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**[SOLVED] Electric field around cylinder**

## Homework Statement

An infinitely long cylinder with r = 4.0 cm has a uniform charge density of 200 nC/m^3. What is the electric field 3.9 cm away from the axis?

## The Attempt at a Solution

The first thing I thought is that the field has got to be 0 since all the charge will be on the surface of the cylinder. But maybe this applies only to spheres?

Anyway, I calculated the charge per meter: 1.01 nC/m. Then I used Gauss law:

Q/l = e

_{0}E*2*pi*r, which yields

E = (Q/l)/(2*pi*r) =

__0.47 kN/C__

Is this correct?