1. The problem statement, all variables and given/known data I'm having a bit of trouble with this problem: "A spherical ball of charge has radius R and total charge Q. The electric field strength inside the ball (r≤R) is E(r)=r^4Emax/R^4. a. What is Emax in terms of Q and R? b. Find an expression for the volume charge density ρ(r) inside the ball as a function of r." 2. Relevant equations Φ=EA Φ=Q/ε0 Q=ρV E(r)=r^4Emax/R^4 3. The attempt at a solution I found the answer for part (a.) with no trouble: Emax=Q/(4πR^2ε0) However, part (b) has proved to be a lot harder. Here is my attempt: Since φ=EA and φ=Q/ε0,, I chose to use the original equation for electric field (since I have a correct answer for Emax), multiply it by the surface area of a smaller sphere with radius "r" (inside the original sphere with radius R), and set this equal to Q/ε0 as follows: Q/ε0=(4πr^2)(r^4Emax/R^4) Then, I determined the charge of the small sphere with radius "r" (inside the original sphere with radius R) as follows: ρ=charge density Q=ρV Find charge of small sphere (inside the original sphere with radius R): dQ=ρ4πr^2dr Q=∫ρ4πr^2dr (with the limits of the integral being 0 to r) Q=(4/3)πr^3ρ Then I used the equation I found earlier: Q/ε0=(4πr^2)(r^4Emax/R^4) Then I input the values for Emax and Q, and I get the formula for charge density: (4/3)πr^3ρ/ε0=r^4(Q/4πR^2ε0)/R^4 ρ(r)=3r^3Q/4πR^6 I tried entering the value to see if it is correct and the program tells me that I am missing or failing to add a numerical value. I've tried going through it and I can't seem to find the error. If one of you all can help me out I'd be grateful.