alternating current 問題

cellmembrane

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!

Ivanhy92

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) = ......

cellmembrane

我計到0.210W
但係書答案係570W

請問係咪我計錯左D咩?

Ivanhy92

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

cellmembrane

oh,原來係咁
唔該哂!!