1. The problem statement, all variables and given/known data Let ρ(r)= Qr/πR4 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 r1 from the centre of the sphere, the magnitude of electric field is ? A) 0 B) Q/4πε°(r1)2 C) Q(r1)2/4πε°R4 D) Q(r1)2/3πε°R4 2. Relevant equations 3. The attempt at a solution Constructing a spherical gaussien surface on which point P lies, Φ= EΔs=q/ε° E4π(r1)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.