A point charge +Q is placed at point p inside a thin metallic spherical shell with its centre at c as shown in the figure. A and B  are two points outside the shell at same radial distance from c. Electric fields at A and B are ${\mathrm{E}}_1\mathrm{and}{\mathrm{E}}_2$ respectively. Then

Electric lines of force emerging from +Q terminate at the linear surface of the shell and points A and B are completely screened from the charge +Q lying inside the shell. Hence, the electric field at two points is only due to charge lying on the surface of shell which is equal in both cases so ${\mathrm{E}}_1={\mathrm{E}}_2$