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1、7 闭合电路的欧姆定律Evaluation only.Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0.Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd.Copyright 2004-2011 Aspose Pty Ltd.复习回顾: 1、什么是电源？2、电源电动势的概念?物理意义?把其它形式的能转换成电能的装置。（1）定义：在电源内部非静
2、电力做功把单位 正电荷从电源的负极移到正极所做的功。（2）意义：电动势表示电源将其他形式的能 转化为电能本领。3、如何计算电路中电能转化为其它形式的能？W = I U t对于纯电阻电路Evaluation only.Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0.Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd.Copyright 200
3、4-2011 Aspose Pty Ltd.一、闭合电路用导线把电源、用电器连成一个闭合电路。外电路:电源外部的用电器和导线构成外电路. 内电路:电源内部是内电路.rERK内电路外电路Evaluation only.Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0.Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd.Copyright 200
4、4-2011 Aspose Pty Ltd.在外电路中，电流方向由正极流 向负极，沿电流方向电势降低。在内电路中，即在电源内部，通过 非静电力做功使正电荷由负极移到正 极，所以电流方向为负极流向正极。闭合回路的电流方向内电路与外电路中的总电流是相 同的。Evaluation only.Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0.Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 200
5、4-2011 Aspose Pty Ltd.Copyright 2004-2011 Aspose Pty Ltd.1、电路中的电势变化情况（1）在外电路中，沿电流方向电势降低 。 （2）在内电路中，一方面，存在内阻， 沿电流方向电势也降低；另一方面，沿 电流方向存在电势“跃升”。Evaluation only.Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0.Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0.
6、Copyright 2004-2011 Aspose Pty Ltd.Copyright 2004-2011 Aspose Pty Ltd.bdacababcd4电动势概念电动势概念 的理解的理解Evaluation only.Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0.Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd.Copyrig
7、ht 2004-2011 Aspose Pty Ltd.2.讨论闭合回路中的能量转化关系1、若外电路中的用电器都是纯电阻R，在时间t内外 电路中有多少电能转化为内能？rERK内电路外电路E外=I2Rt2、内电路也有电阻r，当电流通过内 电路时，也有一部分电能转化为内能 ，是多少？E内=I2rt3、电流流经电源时，在时间t内 非静电力做多少功W=EqEIt4、以上各能量之间有什么关系？Evaluation only.Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0.Created wit
8、h Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd.Copyright 2004-2011 Aspose Pty Ltd.根据能量守恒定律，非静电力做的 功应该等于内外电路中电能转化为其 他形式的能的总和。W=E外+E内即：EIt=I2Rt+I2rtEvaluation only.Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0.Created with Aspo
9、se.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd.Copyright 2004-2011 Aspose Pty Ltd.、表述：闭合电路中的电流跟电源 的电动势成正比，跟内、外电路的电 阻之和成反比、3、闭合电路欧姆定律Evaluation only.Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0.Created with Aspose.Slides for .NET 3
10、.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd.Copyright 2004-2011 Aspose Pty Ltd.说明：二、闭合电路欧姆定律 ：2、 是外电路上总的电势降落 ，习惯上叫路端电压.3、 是内电路上的电势降落， 习惯上叫内电压.4、1、只适用于纯电阻电路Evaluation only.Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0.Created with Aspose.Slides for
11、.NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd.Copyright 2004-2011 Aspose Pty Ltd.1、在如图所示的电路中，电源的电动 势为 9V，内阻为0.5，外电路的电 阻R1为18， 求电路中的电流和路端 电压.若将电阻换为R2=36，情况如 何？ RSEr课堂训练Evaluation only.Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0.Created with As
12、pose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd.Copyright 2004-2011 Aspose Pty Ltd.外电路两端的电压叫路端电压、如图电路：R增大，电流减小，路端电压增大R减小，电流增大，路端电压减小路端电压:二、路端电压跟负载的关系Evaluation only.Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0.Created with Aspose
13、.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd.Copyright 2004-2011 Aspose Pty Ltd.、两个特例 ：（2）外电路短路时（1）外电路断路时Evaluation only.Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0.Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0.
14、Copyright 2004-2011 Aspose Pty Ltd.Copyright 2004-2011 Aspose Pty Ltd.ababbdca5b dca Evaluation only.Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0.Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd.Copyright 2004-2011
15、Aspose Pty Ltd.、电源的外特性曲线路端电压 U随电流I变化的图象 （1）图象的函数表达： Evaluation only.Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0.Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd.Copyright 2004-2011 Aspose Pty Ltd.（2）图象的物理意义在纵轴上的截距表
16、示电源的电动势E 在横轴上的截距表示电源的短路电流图象斜率的绝对值表示 电源的内阻，内阻越大， 图线倾斜得越厉害Evaluation only.Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0.Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd.Copyright 2004-2011 Aspose Pty Ltd.小结 1闭合电路欧姆定律 2路端电压跟负载的关系： （1）表述：闭合电路中的电流跟电源的电动势成正 比，跟内、外电路的电阻之和成反比（2）表达式（1）路端电压随外电路电阻R增大而增大 断路短路（2）路端电压U随电流I变化的图象 Evaluation only.Evaluation only. Created with Aspose.Slides
