# Magnetic fields

1. Dec 9, 2007

### aurora14421

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

A proton enters a uniform magnetic field of strength B. Sketch it subsequent motion and derive an expression for the time, t, spent in the magnetic field.

2. Relevant equations

$$F=qvB=mv^{2}\div r$$

3. The attempt at a solution

I calculated the period of the particle in the field as:

$$T= 2 \pi m\div qB$$

I don't know if this is what they want or if there's a way to calculate the total time.

Last edited: Dec 9, 2007
2. Dec 14, 2007

### Shooting Star

Last edited by a moderator: Apr 23, 2017
3. Dec 14, 2007

### Astronuc

Staff Emeritus
A charged particle will spend 1/2 period in a magnetic field (assuming it's constant) when it enters at the boundary from a region without the magnetic field.