Eddy current losses - solid/laminated cores

[satchmo05]

Homework Statement

[PLAIN]http://img94.imageshack.us/img94/224/92898534.jpg
The figures show two types of magnetic cores that lie along the z-axis. The solid core has length L, radius a, and conductivity σ. Laminated core has N filametary cylinders each with length L and conductivity σ. If B = B_ocosωt a_z is directed upward and the filamentary cylinders fill 90% volume of solid core, find:
a.) the average eddy-current power loss in the solid core
b.) the average eddy-current power loss in each of the filamentary cores.
c.) the average eddy-current power loss in the total laminated core.

Assume the B-field is uniform throughout both solid and laminated cores.

Homework Equations

This is the problem, I don't know what formulas I should be using!

The Attempt at a Solution

Just an attempt, this is probably way off. It I attempt to find J within the cylinder, than J = σE. I know that ∇xE = -d(B)/dt. This way I can solve E, and plug it into the formula I have started with, giving me J. What would I do from here though!? Is this even the right way?! Please help! I appreciate all help in advance!

 

[marcusl]

For the first core, you need to know the skin depth. Have you covered that in class yet?

 

[satchmo05]

no, we have not.