# Homework Help: Cylindrical Capacitors Questions

1. Mar 8, 2010

### apphysicsgirl

1. The problem statement, all variables and given/known data
An isolated cylindrical capacitor consists of two concentric conducting cylinders of length L and radii a and b. The inner and outer conductors carry +Q and -Q, respectively.
a. Determine the electric field between the conductors.
b. Determine the electric potential difference between the two conductors.
c. What is the capacitance of this device?

2. Relevant equations
V=$$\int$$E dL
$$\oint$$E dA=Q/Epsilon
C=Q/V

3. The attempt at a solution
a. I got as my answer E=Q/(2$$\pi$$Epsilon not (aL))
b. I used the integral with V and got Q/(2$$\pi$$Epsilon not (a) (ln(b/a))
c. I plugged my answer from b into C=Q/V and got ln(b/a)/(2$$\pi$$Epsilon not (a))

I am not sure if I did any of these right...

2. Mar 8, 2010

### ehild

Is the electric field independent of position?

ehild