Question

The electric potential at the surface of a shell of radius 10 cm is 120 V. Find the potential at its centre, at r = 5 cm from centre and at r = 15 cm from centre. 

(1) 0 V, 0 V, 80 V 

(2) 120 V, 120 V, 80 V 

(3) 120 V, 0 V, 80 V 

(4) 80 V, 0 V, 120 V

Answer 1

Correct option is: (2) 120 V, 120 V, 80 V 

\(V_{\text{inside}} = V_{\text{surface}}\)

\(\Rightarrow V_{\text{centre}} = V( r =5 \ cm) = 120\ V\)

\(V_{\text{outside}} = \frac{(V_{\text{surface}}) (R) }{r}\)

\(\Rightarrow V(r = 15 \ cm) = \frac{(120\ V)(10 \ cm)}{15\ cm} = 80 \ V\)