# The region between two concentric spheres of radii ‘a’ and ‘b’,respectively

The region between two concentric spheres of radii *‘a’ *and *‘**b**‘**,*respectively (see figure),has volume charge density *P *= 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 :

- Q/2πa²
- Q/2π(b² – a²)
- 2 Q/π(a² – b²)
- 2Q/π a²