# Homework Help: Help this problem cost me much time

1. Aug 14, 2006

### goodboy

english is my second language,if there are some wrong in the sentence ,don't laugh at me

dig a columniform cavity in a infinity uniformity magnetic medium.the

cavity's radius is r and the high is h,and the axis of the cavity parallels

the direction of magnetization M in the medium.
question:1)when h>>r,the magnetic field strength H of the point in the cavity = the magnetic field strength H in the medium.
2) when r>>h,the magnetic induction strength B of the point in the cavity = magnetic induction strength B in the medium.
haw to testify ?

2. Aug 16, 2006

### Andrew Mason

I'll start by trying to translate the question. Could you tell us what your first language is?

Make a cylindrical cavity through an infinitely large uniformly magnetic medium. The cylinder's radius is r and its height is h and the axis of the cylinder is parallel to the direction of the magnetic field in the medium.

Question:
1) when h>>r, the magnetic field strength H at any point in the cavity is equal to the magnetic field strength in the medium

2) where r>>h, the magnetic induction B of the point in the cylinder is equal to the magnetic induction B in the magnetic medium.

How do you explain this?​

Perhaps that will get a response for you.

AM

Last edited: Aug 16, 2006
3. Aug 16, 2006

### goodboy

thank you very much,my first language is chinese.i'm not good at english,don't laugh at me . there is no problem in your interpretation.

4. Aug 16, 2006

### Andrew Mason

Ok. I was a little unsure about the difference between magnetic induction and the magnetic field at first, but I think I understand the problem now.

The magnetic field strength H is the magnetic field that would exist in the absence of the magnetic material (ie in a vacuum), divided by $\mu_0$, the permeability of free space. The magnetic induction B, is the actual measured magnetic field (which depends on the permeability of the magnetic material). H represents a kind of fundamental magnitude of the magnetic field that is independent of the permeability of the material.

$$B = \mu H$$