A solid sphere of radius R has a charge Q distributed in its volume with a charge density `rho = k r^a`, where k and a are constants and r is the distance from its centre. If the electric field at `r = R/2` is `1/8`. times that at `r = R,` find the value of a
Options:
(a) 2
(b) 3
(c) 5
(d) 6