Problems regarding 2 conducting cylinders

[Donnyboy]

Homework Statement

Based on the picture, the inner cylinder has a radius R1 and the outer R2, σa=-σ ; σb=3σ

each cylinders are of lengths greater than R1, ignore the end effects and neglect thickness of cylinder.

a). What is the electric potential difference between the outer cylinder and the inner cylinder

b). What is the magnitude of the electric field outside the cylinders , r>R2

c). What is the electric potential difference between a point at distance r=2R2 from the symmetry axis and the outer cylinder ?

**all answers are to be expressed in terms of r,R1,R2,σ and ε0 wherever relevant

Homework Equations

Gauss Law (is it?)

The Attempt at a Solution

i tried selecting a gaussian surface between the 2 cylinders for question a, in which should yield

E= σa/(π*ε0 *(R1)^2) aaaand i got stuck :/ this is due in 24 hours and i am in desperate need of assistance

for b). is the magnitude of the E field 0 ?

 

[Asim Riaz]

because i have the same charge on the inside and out side of the cylinderfor c). again i tried selecting a gaussian surface but this time between 2r2 and the outer cylinder, which yielded E= σb/(π*ε0 *(R2)^2) again, i'm stuck.