# What is the direction of the force on an electron moving south in a magnetic field that points west?

a. Down

b. East

c. North

d. Up

I think we're supposed to know the Right-Hand rule for this so if you know how to figure this out with this rule could you explain how? Thank you!

### 1 Answer

- UniversalistLv 71 decade agoBest Answer
The magnitude of the induced force is F = q V x B (q times V cross B) where q is the magnitude of the electric charge, V is the moving charge velocity, and B is the magnetic field strength (V and B are both vectors). The right hand rule says if you keep your fingers in the direction of the motion (velocity) with the field lines pointing out of your palm, then your thumb will give the direction of the induced force. In your problem, this implies the force is pointing into the paper (or monitor) perpendicular to the plane that is determined by V and B (this direction is a result of the definition of the vector cross product). If you draw the situation you will see things more clearly. The answer is a. (down).