At a point `20 cm` from the centre of a uniformly charged dielectric sphere of radius `10 cm`, the electric field is `100 V//m`. The electric field at `3 cm` from the centre of the sphere will be

Options

A. 150 V/m
B. 125 V/m
C. 120 V/m
D. Zero

Answer

C

Explanation

R = 10 cm, r = 20cm , E = 100V /m
`E_("(outside)")=(KQ)/(r^2)implies 100 = (9xx10^9xxQ)/((0.2)^2)`
`implies Q = (400 xx10^(-2))/(9xx10^9) = 4/9 xx10^(-9)C`
`E_("(inside)")=(KQr)/(R^3)= (9xx10^9 xx4 xx10^(-9)xx0.03)/(9xx(0.1)^3) = 120V //m.`