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標題: alternating current 問題 [打印本頁]

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作者: cellmembrane    時間: 5/10/2011 03:52 PM
標題: alternating current 問題
The rms value of a sinusoidal ac voltage is 110v and its frequency is 60Hz . The voltage is applied across a20ohm resistor
a)express the voltage v as a function of time t
b)calculate the instantaneous power dissipated in the resistor at t=2 ms.

Thx!

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作者: Ivanhy92    時間: 5/10/2011 04:07 PM


a) For sinosoidal signal, V[peak] = sqrt2 V[rms]
Hence, V(t)
= V[peak] sin(ωt)
= sqrt2 V[rms] sin(2πf t)       (since ω=2πf )
= 110sqrt2 sin(120πt)

b) (懷疑DSE out-syl.?)
Since V[across R] is in phase with I[across R], and V=IR by Ohm's Law,
P(t) = V(t)I(t) = [V(t)]^2/R
=[110sqrt2 sin(120πt)]^2/R
=1210 sin^2(120πt)

P(2x10^-3) = ......

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作者: cellmembrane    時間: 5/10/2011 07:41 PM
我計到0.210W
但係書答案係570W

請問係咪我計錯左D咩?

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作者: Ivanhy92    時間: 5/10/2011 07:47 PM

我計到0.210W
但係書答案係570W

請問係咪我計錯左D咩?
cellmembrane 發表於 5/10/2011 19:41

                               
登錄/註冊後可看大圖

入sine function小心計數機有冇轉radian mode
因為你果個答案係degree mode計出的

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作者: cellmembrane    時間: 5/10/2011 09:57 PM
oh,原來係咁
唔該哂!!

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