# Magnitude of force on electron in magnetic field

1. Oct 13, 2013

### jaydnul

1. The problem statement, all variables and given/known data
An electron in a vacuum is first accelerated by a voltage of 41300 V and then enters a region in which there is a uniform magnetic field of .145 T at right angles to the direction of the electron's motion.

What is the magnitude of the force on the electron due to the magnetic field?
2. Relevant equations
$F=qvBsinθ$
3. The attempt at a solution
At first I though the 41300 V was just a number to throw me off (they do that a lot), but now I think it is important. I know the charge, magnetic field, and sin90=1. So the only thing I'm missing is velocity, but I have no clue how to calculate that from the information I was given. Any help?

Thanks

2. Oct 13, 2013

### Legaldose

You can find the energy of an electron by using qV = U, where U is the Kinetic Energy of the particle. Then it's just a matter of solving for v from the KE equation.

EDIT: I should point out that the energy will be in eV, which you can then just use a conversion factor to get it into joules.

3. Oct 14, 2013

### rude man

The electron is moving fast enough to warrant relativistic correction for calculating the velocity.

4. Oct 14, 2013

### jaydnul

Perfect. Thanks