The region between two concentric spheres of radii ‘a’ and ‘b’, respectively (see figure), has volume charge density $\rho = \frac{A}{r}$ , where A is a constant and r is the distance from the centre. At the centre of the spheres is a point charge Q. The value of A such that the electric field in the region between the spheres will be constant, is : <br>

Question

( A ) $\frac{2Q}{\pi a^2}$
( B ) $\frac{Q}{2 \pi a^2}$
( C ) $\frac{2Q}{ \pi (a^2-b^2)}$
( D ) $\frac{Q}{2 \pi (b^2-a^2)}$