Homework Help: Find the charge density inside a solid insulating sphere?

1. Sep 16, 2014

hockey

1. The problem statement, all variables and given/known data
The electric field at a distance of 0.143m from the surface of a solid insulating sphere with radius 0.381m is 1630N/C .

a) Assuming the sphere's charge is uniformly distributed, what is the charge density inside it?

b) Calculate the electric field inside the sphere at a distance of 0.237m from the center.

2. Relevant equations
E1/E2 = r1/r2
E = Cr

3. The attempt at a solution

a) I know that the electric field for part a can be found by using the formula E=Cr, so I can get C = 4278.22 N/(C*m). I know that the charge density is a factor of C, but I do not know the actual formula for it.

b) This should be able to be solved with the ratio E1/E2 = r1/r2, and when I solve for E2 I get a result of 737.2 N/C. This result is not correct, but I am not sure if the problem is in my ratio.

2. Sep 16, 2014

Simon Bridge

You can figure it out though. Hint: what are the units of charge density?

Write out the equation for E1 and E2 separately, then find E1/E2.

3. Sep 17, 2014

rude man

a) 1. figure out what total charge Q is for an E field at the specified location.
2. Q = volumetric charge density x volume gives you charge density.

b) 1. Use Gaussian surface.