（2008?房山区二模）如图所示电路，电源电压不变，R1的阻值为10Ω，闭合开关S，滑动变阻器的滑片滑到b点 如图所示电路，电源电压不变，R1的阻值为10欧，闭合开关S，...
\u5982\u56fe1\u6240\u793a\u7535\u8def\uff0c\u7535\u6e90\u7535\u538b\u4e0d\u53d8\uff0cR1\u7684\u963b\u503c\u4e3a10\u03a9\uff0c\u95ed\u5408\u5f00\u5173S\uff0c\u65ad\u5f00\u5f00\u5173S1\uff0c\u6ed1\u52a8\u53d8\u963b\u5668\u7684\u6ed1\u7247\u6ed1\u5230b\u7aef\uff0c\u7535\u538b\uff081\uff09\u95ed\u5408\u5f00\u5173S\uff0c\u6ed1\u52a8\u53d8\u963b\u5668\u7684\u6ed1\u7247\u6ed1\u5230b\u7aef\u65f6\uff0c\u7b49\u6548\u7535\u8def\u56fe\u5982\u56fe\u6240\u793a\uff1a\u56e0\u4e3aR1\u4e0eR2\u4e32\u8054\uff0c\u6240\u4ee5\u901a\u8fc7R1\u3001R2\u7684\u7535\u6d41\u76f8\u7b49\uff0c\u5373I1\uff1aI2=1\uff1a1\uff1b\uff082\uff09\u56e0\u4e3a\u7535\u538b\u8868V1\u548cV2\u793a\u6570\u4e4b\u6bd4\u4e3a5\uff1a7\uff0c\u4e14U=IR\uff0c\u6240\u4ee5U1+U2U1+Uab=R1+R2R1+Rab=10\u03a9+R210\u03a9+Rab=57\uff0c\u537320\u03a9+7R2=5Rab----------------------------\u2460\u56e0\u4e3aR2\u4e0eRab\u6d88\u8017\u7684\u529f\u7387\u4e4b\u548c\u662fR1\u6d88\u8017\u529f\u7387\u76844\u500d\uff0c\u6839\u636eP=I2R\uff0c\u6709I2\uff08R2+Rab\uff09=4I2R1\u53ef\u5f97\uff0cR2+Rab=40\u03a9---------------------------\u2461\u7531\u2460\u2461\u53ef\u5f97\uff1aR2=15\u03a9\uff0cRab=25\u03a9\uff1b\uff083\uff09\u95ed\u5408\u5f00\u5173S\u548cS1\uff0c\u53d8\u963b\u5668\u6ed1\u7247P\u6ed1\u5230b\u7aef\u65f6\u7684\u7b49\u6548\u7535\u8def\u5982\u56fe\u6240\u793a\uff1a\u7531\u56fe\u4e2d\u5f97\u77e5\uff0c\u5f53\u6ed1\u7247\u6ed1\u5230b\u7aef\u65f6\uff0c\u7535\u538b\u8868V2\u7684\u793a\u6570\u4e3a5V\uff0e\u5219\u7535\u6e90\u7535\u538b\u4e3a\uff1aU=IR\u603b=5V25\u03a9\u00d7\uff0825\u03a9+15\u03a9\uff09=8V\u5f53\u7535\u538b\u8868V2\u7684\u793a\u6570\u4e3a2V\u65f6\uff0cR2\u4e24\u7aef\u7535\u538b\uff1aU2\u2032=8V-2V=6VR2\u4e0a\u6d88\u8017\u7684\u529f\u7387\uff1aP2\u2032=U2\u20322R2=(6V)215\u03a9=2.4W\uff0e\u7b54\uff1a\uff081\uff09\u901a\u8fc7R1\u4e0eR2\u7684\u7535\u6d41\u4e4b\u6bd4\u4e3a1\uff1a1\uff1b\uff082\uff09\u6ed1\u52a8\u53d8\u963b\u5668\u7684\u6700\u5927\u963b\u503cRab\u4e3a25\u03a9\uff1b\uff083\uff09\u7535\u538b\u8868V2\u7684\u793a\u6570\u4e3a2V\u65f6\uff0c\u7535\u963bR2\u4e0a\u6d88\u8017\u7684\u529f\u7387\u4e3a2.4W\uff0e
I1 *\uff08R+R1+R2\uff09= Ec\uff1b
I1 *\uff08R1+R2\uff09\uff1aI1 *\uff08R1+R\uff09= 5\uff1a7\uff1b
I1 * R2 * I1 + I1 * R * I1 = 4 * I1 * I1 * R1 ==> R2+R=4R1\uff1b
\u4ee5\u4e0a\u662f\u5927\u6982\u7684\u5173\u7cfb\u5f0f\uff1b\u81ea\u5df1\u53bb\u6c42\u89e3\u51fa\uff1aR\uff0cR2\uff0c\uff08Ec\uff09\u6765\uff1b
\u3010\u6c42\uff1a\u901a\u8fc7R1\u548cR2\u7684\u7535\u6d41\u6bd4\u3011 \u4e5f\u592a\u7b80\u5355\u4e86\uff0c\u662f\u4e0d\u662f\u4f60\u5199\u9519\u4e86\uff1f\uff1f
∵R1与R2串联，
∴通过R1、R2的电流相等，即
| I1 |
| I2 |
| 1 |
| 1 |
（2）∵V1：V2=5：7，且U=IR，
∴
| U1+U2 |
| U1+Uab |
| R1+R2 |
| R1+Rab |
| 10Ω+R2 |
| 10Ω+Rab |
| 5 |
| 7 |
即20Ω+7R2=5Rab----------------------------①
∵R2与Rab消耗的功率之和是R1消耗功率的4倍，且P=I2R，
∴
| P2+Pab |
| P1 |
| R2+Rab |
| R1 |
| R2+Rab |
| 10Ω |
即R2+Rab=40Ω---------------------------②
由①②可得：R2=15Ω，Rab=25Ω．
（3）当滑片移动到b点时，R1消耗的功率P1=I12R1=(
| U |
| R1+R2+Rab |
当滑片移动到a点时，等效电路图如图所示：
R1消耗的功率P1′=（I1′）2R1=(
| U |
| R1+R2 |
所以
|
