# Homework Help: Multisim rms current and voltage RLC Circuit

1. May 22, 2013

### k31453

Trying to find rms current at resonance and rms voltage across each elements (resistor, inductor and capacitor)

I got the answers but i want it do in multisim !!

i got :

R = 500 ohm
L = 0.40mH
C = 100pF

rms current: 0.002A
rms voltage:
Vr = 1V
Vc = 126.52 V
Vl = 126.52 V

The resonant freq. is 25.16 Khz at 1v RMS ac source.

[Broken]
this is my attempt !!!
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

Last edited by a moderator: May 6, 2017
2. May 22, 2013

### Staff: Mentor

How did you arrive at the resonant frequency? It looks a bit small to me, given the stated component values.

3. May 22, 2013

### k31453

A) resonant frequency
ans: f = 1/2*pi*sqrt(LC)
= 1/(2*pi*sqrt(0.0004 * 100 * 10^-12)
= 795.77 Khz

b) the inductive and capacitive reactance at resonance
ans: XL = 2*pi*f*L
= 2*pi* 795.775*10^3*0.0004
= 2000 ohm

Xc = 1/(2*pi*f*C)
= 1/(2*pi* 795.775*10^3 * 100 * 10^-12)
= 1999.9998 ohm

C) the impedance at resonance

ans : impedence of resonance is resistance of circuit : z = R = 500 ohm

D) the rms current at resonance
ans: I = V/R = 1/500 = 0.002A

E) the rms voltage across each element at resonance
Ans: Vr = IR
= 0.002 * 500
= 1V

VL = IXL
= 0.002 * 2000
= 4V

Vc = IXc
= 0.002 * 1999.99
= 3.99998 V

4. May 22, 2013

### Staff: Mentor

Yes, that looks better.

5. May 22, 2013

### k31453

but still i cant prove into multisim !!!

6. May 22, 2013

### Staff: Mentor

I don't have Multisim, so I can't help with the details of using it. Sorry.

But looking at the image you've provided, I would say that there sure are a lot of multimeters inserted, presumably to measure current. Surely one would suffice for a series circuit? Also, it appears that the inductor's top end is open circuited and it is being bypassed by a multipmeter (to measure voltage?). I'd suggest removing all but one multimeter to measure the series current, and make sure that the circuit is unbroken and operational before adding multimeters in parallel with the components to measure their voltages.