A spherical conducting shell of inner radius r1 and outer radius r2 has a charge Q.
(a) Show that the field inside the cavity is zero.
(b) A charge q is placed at the centre of the shell. What is the surface charge density on the inner and outer surfaces of the shell?
(c) Is the electric field inside a cavity (with no charge) zero, even if the shell is not spherical; but has any irregular shape? Explain.
(a) It is know that the entire charge Q resides on the outer surface of the shell. i.e. no charge resides in the cavity.
(c) When the shell is not spherical and has any irregular shape, the charge inside continues to be zero as charge would always reside on the outer surface of the shell. Therefore, electric field inside cavity will remain zero.