Figure shows a charge q placed at the centre of
a hemisphere. A second charge Q is placed at
one of the positions A, B, C and D. In which
position(s) of this second charge, the flux of the
electric field through the hemisphere remains unchanged?
(a) A (b) B
(c) D (d) None of these
Answers
Flux in the above case has a lot of dependence on incoming and outgoing lines of force at the surface being considered. If there is a way for the incoming lines of force to go out then there will be presence of both the lines of force otherwise not. If both the lines are present then, the flux through that point will not change while at others it will. Seeing the figure above we can only say that for flux due to charges at point B and D will be limited only by the incoming lines of force there will be no outgoing lines of force so the flux will change. While at points A and C the lines of force have a way to go out hence both the incoming lines of force and the outgoing lines of force are present.
Thus, the flux will not change through the point A and C both due to the above mentioned reasons.