# Electric susceptibility vs relative permitivity

1. Mar 2, 2013

### Nikitin

So for dielectrics, electric susceptibility (χ) is just the relative permittivity of the dielectric (κ) minus one?
=> χ = κ -1?

Why? Doesn't this mean χ is a completely pointless constant? Just a different way to write κ?

2. Mar 2, 2013

### DrDu

Yes, it is simply sometimes convenient not to have to write -1 all the time.

3. Mar 2, 2013

### Meir Achuz

$${\bf P=\chi E}$$.
$${\bf D=\kappa\epsilon_0 E}$$.
$\chi$ and $\kappa$ are used in different relations.

Last edited: Mar 2, 2013