Proving Gradient of Electric Field in Coaxial Line Dielectric is 0

[renegade05]

Homework Statement

Show that (Grad dot E) =0 in the dielectric of a coaxial line.
(Hint: apply the divergence theorem to a portion of the dielectric.)

Homework Equations

Divergence theorem

The Attempt at a Solution

I think I need to show that grad dot E = p/epsilon = 0

I don't know - I'm stuck

 

[Simon Bridge]

I think I need to show that grad dot E = p/epsilon = 0

... Well that would be false wouldn't it?
Grad only applies to scalar fields. I think you mean "div" rather than grad.

Do you know the equation for the electric field of a coax line?
Do you know how to find the divergence of a vector field?

 

[Smoarzzz]

Apply the divergence theorem --- do EXACTLY what the hint tells you. Simply apply the divergence thm and take Ea to be E from inner surface and Eb to be the E from the outer surface.

Or, since we're probably in the same class read up on the divergence thm and dielectrics from the book.