第2课时电路闭合电路欧姆定律【考纲解读】1.熟练掌握串、并联电路的特点，并能分析、计算.2.理解闭合电路欧姆定律，并能进行电路的动态分析和计算．【知识要点】1．闭合电路欧姆定律的公式2．路端电压U与电流I的关系(1)关系式：U＝.(2)U－I图象如图1所示．①当电路断路即I＝0时，纵坐标的截距为②当外电路短路即U＝0时，横坐标的截距为③图线的斜率的绝对值为电源的内阻．3．电源的总功率(1)任意电路：P总＝＝＋IU内＝P出＋P内．(2)纯电阻电路：P总＝＝.4．电源内部消耗的功率：P内＝＝＝P总－P出．5．电源的输出功率(1)任意电路：P出＝＝IE－I2r＝P总－P内．(2)纯电阻电路：P出＝I2R＝＝.6．电源的效率(1)任意电路：η＝×100%＝×100%.(2)纯电阻电路：η＝×100%＝×100%【典型例题】例1.如图所示，E为内阻不能忽略的电池，R1、R2、R3为定值电阻，S0、S为开关，INCLUDEPICTURE"E:\\2015\\Word\\物理\\一轮物理\\圈V.TIF"\*MERGEFORMATINCLUDEPICTURE"E:\\2015\\Word\\物理\\一轮物理\\圈V.TIF"\*MERGEFORMATINCLUDEPICTURE"E:\\2015\\Word\\物理\\一轮物理\\圈V.TIF"\*MERGEFORMATINCLUDEPICTURE"E:\\鹿晴晴\\2015\\一轮\\Word\\一轮\\物理\\圈V.TIF"\*MERGEFORMATINETINCLUDEPICTURE"D:\\杨爱珍\\江苏\\word\\圈V.TIF"\*MERGEFORMATINET与INCLUDEPICTURE"E:\\2015\\Word\\物理\\一轮物理\\圈A.TIF"\*MERGEFORMATINCLUDEPICTURE"E:\\2015\\Word\\物理\\一轮物理\\圈A.TIF"\*MERGEFORMATINCLUDEPICTURE"E:\\2015\\Word\\物理\\一轮物理\\圈A.TIF"\*MERGEFORMATINCLUDEPICTURE"E:\\鹿晴晴\\2015\\一轮\\Word\\一轮\\物理\\圈A.TIF"\*MERGEFORMATINETINCLUDEPICTURE"D:\\杨爱珍\\江苏\\word\\圈A.TIF"\*MERGEFORMATINET分别为电压表与电流表．初始时S0与S均闭合，现将S断开，则()1A.INCLUDEPICTURE"E:\\2015\\Word\\物理\\一轮物理\\圈V.TIF"\*MERGEFORMATINCLUDEPICTURE"E:\\2015\\Word\\物理\\一轮物理\\圈V.TIF"\*MERGEFORMATINCLUDEPICTURE"E:\\2015\\Word\\物理\\一轮物理\\圈V.TIF"\*MERGEFORMATINCLUDEPICTURE"E:\\鹿晴晴\\2015\\一轮\\Word\\一轮\\物理\\圈V.TIF"\*MERGEFORMATINETINCLUDEPICTURE"D:\\杨爱珍\\江苏\\word\\圈V.TIF"\*MERGEFORMATINET的读数变大，INCLUDEPICTURE"E:\\2015\\Word\\物理\\一轮物理\\圈A.TIF"\*MERGEFORMATINCLUDEPICTURE"E:\\2015\\Word\\物理\\一轮物理\\圈A.TIF"\*MERGEFORMATINCLUDEPICTURE"E:\\2015\\Word\\物理\\一轮物理\\圈A.TIF"\*MERGEFORMATINCLUDEPICTURE"E:\\鹿晴晴\\2015\\一轮\\Word\\一轮\\物理\\圈A.TIF"\*MERGEFORMATINETINCLUDEPICTURE"D:\\杨爱珍\\江苏\\word\\圈A.TIF"\*MERGEFORMATINET的读数变小B.INCLUDEPICTURE"E:\\2015\\Word\\物理\\一轮物理\\圈V.TIF"\*MERGEFORMATINCLUDEPICTURE"E:\\2015\\Word\\物理\\一轮物理\\圈V.TIF"\*MERGEFORMATINCLUDEPICTURE"E:\\2015\\Word\\物理\\一轮物理\\圈V.TIF"\*MERGEFORMATINCLUDEPICTURE"E:\\鹿晴晴\\2015\\一轮\\Word\\一轮\\物理\\圈V.TIF"\*MERGEFORMATINETINCLUDEPICTURE"D:\\杨爱珍\\江苏\\word\\圈V.TIF"\*MERGEFORMATINET的读数变大，INCLUDEPICTURE"E:\\2015\\Word\\物理\\一轮物理\\圈A.TIF"\*MERGEFORMATINCLUDEPICTURE"E:\\2015\\Word\\物理\\一轮物理\\圈A.TIF"\*MERGEFORMATINCLUDEPICTURE"E:\\2015\\Word\\物理\\一轮物理\\圈A.TIF"\*MERGEFORMATINCLUDEPICTURE"E:\\鹿晴晴\\2015\\一轮\\Word\\一轮\\物理\\圈A.TIF"\*MERGEFORMATINETINCLUDEPICTURE"D:\\杨爱珍\\江苏\\word\\圈A.TIF"\*MERGEFORMATINET的读数变大C.INCLUDEPICTURE"E:\\2015\\Word\\物理\\一轮物理\\圈V.TIF"\*MERGEFORMATINCLUDEPICTURE"E:\\2015\\Word\\物理\\一轮物理\\圈V.TIF"\*MERGEFORMATINCLUDEPICTURE"E:\\2015\\Word\\物理\\一轮物理\\圈V.TIF"\*MERGEFORMATINCLUDEPICTURE"E:\\鹿晴晴\\2015\\一轮\\Word\\一轮\\物理\\圈V.TIF"\*MERGEFORMATINETINCLUDEPICTURE"D:\\杨爱珍\\江苏\\word\\圈V.TIF"\*MERGEFORMATINET的读数变小，INCLUDEPICTURE"E:\\2015\\Word\\物理\\一轮物理\\圈A...
