An insulating spherical shell with inner radius 25.0 cm and outer radius 60.0 cm carries a charge of 150.0 ?C uniformly distributed over its outer surface. Point a is at the center of the shell, point b is on the inner surface, and point c is on the outer surface. (a) what will a voltmeter read if it is connected between the following points: (i) a and b; (ii) b and c; (iii) c and infinity; (iv) a and c?
(b) Which is at higher potential: (i) a or b; (ii) b or c; (iii) a or c?
(c) Which, if any, of the answers would change sign if the charge were -150 ?C?