)說十(shi)分直(zhi)觀形(xing)(xing)象，由于(yu)物(wu)理具(ju)有(you)抽象性，所以(yi)我們(men)可以(yi)以(yi)圖(tu)(tu)(tu)形(xing)(xing)來(lai)(lai)展示解(jie)題(ti)過程，對(dui)于(yu)復雜難解(jie)的題(ti)目輔之以(yi)圖(tu)(tu)(tu)形(xing)(xing).尤其(qi)(qi)是復雜的電(dian)路(lu)設計，需要(yao)我們(men)運(yun)用圖(tu)(tu)(tu)形(xing)(xing)來(lai)(lai)將(jiang)(jiang)其(qi)(qi)直(zhi)觀化，將(jiang)(jiang)抽象思(si)維(wei)轉變為形(xing)(xing)象思(si)維(wei)，這樣一(yi)來(lai)(lai)，學(xue)生才能更精確(que)地掌握物(wu)理知識.此外，有(you)了圖(tu)(tu)(tu)就能作狀態(tai)分析和(he)動態(tai)分析，明確(que)歐姆定律(lv)應用于(yu)某(mou)一(yi)電(dian)阻還(huan)是整個(ge)電(dian)路(lu).另外還(huan)必(bi)須根據現成的圖(tu)(tu)(tu)形(xing)(xing)學(xue)會識圖(tu)(tu)(tu)，要(yao)學(xue)會在復雜的圖(tu)(tu)(tu)形(xing)(xing)中看出基本圖(tu)(tu)(tu)形(xing)(xing).

2.重視實驗

篇9

關鍵詞(ci)：初中物理；電學；控(kong)制(zhi)變量(liang)法；探究(jiu)

