The region between two concentric spheres of radii ‘a’ and ‘b’, respectively (see figure), has volume charge density 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
Qenc - charge enclosed by closed surface.
Now putting the value of q in equation (i)
E will be constant if it is independent of r
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