# Question: consider an infinitely long cylinder of radius r with two...

###### Question details

Consider an infinitely long cylinder of radius R with two
spherical cavities, also of radius R. The cylinder carries a
uniform volume charge density of ρ. There are two point charges at
the center of the spherical cavities both of charge q.

Hint: Just as the previous hint, superposition is your friend. A
suggestion is to find the contributions from the cylinder and
spheres separately.

(a) Find the electric field at the points A, B, and C in the
diagram below.

(b) Suppose that the point charges have a magnitude q = 4πR3ρ. Find
the energy density of the field outside the cylinder.