Ok i'm realllly unsure about this! If a spherical cavity of radius 3.66cm in a piece of metal (kind of cube, but not a perfect cube) has a charge of +Q at it's centre and there is a point P1 located half way between the spherical cavity and it's surface and a point P2 located in the metal piece , use gauss Law to find the electric field at a) Point P1 b) point P2 a) This is fine for me Let e0 = permittivity of free space epsilon 0 e0 SurfaceIntegral (E dA) = q e0 E (4 pi r^2 ) = q E = kq /r^2 which is coulomb's law derived! and just plug and away i go! b) But for point P2 err can i actually use a spherical surface here?? as in do the same thing as before but use a bigger value for r i.e. radius of sphere + distance of sphere to point P2 appropriate? or not?