A sphere of radius R has a uniform distribution of electric charge in its volume. At a distance x from its centre, for x < R , the electric field is directly proportional to
x
Let sphere has uniform charge density ρ(=3Q4πR3) and E is the electric field at distance X from
the centre of the sphere.
Applying Gauss law
E.4π x2=qϵ0=ρV′ϵ0=ρϵ0×43πx3
(v'= Volume of dotted sphere)
∴E=ρ3ϵ0x⇒E∝x