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    14.素養(4)
1 如圖所示電路,若電源Vs提供40mW功率,且V1=0.25Vs,則下列何者正確? 109 統測
A Is=2mA
B Vs=20V
C R=10 kΩ
D R 消耗20mW功率

電阻串聯時,電阻越大,分到的電壓越大。設串聯後的總電阻=Rt

10k:0.25Vs = Rt:Vs

Rt = 40kΩ

R = 40k-8k-10k-12k = 10kΩ

Vs提供40mW功率

Vs2 / Rt = 40m

Vs2 = 40m × 40k

Vs = 40V

Is = 40/40k =1mA

R 消耗功率 PR=1m × 1m × 10k =10mW