# Magnitude of force on electron in magnetic field

## Homework Statement

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?

## Homework Equations

$F=qvBsinθ$

## 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

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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.

rude man
Homework Helper
Gold Member
The electron is moving fast enough to warrant relativistic correction for calculating the velocity.

Perfect. Thanks