# Permeability Of Light

1. Feb 28, 2005

### mustaffarel

What does a substance's permeability of light depend on?

2. Feb 28, 2005

### Integral

Staff Emeritus
The permeability of free space,or the permeability of a substance, is the parameter that determines how the substance effects a magnetic field. It does not just apply to light but to all magnetic fields

3. Feb 28, 2005

### mustaffarel

Is it because of visible light is a kind of electromagnetic wave?

4. Feb 28, 2005

### kirovman

Visible light is only a small part of the Electromagnetic wave spectrum, ranging from radio waves, up to X-rays and Gamma Rays, with visible light somewhere in the middle of the scale.

The parameter $$\mu_o$$ is the permeability of free space.
$$\mu_r$$ is the relative permeability (analogous to $$\epsilon_r$$)

It can be defined as $$B=\mu_0 (H+M)$$

Where B is the magentic induction field, H is the magnetic field strength and M is the magnetisation across the sample.
or with some working:

$$B = \mu_0 \mu_r H$$

Since $$M = \chi_m H$$
and $$\mu_r = (1+\chi_m)$$
($$\chi_m$$ is magnetic susceptibility)
relative permeability in a material is just some kind of a measure of how much of an applied magnetic field will be "used up" due to magnetisation in the material.

Also it is said that B is what you pay for, H is what you get.

Last edited: Feb 28, 2005