# Voltage drop across paralell resistor and capacitor

by teroenza
Tags: capacitor, paralell, resistor, voltage
 P: 126 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 C= 0.001Farads freq.= 60Hz=377rad/s 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.
Mentor
P: 11,689
 Quote by 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 C= 0.001Farads freq.= 60Hz=377rad/s 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.
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.
 P: 126 To be sure I fully understand, by magnitude you mean take the square root of (my complex quantity * its complex conjugate) ?
Mentor
P: 11,689
Voltage drop across paralell resistor and capacitor

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

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