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1、1. 二个电阻 R1、R2 并联,干路总电流为 I ,问:通过每个电 阻的电流 I1、 I 2各是多少?想一想,并联电阻分流与各自的电阻有什么关系?,2. 二个电阻 R1、R2 串联,两端加电压为U ,问:每个电阻 两端的电压U 1、 U 2各是多少?想一想,串联电阻分压与各自的电阻有什么关系?,Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd.,3.如图所示电路,当ab两端接入100V电压时,cd两端为20V,当
2、cd两端接入100V电压时,ab两端电压为50V,则R1:R2:R3为( ),A.4:2:1 B.2:1:1 C.3:2:1 D.以上都不对,R1,R1,R2,R3,R3,a,b,c,d,A,100V,20V,40V,40V,100V,50V,25V,25V,Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd.,A.保持R2不变,增大R1 B.增大R1 ,减小R2 C.保持R2不变,减小R1 D.增大R2 ,减小R1
3、,4.如图所示,电流表G的内阻不可忽略不计,R1、R2是两个可变电阻,当a、b间的电压为4V时,电流表的指针G刚好满偏,当a、b间的电压为3V时,如果仍要使电流表G的指针满偏,下列方法中可行的是( ),AB,Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd.,9如图6所示,L1,L2是两个规格不同的灯泡,当它们如图连接时,恰好都能正常发光,设电路两端的电压保持不变,现将变阻器的滑片P向右移动过程中L1和L2两灯的亮
4、度变化情况是 ( ) AL1亮度不变,L2变暗 BL1变暗,L2变亮 CL1变亮,L2变暗 DL1变暗,L2亮度不变,B,Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd.,5.三个电阻R1=R2= 8 、 R3=4, UAB=2V如图所示连接, 求:(1)电路的总电阻.(2)两电流表的示数。,R总=2,0.75A,0.5A,Evaluation only. Created with Aspose.Slides f
5、or .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd.,6.四个电阻如图所示连接,若R1=R2=R3=R4=2,且R1两端的电压为4V,求:(1)电路的总电阻.(2)电阻R2两端的电压,R总=1.2,U2=6V,4A,Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd.,二. 滑动变阻器的分压式限流式,Evaluation onl
6、y. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd.,1.限流式,待测电阻Rx的电压可调范围,限流式电路的特点: 1.电压不能从零开始调节,调节范围较小. 但电路结构较为简单 2.电能损耗较小.,Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd.,2.分压式,待测电
7、阻Rx的电压可调范围,分压式电路的特点: 1.电压可以从零开始调节到电源电动势,调节范围较大. 但电路结构较为复杂. 2.电能损耗较大.,Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd.,电表的改装,Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose
8、Pty Ltd.,如图所示,电路由电流计与四个电阻连接而成.电流计内阻Rg=80,满偏电流Ig=1mA. R1=R2=10 ,R3=194 ,R4=790.若使用12接线柱电路可做电流表.量程为 .若使用13接线柱可做 表.量程为 .若使用14接线柱电路可做 表.量程为 .若使用15接线柱可做 表.量程为 .,电流,电压,电压,5mA,10mA,1V,5V,Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd.,A.两
9、只电表的指针偏转角相同 B.两只电表的指针都不偏转 C.电流表指针的偏转角小于电压表指针的偏转角 D.电流表指针的偏转角大于电压表指针的偏转角,用两只完全相同的电流表,分别改装成一只量程更大的电流表和一只电压表,将它们串联起来接入电路中,如图所示,此时( ),C,Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd.,一个电压表由表头G与电阻R串联而成,如图所示,若在使用中发现此电压表的读数总比准确值稍小一些,采用下列
10、哪种措施可能加以改进( ),A在R上串联一个比R小得多的电阻 B在R上串联一个比R大得多的电阻 C在R上并联一个比R小得多的电阻 D在R上并联一个比R大得多的电阻,分析:题中明确指出此电压表的读数总比准确值稍小,说明在电压表两端所加电压一定的情况下,电压表支路中的电流总是偏小校正的方法是适当减小电压表的内阻,而表头的内阻Rg,是确定的,所以只有适当减小分压电阻R在R上串联电阻是不行的并联一个电阻时,由于并联电路的总电阻比任何一个分电阻都小,可见不能并联小电阻,否则分压电阻的改变会很多,误差会更大,所以选项D正确,答案:D,Evaluation only. Created with Aspose
11、.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd.,二. 电流表的内外接,Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd.,平时怎样测量一个电阻?,1、安培表外接法,2、安培表内接法,Evaluation only. Created with Aspose.Slides for .NET 3.5 Clie
12、nt Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd.,系统误差分析,误差原因:因为电压表、电流表分别有分压分流的作用,它们本身的内阻会给电路造成影响从而带来误差,电流表外接法 R测= =R并=,U测,I测,U测,I总,R Rv,R+Rv,=,R,1+(R/Rv),当R RV时,R测 R 用 “外小 ” 两个字归纳: 即用电流表外接法测量的电阻远小于电压的内阻时结果较准确,而且测量值小于真实值, R,Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profil
13、e 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd.,电流表外接法,U测,U总,用“内大”两个字归纳:,即用电流表内接法测量的电阻远小于电压的内阻时结果较准确,而且测量值小于真实值,当RRA时,R测 R,Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd.,现欲测一阻值约为10的电阻,所用电压表内阻10K,所用电流表内阻1,那么应采用哪种测量电路?,采用电流表外接;,采用电流表
14、内接。,点触法也可用来判断安培表的内外接:,(1)接在a和b时伏特表示数有明显变化,则宜采用外接法;,(2)接在a和b时安培表示数有明显变化,则宜采用内接法.,比值比较法,Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd.,限流式,分压式,可调范围,变阻器,电能损耗,九、限流和分压电路的选取,较大阻值,较小阻值,较小,较大,Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd.,