Question

A solid conducting sphere of radius $a$ has a net positive charge $2 Q$. A conducting spherical shell of inner radius $b$ and outer radius $c$ is concentric with the solid sphere and has a net charge $-Q$. The surface charge density on the inner and outer surfaces of the spherical shell will be

• A. $-\frac{2 Q}{4 \pi b^{2}}, \frac{Q}{4 \pi c^{2}}$
• B. $-\frac{Q}{4 \pi b^{2}}, \frac{Q}{4 \pi c^{2}}$
• C. $0, \frac{Q}{4 \pi c^{2}}$
• D. None of the above

Answer 1

Answer: (A)

Surface charge density $(\sigma)=\frac{\text { Charge }}{\text { Surface area }}$

So $\sigma_{\text {inner }}=\frac{-2 Q}{4 \pi b^{2}}$
and $\sigma_{\text {Outer }}=\frac{Q}{4 \pi c^{2}}$