A uniformly charged spherical shell with surface charge density [tex]\sigma[/tex] contains a circular hole in its surface. the radius of the hole is small compared with the radius of the sphere. what is the electric field at the center of the hole? I only know this question requires superposition of the sphere and the circle but how do we do it? I thought we can only find the e-field at some point due to a charge? Are we suppose to consider infinitesimal charge on the sphere and do a integration over the entire surface to find the e-field on the cavity? Also, does the size of the hole affect the answer?