# Voltage drop across paralell resistor and capacitor

1. Feb 24, 2012

### teroenza

1. The problem statement, all variables and given/known data
Find the voltage drop across a resistor and capacitor in parallel. I am trying to understand how to deal with this using complex numbers. I may have a completely wrong notion of complex impedance. I thought I could treat the complex impedance like resistance, then take the modulus or real part (I believe I know the math, but not which to apply).

I= 100 milli Amps
R= 1000 ohms

2. Relevant equations
Z_c=1/(i*omega*C)

R_eq= (R*Z_C)/(R+Z_C)

3. The attempt at a solution
Do I apply the standard resistors in parallel formula then take the real part of the modulus? Or do I have a completely wrong conception on complex impedance.

2. Feb 24, 2012

### Staff: Mentor

Calculate the complex impedance as you've suggested using the 'usual' formula for resistors in parallel. Apply Ohm's law to find the (complex) voltage that will appear across the net impedance when driven by the 100mA current. The magnitude of that complex quantity should be what you're looking for.

3. Feb 26, 2012

### teroenza

To be sure I fully understand, by magnitude you mean take the square root of (my complex quantity * its complex conjugate) ?

4. Feb 26, 2012

Yes.