Question

For a charged conducting spherical shell, electric field strength at the inside points is zero and electric potential has a constant value so that the volume is equipotential. Outside the shell, for the purpose of field and potential calculations, the system behaves as if its whole charge were concentrated at its centre so that the expressions that apply to a point charge also apply here. Variation of field strength and potential with r  is as shown in fig. Here r is the distance from centre and R the radius of shell.

Consider an isolated, thin conducting spherical shell 'A' of radius 20cm. The shell is given a charge Q_A that distributes uniformly and the maximum strength of the resulting electric field has a value 11250 N/C. 'B' is another isolated thin conducting spherical shell of radius 40cm. It is given a charge Q_B that distributes uniformly and in this case, maximum strength of the resulting field as a value 4500 N/C. Q_A and Q_B are of same nature. The two shells A and B are now kept in a concentric manner as shown in fig. x is at distance 10cm from the centre.  [Take V = 0 at r = $\infty$]