f2.cham. - Ans.fyi 參考答案

f2.cham.

ShikaP

2011-03-26 3:06 pm

如图所示，一个白炽灯泡L标有“4V 4W”字样，将它与一个定值电阻R0串联后接入电源电压为6V的电路中，测得R0消耗的电功率为2W，此时灯泡未正常发光，不记温度对灯泡阻值的影响，求：

1）灯泡L的电阻值
2）定值电阻R0电阻值
3）灯泡L的实际电功率
http://pic.wenwen.soso.com/p/20110325/20110325205735-171415389.jpg

更新1:

sor it's phys.

回答 (1)

天同

2011-03-26 6:40 pm

✔ 最佳答案

(1) Power = voltage^2/resistanceresistance of bulb = voltage^2/power = 4^2/4 ohms = 4 ohms

(2) Current of circuit = 6/(4 + Ro)
power consumed by Ro = [6/(4+Ro)]^2 x Ro
i.e. 2 = (Ro).[6/(4+Ro)]^2
2.(4+Ro)^2 = 36.Ro
(Ro)^2 - 10(Ro) + 16 = 0
solve for Ro gives Ro = 2 ohms (rejected) or 8 ohms
[the 2-ohms result is rejected because under this situation, the voltage across the bulb is 6 x (4/(2+4)) v = 4 v. The bulb would give the normal brightness]

Hence, resistance of Ro = 8 ohms

(3) Voltage across bulb = 6 x [4/(4+8)] v = 2 v
Actual power of bulb = 2^2/4 w = 1 w

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