一、探究(jiu)物理規律中控(kong)制(zhi)變量法的應用

歐姆定(ding)(ding)律是(shi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)學(xue)的(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)基礎(chu)和重點(dian)，處(chu)于(yu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)學(xue)的(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)核心位置(zhi)。學(xue)生(sheng)們通過之(zhi)前的(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)學(xue)習掌(zhang)握(wo)了(le)(le)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)學(xue)的(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)3個基本概念：電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)、電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)(ya)(ya)(ya)(ya)(ya)(ya)(ya)、電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)(zu)(zu)(zu)。它們之(zhi)間有(you)怎樣(yang)的(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)關(guan)系呢？根(gen)據新課程標準的(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)要(yao)求，教(jiao)(jiao)材(cai)安(an)排了(le)(le)一個比較完整(zheng)的(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)探(tan)究(jiu)活動，涵(han)蓋了(le)(le)探(tan)究(jiu)的(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)3個要(yao)素。其中(zhong)重點(dian)是(shi)如何運用(yong)(yong)控(kong)制(zhi)變(bian)(bian)(bian)(bian)(bian)(bian)量法(fa)(fa)(fa)來設計整(zheng)個實(shi)驗(yan)，明(ming)確用(yong)(yong)什(shen)么(me)方(fang)法(fa)(fa)(fa)保證什(shen)么(me)物理(li)量不變(bian)(bian)(bian)(bian)(bian)(bian)，用(yong)(yong)什(shen)么(me)方(fang)法(fa)(fa)(fa)改(gai)(gai)變(bian)(bian)(bian)(bian)(bian)(bian)什(shen)么(me)物理(li)量。1.控(kong)制(zhi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)(zu)(zu)(zu)R不變(bian)(bian)(bian)(bian)(bian)(bian)，改(gai)(gai)變(bian)(bian)(bian)(bian)(bian)(bian)導體(ti)兩(liang)(liang)(liang)端(duan)(duan)(duan)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)(ya)(ya)(ya)(ya)(ya)(ya)(ya)U，探(tan)究(jiu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)I與(yu)(yu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)(ya)(ya)(ya)(ya)(ya)(ya)(ya)U之(zhi)間的(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)關(guan)系。（1）固定(ding)(ding)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)(zu)(zu)(zu)值(zhi)(zhi)(zhi)，可(ke)保證定(ding)(ding)值(zhi)(zhi)(zhi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)(zu)(zu)(zu)R的(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)阻(zu)(zu)(zu)(zu)(zu)(zu)(zu)值(zhi)(zhi)(zhi)不變(bian)(bian)(bian)(bian)(bian)(bian)。（2）影(ying)響導體(ti)兩(liang)(liang)(liang)端(duan)(duan)(duan)的(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)(ya)(ya)(ya)(ya)(ya)(ya)(ya)值(zhi)(zhi)(zhi)的(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)改(gai)(gai)變(bian)(bian)(bian)(bian)(bian)(bian)，可(ke)用(yong)(yong)兩(liang)(liang)(liang)種辦法(fa)(fa)(fa)：1.改(gai)(gai)變(bian)(bian)(bian)(bian)(bian)(bian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)兩(liang)(liang)(liang)端(duan)(duan)(duan)的(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)(ya)(ya)(ya)(ya)(ya)(ya)(ya)，即可(ke)改(gai)(gai)變(bian)(bian)(bian)(bian)(bian)(bian)導體(ti)兩(liang)(liang)(liang)端(duan)(duan)(duan)的(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)(ya)(ya)(ya)(ya)(ya)(ya)(ya)U。用(yong)(yong)這(zhe)個電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)路(lu)，學(xue)生(sheng)能夠較為輕松地運用(yong)(yong)控(kong)制(zhi)變(bian)(bian)(bian)(bian)(bian)(bian)量的(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)方(fang)法(fa)(fa)(fa)研究(jiu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)與(yu)(yu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)(ya)(ya)(ya)(ya)(ya)(ya)(ya)的(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)關(guan)系，易(yi)于(yu)學(xue)生(sheng)理(li)解和掌(zhang)握(wo)。2.通過調節滑(hua)動變(bian)(bian)(bian)(bian)(bian)(bian)阻(zu)(zu)(zu)(zu)(zu)(zu)(zu)器，改(gai)(gai)變(bian)(bian)(bian)(bian)(bian)(bian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)(zu)(zu)(zu)R兩(liang)(liang)(liang)端(duan)(duan)(duan)的(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)(ya)(ya)(ya)(ya)(ya)(ya)(ya)。要(yao)使(shi)(shi)學(xue)生(sheng)明(ming)確研究(jiu)對象(xiang)是(shi)定(ding)(ding)值(zhi)(zhi)(zhi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)(zu)(zu)(zu)這(zhe)部分電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)路(lu)，滑(hua)動變(bian)(bian)(bian)(bian)(bian)(bian)阻(zu)(zu)(zu)(zu)(zu)(zu)(zu)器的(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)作用(yong)(yong)是(shi)為了(le)(le)使(shi)(shi)定(ding)(ding)值(zhi)(zhi)(zhi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)(zu)(zu)(zu)兩(liang)(liang)(liang)端(duan)(duan)(duan)的(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)(ya)(ya)(ya)(ya)(ya)(ya)(ya)發(fa)生(sheng)改(gai)(gai)變(bian)(bian)(bian)(bian)(bian)(bian)。2.保持(chi)導體(ti)兩(liang)(liang)(liang)端(duan)(duan)(duan)的(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)(ya)(ya)(ya)(ya)(ya)(ya)(ya)U不變(bian)(bian)(bian)(bian)(bian)(bian)，改(gai)(gai)變(bian)(bian)(bian)(bian)(bian)(bian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)(zu)(zu)(zu)R，研究(jiu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)與(yu)(yu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)(zu)(zu)(zu)的(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)關(guan)系。（1）用(yong)(yong)不同(tong)(tong)的(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)定(ding)(ding)值(zhi)(zhi)(zhi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)(zu)(zu)(zu)可(ke)改(gai)(gai)變(bian)(bian)(bian)(bian)(bian)(bian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)(zu)(zu)(zu)R的(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)值(zhi)(zhi)(zhi)。（2）變(bian)(bian)(bian)(bian)(bian)(bian)動電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)(zu)(zu)(zu)R的(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)同(tong)(tong)時必須保證導體(ti)兩(liang)(liang)(liang)端(duan)(duan)(duan)的(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)(ya)(ya)(ya)(ya)(ya)(ya)(ya)不改(gai)(gai)變(bian)(bian)(bian)(bian)(bian)(bian)，可(ke)以采用(yong)(yong)以下兩(liang)(liang)(liang)種方(fang)法(fa)(fa)(fa)：使(shi)(shi)用(yong)(yong)同(tong)(tong)一個電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)，即可(ke)保證導體(ti)兩(liang)(liang)(liang)端(duan)(duan)(duan)的(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)(ya)(ya)(ya)(ya)(ya)(ya)(ya)不變(bian)(bian)(bian)(bian)(bian)(bian)，更換不同(tong)(tong)的(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)(zu)(zu)(zu)，可(ke)直接(jie)得出(chu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)與(yu)(yu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)(zu)(zu)(zu)的(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)關(guan)系，降低了(le)(le)探(tan)究(jiu)的(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)難度(du)。但如果實(shi)驗(yan)中(zhong)使(shi)(shi)用(yong)(yong)的(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)是(shi)干(gan)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池，電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池有(you)內(nei)阻(zu)(zu)(zu)(zu)(zu)(zu)(zu)，外接(jie)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)(zu)(zu)(zu)R變(bian)(bian)(bian)(bian)(bian)(bian)化時，電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)(zu)(zu)(zu)R兩(liang)(liang)(liang)端(duan)(duan)(duan)的(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)(ya)(ya)(ya)(ya)(ya)(ya)(ya)也會隨之(zhi)變(bian)(bian)(bian)(bian)(bian)(bian)化，給(gei)實(shi)驗(yan)帶來誤差。換用(yong)(yong)阻(zu)(zu)(zu)(zu)(zu)(zu)(zu)值(zhi)(zhi)(zhi)不同(tong)(tong)的(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)(zu)(zu)(zu)R時，若(ruo)滑(hua)動變(bian)(bian)(bian)(bian)(bian)(bian)阻(zu)(zu)(zu)(zu)(zu)(zu)(zu)器的(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)滑(hua)片不動，定(ding)(ding)值(zhi)(zhi)(zhi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)(zu)(zu)(zu)兩(liang)(liang)(liang)端(duan)(duan)(duan)的(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)(ya)(ya)(ya)(ya)(ya)(ya)(ya)會發(fa)生(sheng)變(bian)(bian)(bian)(bian)(bian)(bian)化。電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)(ya)(ya)(ya)(ya)(ya)(ya)(ya)、電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)(zu)(zu)(zu)都改(gai)(gai)變(bian)(bian)(bian)(bian)(bian)(bian)，就(jiu)不能確定(ding)(ding)究(jiu)竟是(shi)什(shen)么(me)因素影(ying)響了(le)(le)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)。這(zhe)一點(dian)學(xue)生(sheng)在實(shi)驗(yan)中(zhong)容(rong)易(yi)忽(hu)視，教(jiao)(jiao)師要(yao)注意引導學(xue)生(sheng)觀(guan)察電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)(ya)(ya)(ya)(ya)(ya)(ya)(ya)表，使(shi)(shi)其示數(shu)保持(chi)不變(bian)(bian)(bian)(bian)(bian)(bian)。經(jing)過以上兩(liang)(liang)(liang)個環節的(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)探(tan)究(jiu)，學(xue)生(sheng)得出(chu)導體(ti)中(zhong)的(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)與(yu)(yu)導體(ti)兩(liang)(liang)(liang)端(duan)(duan)(duan)的(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)(ya)(ya)(ya)(ya)(ya)(ya)(ya)和導體(ti)的(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)(zu)(zu)(zu)的(de)(de)(de)(de)(de)(de)(de)(de)(de)(de)關(guan)系，便水到渠成了(le)(le)。

