# Need help with magnetic field question

1. Nov 10, 2009

### anon6912

This is a slide from my lecture illustrating how to find the magnetic field in a solonoid with an air gap.

I dont quite understand the following points:
What is the H field?
Whats the difference between the H field and the B field?
Why do you need them?

Other than that i understand how to do the integral and the evaluation. I just dont understand what the H field is.

EDIT: I attached a nother slide about the H field

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• ###### HB field 2.JPG
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2. Nov 10, 2009

### indie452

H is the magnetic field strength while B is the flux density. The strict definition of H is

H = B / μ0 - M where M is the magnetisation

However it is usually possible to simplify the calculation

H = B / μ

look at http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/magfield.html or search for "magnetic field strength H" and you will most likely find what you need