# Induced EMF through a coil How/Why?

1. Dec 13, 2011

### MickOtto

1. The problem statement, all variables and given/known data

In a lab I passed a magnet through a coil and measured the voltage.

I need/want to know why when moving a magnet through a coil you induce a current. I don't necessarily need a direct answer - I more just want to know if my argument holds and where to look if I'm completely off the mark. Note I am only dealing with classical physics.

I'm pretty ok with data. I managed to measure within the error bound what I was trying to.

2. Relevant equations
F = qv x B

3. The attempt at a solution

Ok, my theory relies mainly on the equation F = qv x B. I argue (in more detail) that as you pass a magnet through a coil, charged particles in the coil move with a velocity relative to the magnetic field. The edge effects of the magnetic field cause the charged particles to move in direction of the right hand rule, which induces a current and sets up a Voltage which is what I measured.

If this works then I'm happy with the rest of my theory. Due to a strange Summer Session timetable and me going on holidays last week I haven't actually learnt much about magnetic fields and we will be starting induction tomorrow. I hate to put it to the internet for help but I've got no where else, sorry.

Thanks for any help.
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

2. Dec 13, 2011

### Delphi51

Yes, F = qvB says a charge moving relative to a perpendicular magnetic field will experience a force proportional to v and B. No edge effect involved, though.

Perhaps it is instructive to realize that this is a basic observation. No one derived it from anything; this was one of the observational facts that led to the formulas later on.

3. Dec 13, 2011

### MickOtto

Hmm, whenever I do my right hand rule I end up with the 0 for the normal magnetic field. Maybe I have a different idea of what edge effects are..

Thanks for your help. Yes, I know it's not derived. This part is just me trying to explain what is happening. My derivations for other parts of the lab I'm happy with.

4. Dec 13, 2011

### Delphi51

Have you done the skipping wire experiment? Two people swing a wire around like a skipping rope. The wire is swinging through the Earth's magnetic field (which has no edge, at least near the wire) and you can observe the current if you connect it to a Galvanometer (or voltage if connected to a sensitive voltmeter). The current and voltage do not depend on any edge effect.