...断开开关S3,分别只闭合开关S1和只闭合开关S2时电阻R1和R2两端的...

只闭合开关S1时，等效电路如图1所示
只闭合开关S2时，等效电路如图2所示
开关S1、S2、S3都闭合时，等效电路如图3所示

（1）由图1和图2可知对于同一电阻R3，根据欧姆定律可得：
I1I2=U3R3U′3R3=U3U3′=23，
∵电阻R1和R2两端的电压之比为4：3，
∴U1U2=I1R1I2R2=I1I2×R1R2=23×R1R2=43，
解得：R1R2=21，
∵电源的电压不变，
∴根据串联电路的特点可得：U=I1（R1+R3）=I2（R2+R3），
∴R2=R3，R1=2R3，
∵P=I2R，
∴P1P3=R已赞过已踩过你对这个回答的评价是？评论收起 ._1uevpeq{zoom:1;background-color:#fff;border:0;margin-bottom:10px;padding:30px 0 20px 42px;position:relative}._1uevpeq.ec-1841{padding:20px 0}._1uevpeq.ec-2246{padding:20px 0 10px}.ec-1841 .y7we4hu{font-size:16px;margin-bottom:-5px}.y7we4hu{color:#7a8f9a;height:25px;line-height:25px;overflow:hidden;position:relative}.y7we4hu h2{margin:0;padding:0}.y7we4hu:after{clear:both;content:" ";display:block;height:0;visibility:hidden}a.tycfu7u{color:#666;float:right;font-size:12px;margin-left:8px;text-decoration:none}.hhhv6ex{color:#666;font-size:13px;line-height:normal;line-height:20px;margin-top:10px}.vnsdjzp{margin-top:15px;position:relative}.vnsdjzp h3{font-weight:400;padding:0}.vnsdjzp a{text-decoration:none}.vnsdjzp em{color:#d81419;font-style:normal}.ec-2246 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