二、電學(xue)習題中控(kong)制變量法(fa)的運(yun)用

1.在比較物理量的大小時用控(kong)制變(bian)量的思路

例1：已(yi)知甲(jia)導體(ti)的(de)(de)電(dian)(dian)(dian)(dian)(dian)阻比乙(yi)導體(ti)的(de)(de)電(dian)(dian)(dian)(dian)(dian)阻大，把(ba)它們(men)并聯在(zai)電(dian)(dian)(dian)(dian)(dian)路(lu)中，比較甲(jia)的(de)(de)電(dian)(dian)(dian)(dian)(dian)功率(lv)和(he)乙(yi)的(de)(de)電(dian)(dian)(dian)(dian)(dian)功率(lv)。簡析：求解電(dian)(dian)(dian)(dian)(dian)功率(lv)的(de)(de)公式(shi)比較多：P=UI，P=U2/R，P=I2R，學(xue)生分(fen)析起(qi)(qi)來常常感到無從下手。電(dian)(dian)(dian)(dian)(dian)功率(lv)與(yu)兩個(ge)(ge)因素(su)有關(guan)。可(ke)(ke)引導學(xue)生用控制變(bian)量法的(de)(de)思(si)路(lu)解決這類問題。關(guan)鍵在(zai)于根(gen)據題目意(yi)思(si)找(zhao)到起(qi)(qi)相(xiang)同(tong)作(zuo)用的(de)(de)因素(su)，只讓一個(ge)(ge)因素(su)發生變(bian)化(hua)，再分(fen)析電(dian)(dian)(dian)(dian)(dian)功率(lv)與(yu)另一個(ge)(ge)變(bian)量之間的(de)(de)關(guan)系。具體(ti)分(fen)析如下：并聯時，各(ge)支路(lu)兩端電(dian)(dian)(dian)(dian)(dian)壓相(xiang)等(deng)，所以我們(men)可(ke)(ke)以選擇P=U2/R或P=UI。已(yi)知R甲(jia)>R乙(yi)，可(ke)(ke)根(gen)據P=U2R直接得出P甲(jia)R乙(yi)，由并聯電(dian)(dian)(dian)(dian)(dian)路(lu)可(ke)(ke)知I甲(jia)

