# Simple Question

1. Jun 8, 2007

### neelakash

A little bit of confusion:

Is it not correct to write ▼. E=ρ/ε0 inside a dielectric body.
As far as I know we should write ε instead of ε0.[where ε=εr*ε0]
Then why do we write ▼. E=ρ/ε0 inside a conductor?

2. Jun 8, 2007

### lalbatros

Are the dimensions correct in this equation: E=ρ/ε0 ?
I don't think so since an electric field from a charge is given by:

E = q/(4 pi ε0 r²) and since q/r² is no a charge density.

This can also be looked at from physical point of view.

3. Jun 8, 2007

### neutrino

He is referring to the differential form of Gauss' Law. I think you are not seeing the $\nabla$ in the OP, it seems to be black inverted triangle.

4. Jun 8, 2007

### ZapperZ

Staff Emeritus
When you deal with dielectrics, use D instead of E. This would be the most general form and will be true, even when you "simplify" it to the vacuum case. Only in the end do you need to do a quick conversion to E. This way, you don't have to worry about all your permitivity.

Zz.

5. Jun 8, 2007

### neelakash

Yes!that is a way to avoid the uneasiness.

But my question is why I can write ▼. E=ρ/ε0 inside a conductor?

6. Jun 8, 2007

### ZapperZ

Staff Emeritus
Because BY DEFINITION, under an electrostatic condition, E=0 inside a conductor.

Zz.