A solid metal sphere of radius $$R$$ having charge $$q$$ is enclosed inside the concentric spherical shell of inner radius $$a$$ and outer radius $$b$$ as shown in the figure. The approximate variation electric field $$\vec{E}$$, as a function of distance $$r$$, from centre $$O$$, is given by:

The electric field inside conducting materials is zero in electrostatic equilibrium, and outside a spherically symmetric charge distribution, it follows Gauss's Law: $$E = \frac{k q}{r^2}$$.

For $$0 \le r < R$$ (inside solid metal sphere):   $$E = 0$$

For $$R \le r < a$$ (space between sphere and shell):     $$E = \frac{1}{4\pi\varepsilon_0}\frac{q}{r^2}$$

For $$a \le r \le b$$ (inside the conducting spherical shell):    $$E = 0$$

For $$r > b$$ (outside the entire system):   $$E = \frac{1}{4\pi\varepsilon_0}\frac{q}{r^2}$$