2.在突破動態(tai)電路(lu)的難點中(zhong)運(yun)用控制變量(liang)的思(si)路(lu)

例2：如圖3所示電(dian)路，試分(fen)析當(dang)滑動(dong)變(bian)阻器的滑片向左移動(dong)時，電(dian)流表(biao)和電(dian)壓表(biao)的示數如何變(bian)化？

簡析：引(yin)導(dao)學生(sheng)從U=IR入手(shou)，電(dian)(dian)(dian)(dian)壓與電(dian)(dian)(dian)(dian)流(liu)(liu)和(he)電(dian)(dian)(dian)(dian)阻(zu)兩(liang)個(ge)(ge)因(yin)素有(you)關，當I、R都發生(sheng)變(bian)(bian)(bian)化(hua)(hua)時（R變(bian)(bian)(bian)小(xiao)，I變(bian)(bian)(bian)大(da)(da)），很難(nan)判(pan)定(ding)U如何變(bian)(bian)(bian)化(hua)(hua)。此時最好運用(yong)控制變(bian)(bian)(bian)量的(de)(de)(de)(de)思路(lu)，保證I、R其中(zhong)(zhong)一個(ge)(ge)因(yin)素不(bu)變(bian)(bian)(bian)，只(zhi)改(gai)變(bian)(bian)(bian)另一個(ge)(ge)因(yin)素。電(dian)(dian)(dian)(dian)路(lu)中(zhong)(zhong)的(de)(de)(de)(de)電(dian)(dian)(dian)(dian)流(liu)(liu)I肯定(ding)要發生(sheng)改(gai)變(bian)(bian)(bian)，所(suo)以(yi)從定(ding)值電(dian)(dian)(dian)(dian)阻(zu)R入手(shou)。電(dian)(dian)(dian)(dian)路(lu)中(zhong)(zhong)的(de)(de)(de)(de)電(dian)(dian)(dian)(dian)流(liu)(liu)I變(bian)(bian)(bian)大(da)(da)，R不(bu)變(bian)(bian)(bian)，根(gen)據歐姆定(ding)律可(ke)知，R兩(liang)端的(de)(de)(de)(de)電(dian)(dian)(dian)(dian)壓UR變(bian)(bian)(bian)大(da)(da)。電(dian)(dian)(dian)(dian)源電(dian)(dian)(dian)(dian)壓不(bu)變(bian)(bian)(bian)，UR變(bian)(bian)(bian)大(da)(da)，則UC變(bian)(bian)(bian)小(xiao)。此電(dian)(dian)(dian)(dian)路(lu)是(shi)電(dian)(dian)(dian)(dian)學中(zhong)(zhong)的(de)(de)(de)(de)一個(ge)(ge)典型的(de)(de)(de)(de)電(dian)(dian)(dian)(dian)路(lu)，很多中(zhong)(zhong)考(kao)題都是(shi)由此題衍(yan)生(sheng)出來(lai)的(de)(de)(de)(de)。在分(fen)析過程中(zhong)(zhong)，學生(sheng)普遍感(gan)到困難(nan)，準確(que)率低。學生(sheng)對滑(hua)片向左(zuo)移動時，滑(hua)動變(bian)(bian)(bian)阻(zu)器的(de)(de)(de)(de)電(dian)(dian)(dian)(dian)阻(zu)Rc的(de)(de)(de)(de)變(bian)(bian)(bian)化(hua)(hua)和(he)電(dian)(dian)(dian)(dian)路(lu)中(zhong)(zhong)電(dian)(dian)(dian)(dian)流(liu)(liu)I的(de)(de)(de)(de)變(bian)(bian)(bian)化(hua)(hua)比較容易判(pan)斷。但對于UR、UC的(de)(de)(de)(de)變(bian)(bian)(bian)化(hua)(hua)就(jiu)(jiu)感(gan)到無從下手(shou)。學生(sheng)明白了這(zhe)樣分(fen)析的(de)(de)(de)(de)原因(yin)，就(jiu)(jiu)會(hui)正確(que)地運用(yong)控制變(bian)(bian)(bian)量法來(lai)突破難(nan)點了。

三(san)、用控制變量(liang)法來學習電阻

學(xue)(xue)(xue)生(sheng)(sheng)通(tong)過之前的(de)學(xue)(xue)(xue)習掌握了(le)電(dian)(dian)路的(de)兩個基本部(bu)分：電(dian)(dian)流(liu)及電(dian)(dian)壓(ya)(ya)；緊(jin)接著學(xue)(xue)(xue)習電(dian)(dian)阻，學(xue)(xue)(xue)生(sheng)(sheng)的(de)壓(ya)(ya)力不會很(hen)大，但這(zhe)時學(xue)(xue)(xue)生(sheng)(sheng)對科學(xue)(xue)(xue)探究物理的(de)方法還沒(mei)什(shen)么概念(nian)。這(zhe)時教師(shi)會根據課(ke)程的(de)要求(qiu)授完這(zhe)節課(ke)，然(ran)后引入“控制變(bian)量法”安排一節課(ke)，有針對性(xing)地講解一些典型例(li)題(ti)。

