# Why we use relative permeability

1. Nov 3, 2017

### janu203

Why we use relative permeability if we have absolute
permeability in electromagnetism?

2. Nov 3, 2017

### BvU

Because it's easier ?
Perhaps you want to show some examples where you think different ?

3. Nov 5, 2017

### janu203

I am more concerned regarding the theoretical aspect. Why cannot we just take absolute permeability of any material? In fact i have started reading about transformers and there i found relative permeability.

4. Nov 5, 2017

### BvU

Theoretical aspect ? Is $\vec B = \mu \vec H$ absolute enough ?
who is 'we ' ?
Who say we can not ?
I can't guess where you found this. Oherwise I could try to explain... Please tell us where.

5. Nov 6, 2017

### vanhees71

Well, while permittivity and permeability of the vacuum, $\epsilon_0$ and $\mu_0$ are mere conversion constants from unnatural SI units to natural units, $\epsilon_r$ and $\mu_r$ are effective physical properties of the material, derivable from the microscopic structure of it in terms of linear-response theory.

6. Nov 6, 2017

The relative permeability $\mu_r$ gives the factor that the magnetic field in the core material is increased by over the applied magnetic field from the current in the conductor coils of a solenoid or transformer. The absolute permeability $\mu=\mu_o \mu_r$ has an extra factor of $\mu_o$ in it, (in SI units), which obscures this simple result. $\\$ In c.g.s. units, $B=\mu H=\mu_r H$, this problem is absent, because $B=H+4 \pi M$, without any $\mu_o$ in front of the $H$.