| ||
| P额 |
| (6V)2 |
| 3.6W |
B、当滑片P移至a端时，电路中只有灯L，I=0.6A，电源电压U=IR=0.6A×10Ω=6V，故B错；
C、当滑片P移至b端时，滑动变阻器全连入为电阻R，灯L和R串联，UR=4V，UL=U-UR=6V-4V=2V，
∵I＝
| UR |
| R |
| UL |
| RL |
∴R＝
| URRL |
| UL |
| 4V×10Ω |
| 2V |
D、UR=4V，R=5Ω，PR＝
| ||
| R |
| (4V)2 |
| 20Ω |
故选D．
A. 小灯泡灯丝电阻是6Ω
| ||
| P额 |
| (6V)2 |
| 3.6W |
| UR |
| R |
| UL |
| RL |
| URRL |
| UL |
| 4V×10Ω |
| 2V |
| ||
| R |
| (4V)2 |
| 20Ω |