例3：在(zai)探究“導(dao)體電阻大(da)小(xiao)與哪些因素有關”的實驗時(shi)，將(jiang)一根粗(cu)細均勻(yun)的導(dao)體截成兩段(duan)后分別接入如圖1所示的電路中(zhong)，這(zhe)是用來(lai)探究（ ）。

A、導(dao)體電阻與橫截(jie)面積的關系(xi)；

B、導體電(dian)阻與(yu)材料的關系；

C、導體電阻與長度(du)的(de)關系；

D、導體電阻與溫度的關系。

解析：從題中所(suo)給(gei)的條件看，兩段(duan)導體(ti)是同一(yi)段(duan)導體(ti)按不同的長(chang)度(du)(du)(du)截(jie)取的，即它們的材料(liao)、橫截(jie)面積及溫度(du)(du)(du)是相同的，但是長(chang)度(du)(du)(du)不同。這樣學生就很容易得出答案(an)C。

但學生要(yao)掌(zhang)握的是(shi)：本題由教材上的演示(shi)實驗演化(hua)而來，這是(shi)中考試題常出現的命題來源(yuan)，更重要(yao)的是(shi)，本題中涉及了對控制變量(liang)法的理解(jie)和應用。

四、在(zai)學習(xi)電(dian)學實驗中利用控(kong)制變量法(fa)

在(zai)總結“電磁鐵(tie)磁性的強弱與什么(me)因素有關”的實驗(yan)時，我們會(hui)用到如下圖(tu)所示的例題(ti)：

篇10

《義(yi)務教(jiao)(jiao)育物理(li)課程標準》中(zhong)(zhong)明確(que)指出初中(zhong)(zhong)物理(li)是(shi)一門注(zhu)(zhu)重實驗的(de)自然科(ke)(ke)(ke)學(xue)基(ji)礎課程。此階段的(de)物理(li)課程應注(zhu)(zhu)意(yi)讓學(xue)生(sheng)經(jing)歷實驗探(tan)究過(guo)程，學(xue)習(xi)科(ke)(ke)(ke)學(xue)知識和科(ke)(ke)(ke)學(xue)探(tan)究方法，提高(gao)分(fen)析問題(ti)及(ji)解決問題(ti)的(de)能力(li)。新課程理(li)念要(yao)求教(jiao)(jiao)師在物理(li)實驗教(jiao)(jiao)學(xue)中(zhong)(zhong)，注(zhu)(zhu)重形(xing)成性評價與終結性評相結合，注(zhu)(zhu)重采用探(tan)究式的(de)教(jiao)(jiao)學(xue)方法讓學(xue)生(sheng)經(jing)歷探(tan)究過(guo)程，學(xue)習(xi)科(ke)(ke)(ke)學(xue)方法，培(pei)養其(qi)創(chuang)新精神(shen)和實驗能力(li)。

筆者參(can)加了貴州(zhou)省(sheng)中(zhong)學(xue)(xue)教師繼續教育培(pei)(pei)訓(xun)，對新(xin)課改(gai)有了清晰(xi)的(de)認(ren)識(shi)：新(xin)課改(gai)中(zhong)一定要(yao)重(zhong)視實(shi)(shi)驗(yan)教學(xue)(xue)，加強實(shi)(shi)驗(yan)教學(xue)(xue)不僅僅是(shi)要(yao)培(pei)(pei)養(yang)學(xue)(xue)生(sheng)的(de)動手能力，更重(zhong)要(yao)的(de)是(shi)培(pei)(pei)養(yang)學(xue)(xue)生(sheng)科(ke)(ke)學(xue)(xue)研究問題方(fang)法(fa)、提高學(xue)(xue)生(sheng)學(xue)(xue)習物理的(de)興趣、培(pei)(pei)養(yang)學(xue)(xue)生(sheng)多方(fang)面(mian)的(de)科(ke)(ke)學(xue)(xue)素(su)質(zhi)。通過實(shi)(shi)驗(yan)教學(xue)(xue)，使學(xue)(xue)生(sheng)在學(xue)(xue)到知(zhi)識(shi)和技能的(de)同時(shi)，經歷科(ke)(ke)學(xue)(xue)探究的(de)過程(cheng)，尊重(zhong)事實(shi)(shi)的(de)科(ke)(ke)學(xue)(xue)精神和情感教育滲透其中(zhong)。

