Question

A metallic spherical shell has an inner radius `R_(1)` and outer radius `R_(2)`. A charge is placed at the centre of the spherical cavity. The surface charge density on the inner surface is

A. `q/(4piR_(1)^(2))`
B. `(-q)/(4piR_(1)^(2))`
C. `(q^(2))/(4piR_(2)^(2))`
D. `(q)/(4piR_(2)^(2))`

Answer 1

Correct Answer - B
When a charge +q is placed at the centre of spherical cavity as shown in figure.
Charge induced on the inner surface of shell = -q" "… (i)
Charge induced on the outer surface of shell = +q" "… (ii)
`therefore` Surface charge density on the inner surface = `(-q)/(4piepsilon_(0)R_(1)^(2))`