The problem of power
2008-01-04 5:19 am
A filament bulb rated '220V,60W'is connected to a 110V power supply.Estimate the output power of the light bulb.Assume that the resistance of the filament is the same as that when the light bulb is working at its rated power.
回答 (2)
2008-01-04 6:03 am
✔ 最佳答案
First, find the resistance :P = V^2 / R
60 = 220^2 / R
R = 806.667 ohms
Then,
P = V^2 / R
= 110^2 / 806.667
= 15W
2008-01-03 22:05:34 補充：
The formula P = V^2 / R is derived from Ohms Law: I = V / RAs you know, P = IV, soP = ( V / R )( V )= V^2 / R
2008-01-05 00:31:31 補充：
Here is a summary of the steps to solve the question:(1) find the resitance of the bulb(2) find the power of the bulb when it is connected to 110V Both make use of the formula P = V^2 / R
參考: My Phy Knowledge
2008-01-05 4:50 am
用220V60W既燈泡接110V時燈泡既功率，你應該先搵出燈泡既電阻值
R = V² / P
= 220² / 60
= 48400 / 60
R = 806.667 Ω
然後再去搵燈泡接110V既功率,
P = V² / R
= 110² / 806.667
= 12100 / 806.667
P = 15W
R = V² / P
= 220² / 60
= 48400 / 60
R = 806.667 Ω
然後再去搵燈泡接110V既功率,
P = V² / R
= 110² / 806.667
= 12100 / 806.667
P = 15W
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