# Have some really simply E/M questions

#### phattestlewt

I need help conceptualizing a few E/M questions.

Whats the difference between a magnetic field and a magnetic force? Is there a fomrula for magnetic field?

I know magnetic Force = qvB and for a conducting wire it can also be F=ILB

When using the right hand rule, the magnetic field, electric force, and velocity of particle are all perpendicular to each other.

Can the magnetic force and electric force exist in the same system/problem? I'm getting confused with application of magnetic field vs magnetic force. I know the magnetic field, magnetic force, and direction of a particle are all perpendicular so how does this relate to a right hand rule for example when you try to discern direction of a particle, magnetic field, and electric force?

I hope this makes sense.

#### pjk77

This may be hard to explain just by writing, but here's some info about this:

The magnetic force is the force exerted by the magnetic field on some particle, q, moving at velocity, v.
The equations to know are F (due to the magnetic field) =qvB for a moving charge (magnetic force only acts on moving charges) and F=ILB for a current carrying wire
Yes, a magnetic force and electric force can exist in the same problem. You would add the forces as F= qE + qvB where qE is the force due to the electric field on the particle of charge q and qvB is the magnetic force due to the magnetic field.
My way of using the RHR- use your RIGHT HAND (i've used left before): keep you hand FLAT and put in in the direction that the particle is moving, face palm towards direction of B field, thumb will be the direction of the force. You'll always know 2 to figure out the third, but usually you are trying to the force (so the thumb).
For the B field for a wire, grab the wire with your right hand so that your thumb points in the direction of the current. The B field makes rings around the wire.
For the electric field direction determinations, the E field is drawn from the positive charge to the negative charge (positive radiates out-- like a positive person). The force due to the E field is in the same direction when the charge is POSITIVE (this makes sense, because the force is trying to bring the positive particle to the negative side). If the charge is negative, the force is in the direction opposite of the E field (which makes a ton of sense because if its negative its going to want to be going towards the positive, while the E field is alway set up going from positive to negative).

That's a lot of random info, but hopefully you get something out of it. This is actually my favorite physics concept...