# Homework Help: Solenoid equation derivations

1. Sep 24, 2008

### nissanztt90

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

Consider a solenoid of length L, transverse area A, total number of loops N

Compute the magnetic field B inside the solenoid, assuming that it is uniform and vanishes outside the solenoid, neglect any boundary effects.

Working under the same assumptions, calculate the total energy input necessary to turn on an electric current through the solenoid from 0 to a final value I. This computation must involve an integral.

2. Relevant equations

I need to derive B = u0 (N/l) I for the first part.

3. The attempt at a solution

I dont really know where to start, thats really all i need is a starting point. Im a bit confused, so if someone knows which equations to use/or start with that would be a big help.

For example i had another problem where i had to compute the electric field E in a parallel plate capacitor...needed to derive E = Q/($$\epsilon$$0A), but i had V=Ed, V=Q/C, and C = ($$\epsilon$$0A)/d to start with.

Last edited: Sep 24, 2008
2. Sep 25, 2008

### muppet

Do you know Ampere's Law?
If so, think about what kind of path you'd need to use for it to be helpful.