# Homework Help: Power dissipated in the inductor

1. Feb 7, 2009

### noppawit

In RL, AC circuit, an AC source vst = 220sin(40000t-45°) is connected to a 60mH inductor and a 3kΩ resistor.

Show that the power dissipated in the inductor is zero.

The current in this circuit is 0.057A as I calclulated. I know that inductor has no charging role in this circuit. But how can I write, describe this by equation?

Thank you.

2. Feb 8, 2009

### Phrak

You need to find the power over one cycle, (or an integral number if you choose).

$$P = \int v(t)i(t)dt$$

3. Feb 8, 2009

### noppawit

Would you please make it simpler? I have not learned this before. I learned that

$$P_{avg} = V_{rms}I_{rms}cos(\theta) = V_{rms}I_{rms}\frac{R}{Z}$$

only.

4. Feb 8, 2009

### Phrak

You need to calculate both the current through, and the voltage across the inductor as a functions of time.

Inductors, being what they are, you should find that they are 90 degrees out of phase.

Since this is homework, you need to show some work. Generally, the more work the more help.