# Homework Help: Irms, Vrms and power calculations

1. Apr 12, 2012

### NoConflict

1. The problem statement, all variables and given/known data

Basically, I need to understand how to calculate Irms and I*rms given a Vrms and an impedance Z.

Example question:
Given Vrms = 120 V at an angle of 30° and an impedance of Z = 10 Ω, find Irms and I*rms.

2. Relevant equations

How exactly do I solve for Irms and I*rms?

3. The attempt at a solution

I figure that Irms = Vrms / Z. However I am a bit confused as to the I*rms.

From my notes, I would imply that I just flip the sign of the angle, but this does not seem right.

My attempt:

Irms = Vrms/Z = 120angle30/10angle0 = 12angle30
And for I*rms, just flip the sign of the angle: 12angle-30

2. Apr 12, 2012

### Staff: Mentor

Yup. basically that's it. I* represents the complex conjugate, which for a complex number means that the sign of the imaginary component of the number is inverted. This has the effect of inverting the sign of the angle in polar form.