# Homework Help: Electric field

1. Apr 21, 2012

### Rider4

1. The problem statement, all variables and given/known data
A uniformly charged wire or radius R1=0.02m runs down the axis of a cylinder of inner radius R2=0.06m. The potential difference between the wire and cylinder is 60 volts. Find the electric field at the surface of the wire.

2. Relevant equations
Electric flux=Q/$\epsilon0$
Electric flux=integral of E dA
V=integral of E dr

3. The attempt at a solution
Q/$\epsilon0$=E(2pi)(r)(L)
Applying the above equations, I got E=(Q/$\epsilon0$)(1/((2pi)(r)(L))
I then integrated as a function of r, and got V=(Q/$\epsilon0$)(1/((2pi)(L))(ln(r2/r1))
I'm not too sure where to go from here, so any help would be greatly appreciated.

2. Apr 21, 2012

### rude man

Solve for Q.
Then think Gauss.

Last edited: Apr 21, 2012
3. Apr 21, 2012

### Rider4

I solved for Q and got Q=(3.29$\ast$10^8)/L
then should I plug Q back in for the Q in the equation E=(Q/ϵ0)(1/((2pi)(r)(L))

4. Apr 21, 2012

### rude man

Yes, with of course the appropriate vaue for r.

BTW I'm not checking your math, just your reasoning. Hope you understand the steps you took well.