筆者所(suo)教的學校是一所(suo)遠離城市的農村初級中學，雖然學校建有(you)物理實(shi)(shi)驗(yan)室，但是有(you)時(shi)實(shi)(shi)驗(yan)器材，工具有(you)限，只(zhi)有(you)因(yin)材施(shi)教，因(yin)地制宜地去開(kai)展物理實(shi)(shi)驗(yan)教學。

將所任教班級的全體學(xue)生(sheng)(sheng)編為A、B、C、D四個小組，教師親自帶領全體學(xue)生(sheng)(sheng)去物(wu)理實(shi)驗室(shi)去做(zuo)實(shi)驗。嚴(yan)格(ge)要(yao)求學(xue)生(sheng)(sheng)按(an)照實(shi)驗步驟去做(zuo)，并且提醒全體學(xue)生(sheng)(sheng)注(zhu)意安(an)(an)全。比如(ru)，在做(zuo)電學(xue)的實(shi)驗時，教育學(xue)生(sheng)(sheng)安(an)(an)全用(yong)電，避免觸(chu)電事故發生(sheng)(sheng)。

第一，對做實驗(yan)過(guo)程中，認(ren)真(zhen)操(cao)作，迅速得出結(jie)論的同(tong)學(xue)當(dang)面給予表揚，激勵(li)其他學(xue)生向認(ren)真(zhen)做實驗(yan)的同(tong)學(xue)學(xue)習(xi)。

第二，每(mei)次實驗操(cao)作之(zhi)后，教師(shi)組(zu)織全(quan)(quan)體(ti)(ti)學(xue)(xue)生(sheng)(sheng)(sheng)討論、交流，小組(zu)合(he)作開(kai)展(zhan)(zhan)活動，培(pei)養(yang)(yang)學(xue)(xue)生(sheng)(sheng)(sheng)之(zhi)間的團隊精神。從學(xue)(xue)習(xi)的角(jiao)度來說，每(mei)位成員在學(xue)(xue)習(xi)上的想法(fa)都為(wei)整個(ge)小組(zu)所共(gong)享，個(ge)人(ren)獲(huo)得的知識(shi)是(shi)集體(ti)(ti)智慧的結(jie)晶，這(zhe)也是(shi)合(he)作精神的體(ti)(ti)現。這(zhe)也是(shi)符合(he)新課(ke)程(cheng)的基本(ben)理念：面向全(quan)(quan)體(ti)(ti)學(xue)(xue)生(sheng)(sheng)(sheng)，提高學(xue)(xue)生(sheng)(sheng)(sheng)科學(xue)(xue)素(su)養(yang)(yang)。以(yi)生(sheng)(sheng)(sheng)為(wei)本(ben)，為(wei)每(mei)個(ge)學(xue)(xue)生(sheng)(sheng)(sheng)的學(xue)(xue)習(xi)與(yu)發展(zhan)(zhan)，提供機會，使每(mei)個(ge)學(xue)(xue)生(sheng)(sheng)(sheng)學(xue)(xue)習(xi)物(wu)理的潛能都得到發展(zhan)(zhan)。

第(di)三，筆者(zhe)針對(dui)目前農村(cun)初中(zhong)物理教學(xue)(xue)(xue)的現狀，根據實(shi)(shi)(shi)(shi)(shi)(shi)驗(yan)(yan)(yan)(yan)(yan)內容(rong)，教學(xue)(xue)(xue)目標，實(shi)(shi)(shi)(shi)(shi)(shi)驗(yan)(yan)(yan)(yan)(yan)條(tiao)件(jian)等，設(she)計成(cheng)演(yan)(yan)示(shi)實(shi)(shi)(shi)(shi)(shi)(shi)驗(yan)(yan)(yan)(yan)(yan)或(huo)學(xue)(xue)(xue)生(sheng)(sheng)實(shi)(shi)(shi)(shi)(shi)(shi)驗(yan)(yan)(yan)(yan)(yan)，適當增設(she)一些(xie)與中(zhong)考(kao)相關的學(xue)(xue)(xue)生(sheng)(sheng)實(shi)(shi)(shi)(shi)(shi)(shi)驗(yan)(yan)(yan)(yan)(yan)題(ti)，多(duo)抽空閑時(shi)間帶領全(quan)班學(xue)(xue)(xue)生(sheng)(sheng)親(qin)自動手去實(shi)(shi)(shi)(shi)(shi)(shi)驗(yan)(yan)(yan)(yan)(yan)室操作。無論是(shi)(shi)演(yan)(yan)示(shi)實(shi)(shi)(shi)(shi)(shi)(shi)驗(yan)(yan)(yan)(yan)(yan)還是(shi)(shi)學(xue)(xue)(xue)生(sheng)(sheng)實(shi)(shi)(shi)(shi)(shi)(shi)驗(yan)(yan)(yan)(yan)(yan)，都盡量讓全(quan)體學(xue)(xue)(xue)生(sheng)(sheng)明確實(shi)(shi)(shi)(shi)(shi)(shi)驗(yan)(yan)(yan)(yan)(yan)目的，理解實(shi)(shi)(shi)(shi)(shi)(shi)驗(yan)(yan)(yan)(yan)(yan)原理。如果是(shi)(shi)做演(yan)(yan)示(shi)實(shi)(shi)(shi)(shi)(shi)(shi)驗(yan)(yan)(yan)(yan)(yan)，由于是(shi)(shi)教師操作，學(xue)(xue)(xue)生(sheng)(sheng)的主要任務是(shi)(shi)觀察和思考(kao)，因此，教師應注意指導(dao)學(xue)(xue)(xue)生(sheng)(sheng)觀察實(shi)(shi)(shi)(shi)(shi)(shi)驗(yan)(yan)(yan)(yan)(yan)現象，啟發學(xue)(xue)(xue)生(sheng)(sheng)對(dui)實(shi)(shi)(shi)(shi)(shi)(shi)驗(yan)(yan)(yan)(yan)(yan)現象所(suo)說(shuo)明的問題(ti)進行積極思考(kao)和交流。

