- #1

- 123

- 5

## Homework Statement

Let ρ(r)= Qr/πR

^{4}be the charge density distribution for a solid sphere of radius R and total charge Q.For a point 'P' inside the sphere at distance r

_{1}from the centre of the sphere, the magnitude of electric field is ?

A) 0

B) Q/4πε

_{°}(r

_{1})

^{2}

C) Q(r

_{1})

^{2}/4πε

_{°}R

^{4}

D) Q(r

_{1})

^{2}/3πε

_{°}R

^{4}

## Homework Equations

## The Attempt at a Solution

Constructing a spherical gaussien surface on which point P lies,

Φ= EΔs=q/ε

_{°}

E4π(r

_{1})

^{2}= q/ε

_{°}

where q is the charge enclosed by the gaussien surface.

I'm having trouble as I don't know how to find q. I know dq= ρdv and so q=∫ ρdV , but if I do substitute ρ in that integral , I don't know what to do with the dV.

Please give me a hint as to how to proceed.