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**1. The problem statement, all variables and given/known data**

A charge q is uniformly distributed over the volume of a solid sphere of radius R. A spherical cavity is cut out of this solid sphere and the material and its charge are discarded. Show that the electric field in the cavity will then be uniform, of magnitude kqd/r^3, where d is the distance between the centers of the spheres.

**2. Relevant equations**

principle of superposition

E=kq/r^2

**3. The attempt at a solution**

I'm not really sure where to start with this one. I know you can take the electric fields of the two spheres and add them together, but the cavity has no charge enclosed. Maybe I'm just reading the problem incorrectly. A push in the right direction would be terrific.

Thanks.