目前，貴州省的初(chu)級中學物理使用的教(jiao)材是上(shang)海科學技(ji)術出版社(she)出版的書(shu)。該(gai)書(shu)內容(rong)豐富，物理實驗偏(pian)多(duo)，教(jiao)師要參(can)照教(jiao)學大綱，考試(shi)大綱，抓住(zhu)重點和難點。

例(li)如：（1）九(jiu)年級(ji)物(wu)理電學中的一個實(shi)驗：電阻(zu)的并聯：

參照(zhao)探究(jiu)串聯電阻的思路(lu)的步驟，先設計實(shi)驗探究(jiu)：幾(ji)個電阻并聯后的總電阻與各(ge)分(fen)(fen)電阻相(xiang)比較(jiao)，是大(da)了還是小了？然后再根據歐姆(mu)定律(lv)，從理論上推導出總電阻和分(fen)(fen)電阻大(da)小之間的定量關(guan)系，通過老師指導學生(sheng)做實(shi)驗，利用歐姆(mu)定律(lv)從理論上推導出結論。

兩個(ge)并(bing)聯的(de)電阻(zu)(zu)的(de)總電阻(zu)(zu)的(de)倒(dao)數(shu)，等于兩分電阻(zu)(zu)的(de)倒(dao)數(shu)之和。

（2）八年級(ji)物理力學中的(de)一個(ge)實驗：探究物重與物體質量的(de)關系：

實驗器材：彈簧測(ce)力計、質量(liang)庫50g的(de)鉤碼6只。

實驗(yan)操作：分別把1只(zhi)(zhi)、2只(zhi)(zhi)、3只(zhi)(zhi)……6只(zhi)(zhi)鉤碼掛在彈簧力(li)計上，記下彈簧測力(li)計每一(yi)次的示數。

物重所(suo)愛重力(li)大小跟它(ta)的(de)(de)質量(liang)(liang)正比，其比值(zhi)是定值(zhi)，約(yue)等于(yu)9.8N/kg。若用字母g表示一(yi)個物體的(de)(de)物重跟這個物體的(de)(de)質量(liang)(liang)之比。

