A solid spherical conductor of radius R has a spherical cavity of radius a(a<R) at its centre. The chargew at the inner surface, outer an the position r(a<r<R) are ?

Dear Student,

If we put a charge Q in the cavity, It will induce a -Q charge on the inner surface and a Q charge on the outer surface.

Thus surface charge density
$Inner:{\sigma }_{inner}: \frac{Q}{4\pi {\epsilon }_0{a}^2} Outer: {\sigma }_{outer}=\frac{Q}{4\pi {\epsilon }_0{R}^2}$
Regards.