# Electrons and magnetic fields

1. Feb 24, 2016

### Billmyk

is it correct that if free floating electrons enter a magnetic field @ a right angle to the field they will take a
circular orbit around such field?

2. Feb 24, 2016

### jfizzix

That is what the Lorentz force law would tell us:
$\vec{F}=q \vec{v}\times\vec{B}$

The Force a free floating electron would experience due to the magnetic field would be perpendicular to both its current velocity and the direction of the magnetic field. Since this force is constant in magnitude and always perpendicular in direction, you can expect the electron to (at least to a good approximation) take a circular trajectory while inside this constant magnetic field.

I've heard more fully relativistic treatments of the electron trajectory aren't quite this simple, but it remains a good approximation, so long as the electron isn't moving close to the speed of light.

3. Feb 25, 2016

### Staff: Mentor

They don't do an orbit "around" a field, they would follow a circular path in the field. It cannot be a full circle with a static homogeneous field however, if the electrons enter it at some point they have to leave it again (because they would arrive at the same point of entrance again later).