在(zai)農村中學(xue)(xue)(xue)(xue)現有(you)的(de)(de)(de)(de)條(tiao)件下，建議各位老師對(dui)學(xue)(xue)(xue)(xue)生(sheng)加(jia)(jia)(jia)強(qiang)實驗教學(xue)(xue)(xue)(xue)，新課標(biao)“重(zhong)過程(cheng)、重(zhong)方(fang)法”，就是(shi)要學(xue)(xue)(xue)(xue)生(sheng)親(qin)(qin)身經歷獲得(de)(de)知識的(de)(de)(de)(de)過程(cheng)，加(jia)(jia)(jia)深對(dui)物(wu)(wu)理(li)(li)(li)理(li)(li)(li)論知識的(de)(de)(de)(de)理(li)(li)(li)解，領悟科(ke)學(xue)(xue)(xue)(xue)探(tan)究的(de)(de)(de)(de)方(fang)法，體驗探(tan)究過程(cheng)的(de)(de)(de)(de)樂趣，分享探(tan)究成功的(de)(de)(de)(de)喜悅，激發學(xue)(xue)(xue)(xue)習物(wu)(wu)理(li)(li)(li)的(de)(de)(de)(de)興趣。初中物(wu)(wu)理(li)(li)(li)教材中的(de)(de)(de)(de)物(wu)(wu)理(li)(li)(li)公(gong)式和物(wu)(wu)理(li)(li)(li)規律(lv)性，都是(shi)通過科(ke)學(xue)(xue)(xue)(xue)探(tan)究得(de)(de)出的(de)(de)(de)(de)。讓學(xue)(xue)(xue)(xue)生(sheng)親(qin)(qin)自動手(shou)、親(qin)(qin)身體驗物(wu)(wu)理(li)(li)(li)規律(lv)獲得(de)(de)的(de)(de)(de)(de)過程(cheng)，能使(shi)學(xue)(xue)(xue)(xue)生(sheng)記憶深刻(ke)。即便(bian)在(zai)運(yun)用時偶然忘記了公(gong)式，多數情(qing)況下當他(ta)們加(jia)(jia)(jia)快探(tan)究過程(cheng)時會重(zhong)新記起來。因此(ci)加(jia)(jia)(jia)強(qiang)探(tan)究實驗教學(xue)(xue)(xue)(xue)，對(dui)學(xue)(xue)(xue)(xue)生(sheng)解答包(bao)括綜合計算題在(zai)內(nei)的(de)(de)(de)(de)各種題型都有(you)幫助，同時也能提高學(xue)(xue)(xue)(xue)生(sheng)的(de)(de)(de)(de)自學(xue)(xue)(xue)(xue)能力。

指導(dao)學(xue)生(sheng)(sheng)做(zuo)物(wu)(wu)理(li)實驗有利于(yu)培養學(xue)生(sheng)(sheng)的(de)(de)物(wu)(wu)理(li)思(si)(si)(si)(si)維(wei)方法(fa)。物(wu)(wu)理(li)思(si)(si)(si)(si)維(wei)方法(fa)包(bao)括(kuo)分析(xi)、綜(zong)合、比(bi)較(jiao)、抽(chou)象(xiang)、概括(kuo)、歸(gui)納等。解決(jue)物(wu)(wu)理(li)計算問題時，分析(xi)、綜(zong)合、比(bi)較(jiao)應(ying)用得更為普(pu)遍，順藤摸瓜法(fa)和發(fa)散思(si)(si)(si)(si)維(wei)法(fa)，它是(shi)從已知條件推論其結果的(de)(de)方法(fa)。發(fa)散思(si)(si)(si)(si)維(wei)法(fa)是(shi)從某條物(wu)(wu)理(li)規律出發(fa)，找(zhao)出規律　的(de)(de)多種(zhong)表(biao)述，是(shi)形成熟練的(de)(de)技(ji)能技(ji)巧的(de)(de)重(zhong)要方法(fa)。教學(xue)時要注意對學(xue)生(sheng)(sheng)思(si)(si)(si)(si)維(wei)方法(fa)的(de)(de)培養，達到勤(qin)于(yu)思(si)(si)(si)(si)考(kao)(kao)、善(shan)于(yu)思(si)(si)(si)(si)考(kao)(kao)的(de)(de)培養目標。

中學物理(li)(li)教(jiao)(jiao)(jiao)師應(ying)通(tong)過各種途(tu)徑開發實(shi)(shi)驗(yan)(yan)(yan)課程資源。教(jiao)(jiao)(jiao)師可(ke)用(yong)已有的(de)(de)實(shi)(shi)驗(yan)(yan)(yan)器(qi)材進行實(shi)(shi)驗(yan)(yan)(yan)教(jiao)(jiao)(jiao)學，也(ye)可(ke)用(yong)效(xiao)果(guo)更(geng)明顯(xian)、實(shi)(shi)驗(yan)(yan)(yan)誤(wu)差(cha)更(geng)小(xiao)的(de)(de)新(xin)實(shi)(shi)驗(yan)(yan)(yan)器(qi)材是進行實(shi)(shi)驗(yan)(yan)(yan)教(jiao)(jiao)(jiao)學，還可(ke)讓(rang)學生(sheng)了解一些新(xin)的(de)(de)實(shi)(shi)驗(yan)(yan)(yan)技術(shu)。同時，應(ying)大力提(ti)倡用(yong)身邊的(de)(de)實(shi)(shi)驗(yan)(yan)(yan)，這樣既可(ke)以拉近物理(li)(li)學與(yu)生(sheng)活的(de)(de)距離，讓(rang)學生(sheng)深切地感覺到科學的(de)(de)真實(shi)(shi)性，又補(bu)充實(shi)(shi)驗(yan)(yan)(yan)課程資源，有利于增強學生(sheng)的(de)(de)創新(xin)意識。

參考文獻：

[1]《義務教(jiao)育物理課程標準實驗教(jiao)科(ke)書——物理》上海，上海科(ke)學技術出版(ban)社，2002年(nian)8月第1版(ban).