人教版八下物理同步教学课件第七章欧姆定律四欧姆定律和安全用电[课件].ppt

Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. 基础梳理.知识点睛 Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. 导体 不高于36 V 越大 Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. 没有接通 不工作 电源两极 电源 温度升高 Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. 放电 大地 Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. 要点归纳.诱思探究 Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. 短路和断路的判断 1.判断方法： 连接方式 现象 故障 串联 至少有一个灯亮,其他灯不亮 不亮的灯短路 所有灯不亮 某处断路或电源短路 电流表无示数，电压表示数为电源电压. 电压表测量的那部分电路断路. Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. 并联 其中一只灯不亮 这个灯所在支路断路 所有灯都不亮 其中一个支路短路或干路断路 Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. 2.短路类型：(1)电源短路，如图甲所示，这是绝对不允许的；(2)部分短路，如图乙所示，这种情况有时可以允许. Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. 短路可能会造成电路中电流过大，会将用电器烧坏，是不允许的. Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. 【典例】在如图所示的电路中，闭合开关，调节滑动变阻器，发现两只电表中有一只电表的示数明显变小，另一只电表的示数明显变大.下列判断中正确的是 Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. A.可能是灯L断路 B.一定是灯L短路 C.可能是滑动变阻器R断路 D.一定是滑动变阻器R的滑片向左滑动 Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. 【解析】选A.本题考查学生对电路故障的分析判断能力.灯L断路时，电压表串联接入电路中，由于电压表的电阻极大，所以电路中电流极小，则电流表示数明显变小，电压表测量电源电压，示数明显变大；故A正确；当灯L短路时，电压表示数明显变小，电路中只有滑动变阻器，则电流表示数会变大，但B项说法太绝对，故B错误；变阻器断路时，电压