# Magnetic fields

## Homework Statement

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.

## Homework Equations

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

## 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.

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