Physics Help Forum Electric field in a sphere

 Electricity and Magnetism Electricity and Magnetism Physics Help Forum

 Sep 8th 2010, 02:40 PM #1 Junior Member   Join Date: Aug 2010 Posts: 3 Electric field in a sphere A nonconducting sphere of radius R has a cavity of radius a at its center. The rest of the sphere has a uniform charge density p C/m^3. What is the electric field in the following regions: (a) r > R; (b) a < r < R? (Hint: The charge within a shell of thickness dr is dq = p dV = p4(pi)r^2dr.) I have no idea how to approach this problem. It's asking for the electric field, so I think it has something to do with E = kq^2/r^2 and the problem mentions 4(pi)r^2, which is the surface area of a circle. Please help!
 Sep 8th 2010, 10:35 PM #2 Member   Join Date: Jan 2010 Posts: 48 for r>R, consider as it a point charge and apply the formula you have mentioned.... for a

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