Peak value or rms?


by leolaw
Tags: peak
leolaw
leolaw is offline
#1
Apr6-05, 01:57 AM
P: 86
I am always confused with rms value and peak value, so here is the problem:

What will be the peak value of the current of a well-insulated [tex]0.03\mu F[/tex] capacitor connected to a 2.0-kV(rms) 720-Hz line?

So first I find the reactance of the capacitor, which is:
[tex]X_c=\frac{1}{2\pi fC}[/tex]
[tex]7.4k \Omega[/tex]

and then [tex]V_{rms} = I_rms * X_c[/tex]
[tex] 2*10^3 = I_{rms} (7.4 * 10^3)[/tex]
[tex] I_{rms} = 2.7 * 10^{-1} A[/tex]

so is this the right answer, or do i have to multiply it by [tex]\sqrt{2}[/tex] to get the peak value?
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ehild
ehild is offline
#2
Apr6-05, 02:49 AM
HW Helper
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P: 9,818
Quote Quote by leolaw
I am always confused with rms value and peak value, so here is the problem:

What will be the peak value of the current of a well-insulated [tex]0.03\mu F[/tex] capacitor connected to a 2.0-kV(rms) 720-Hz line?
....
[tex] I_{rms} = 2.7 * 10^{-1} A[/tex]

so is this the right answer, or do i have to multiply it by [tex]\sqrt{2}[/tex] to get the peak value?

The peak value is sqrt(2) times the rms value, and the peak was asked....


ehild
thomate1
thomate1 is offline
#3
Apr6-05, 03:29 AM
P: 49
Yes he is correct. Since current can be described in the form of a sin fn, the maximum amplitude obtained is known as peak value. rms value is the root mean square value of all individual values

For eg, peak value of sin(x) is 1. But it takes values from -1 to 1. rms value=1/sqrt(2).
It is the net effect.


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