# Find current at high/low frequency

1. ### Acuben

61
1. The problem statement, all variables and given/known data
find the rms current delievered by the 45v (rms) power supply when
a) the frequency is very large
and b) the frequency is very small.

http://yfrog.com/jucurrentqg

2. Relevant equations
w= angular velocity (supposed to be omega)
L= inductor
C= capacitor
j= complex coefficent = sqrt(-1)
Zl= resistance of inductor
Zc= resistance of capacitor
Ztot= total resistance
R= resistance of resistor
P= Power

Xl=wL
Xc=1/wc
Zl=j*Xl
Zc=-j*Xc
Ztot= R + Zl + Zc = R + j(Xl-Xc)

3. The attempt at a solution

with frequency just being high, how am I supposed to get these exact numbers without letters/symbol for I? o.o I tried the calculation and omega did not cancel out either.

2. ### zhermes

The key idea is that in the case of very high or very low frequency, you can take the impedance (resistance) of the inductor and capacitor to be ~infinite, respectively. Does it make sense why that's true (as an approximation at least)?

In effect, this eliminates one of the two loops in the circuit for each case.

3. ### Acuben

61
ah yes it does, at first I thought the resistance would skyrocket to infinity / 0
thank you

Last edited: Oct 4, 2010