First time poster here! EDIT: SOLVED!!(adsbygoogle = window.adsbygoogle || []).push({});

Thanks, I figured out from the related links at the bottom of the page. >_>b

1. The problem statement, all variables and given/known data

Find the electric field inside a sphere which carries a charge density proportional

to the distance from the origin, [tex]\rho[/tex] = kr, for some constant k.

2. Relevant equations

[tex]\oint E.da[/tex]

[tex]a = 4 \pi r^2/3[/tex]

[tex]da = 4 \pi r^2[/tex]

[tex]\rho = kr[/tex]

[tex]E = q/(r^2 4 \pi \epsilon _0)[/tex]

Where q = charge inside

3. The attempt at a solution

[tex]\oint E \bullet da = \int q/(r^2 4 \pi \epsilon _0) \bullet 4 \pi r^2[/tex]

The 4 pi r^2 terms cancel, leaving on the right

[tex]q/ \epsilon_0[/tex]

Substitute rho into the eqn. as to integrate all dimensions of the sphere

[tex] \int \rho d \tau / \epsilon_0[/tex]

Here's where I get stuck, I know that

[tex] \rho = kr [/tex]

What do I do with [tex]d \tau[/tex]? I'd imagine that it'd be easiest to do in spherical coordinates, so do I just add dr, dtheta, drho?

Also... How do I put a dot into this LaTex thing?

Thank you!

**Physics Forums | Science Articles, Homework Help, Discussion**

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Homework Help: Finding E field inside a sphere with charge proportional to radius

**Physics Forums | Science Articles, Homework Help, Discussion**