# Charge moving through a magnetic field

1. Mar 12, 2004

### jasonrindy

I was wondering if anybody knows or has any ideas as to why the force on a charge as it moves through a magnetic field is perpendicular to the velocity and field direction. Thanks

2. Mar 12, 2004

### Cyclotron Boy

First answer: Because Maxwell's equations are constructed that way.

Second answer: Because it is what we experience.

Take for example a long thin wire oriented vertically with a current moving in the up direction. This would create a B field in the (+) theta-hat direction for a right handed coordiate system. Now, let's have another wire travelling parallel to the first, at some distance away. In this manner, the B field intersects the second wire perpendicularly. If a current is run parallel to the first wire in the second wire, the electrons moving in the wire feel an attractive force between the wires. This is a force that is perpendicular to the B field and the direction of the current. Thus: if a point charge moving along the path of the second wire replaces it in the above system, it acts just like the current in the wire. It similarly feels a force perpendicular both to its direction and the direction of the imposed B field.

Hope this helps.
-F

3. Mar 12, 2004

### Palpatine

Ive read an explanation of electrostatic forces where the momentum of virtual photons point back to the originating electron accounting for the attractive force between two electrons. Why a net force results is not clear to me. I would also like to know how these photons account for forces experienced by moving charges, and why neutral particles dont generate these same photons or if they do why they dont exhibit the same assymetrical behaviour.