Q. A solid metallic sphere has a charge $+ 3Q.$ Concentric with this sphere is a conducting spherical shell having charge $- Q.$ The radius of the sphere is $a$ and that of the spherical shell is $b(b > a).$ What is the electric field at a distance $R(a < R < b)$ from the centre
A) $\frac{Q}{2\pi\varepsilon_{0}R}$
B) $\frac{3Q}{2\pi\varepsilon_{0}R}$
C) $\frac{3Q}{4\pi\varepsilon_{0}R^{2}}$
D) $\frac{4Q}{4\pi\varepsilon_{0}R^{2}}$
Explanation
(c) Electric field at a distance $R$ is only due to sphere because electric field due to shell inside it is always zero
Hence electric field $= \frac{1}{4\pi\varepsilon_{0}}.\frac{3Q}{R^{2}}$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.