# Fields generated by a rotating disk

1. Sep 1, 2012

### lailola

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

We have an uniformly charged disk with total charge q, which is rotating around its axis with constant angular velocity w. Calculate electric and magnetic field in the axis and in the rotation plane. Calculate the radiated power in one cicle.

2. Relevant equations

Biot-Savart law.
v=wr

3. The attempt at a solution

I only know how to calculate the magnetic field in the center, using directly the biot-savart law:

$d\vec{B}=\frac{\mu}{4\pi}dq\frac{\vec{v}×\hat{r}}{r^2}$
$B=∫_{0}^{a} \frac{\mu}{4\pi}\sigma 2\pi r dr\frac{wr}{r^2}=\frac{\mu w \sigma a}{2}=\frac{\mu w q}{2\pi a}$

How can I calculate the rest?

Thank you.

Last edited: Sep 1, 2012
2. Sep 1, 2012

### vela

Staff Emeritus
Your answer is wrong. For one thing, you should note your result is independent of where you are on the z-axis. That can't be right. Be a bit more careful about what each variable stands for in your integral.

3. Sep 1, 2012

### lailola

You're right, It's the field in the center.

4. Sep 1, 2012

### lailola

I've already calculated the magnetic field along the axis. But, in the plane? And, what about the electric field? Any help?

thanks