Gauss's Law and electric field magnitude

[amb0027]

Homework Statement

You have a solid, non-conducting cylinder of radius a, length L, and a total charge of Q.
Concentric with this is an uncharged conducting cylindrical shell of inner radius b and outer radius c. Find the magnitude of the electric field for values of r where r < a

Homework Equations

Flux e = integral of E * ds = Qenc / Epsilon not

The Attempt at a Solution

The answer is 2kQr/La^2. I don't understand at all where you get the r, or the a^2. Can anyone break this down for me?

 

[tiny-tim]

welcome to pf!

hi amb0027! welcome to pf!

(have an epsilon: ε and try using the X² and X₂ icons just above the Reply box )

The answer is 2kQr/La^2. I don't understand at all where you get the r, or the a^2. Can anyone break this down for me?

hint: what is the amount of charge inside radius r ?

 

[amb0027]

I don't understand how to approach the problem youre asking either.. I need someone to explain it

 

[tiny-tim]

I don't understand how to approach the problem youre asking either.. I need someone to explain it

You have a solid, non-conducting cylinder of radius a, length L, and a total charge of Q.

i think they mean that the charge is uniformly distributed throughout the sphere …

so what is the amount of charge inside radius r ? ​