A metallic spherical shell has an inner radius R1 and outer radius R2. A charge Q is placed at the centre of the spherical cavity. What will be surface charge density on:

(i) the inner surface

(ii) the outer surface?

Hint: Use the concept of induction of charge.
Step 1: Find the charge induced on the inner and outer surfaces.
Here, the charge placed at the centre of the spherical cavity is positively charged. So, the charge created at the inner surface of the sphere, due to induction will be -Q and due to this charge created at the outer surface of the sphere is +Q.
Now, the surface charge density on the inner surface =-Q4πR12, and,
Surface charge density on the outer surface =+Q4πR22