# Homework Help: Solving for dA in Gauss's Law

1. Sep 20, 2007

### Rib5

Hey, I'm having some trouble solving for the dA portion of Guss's Law for a sphere as the Gaussian surface and a point charge on the inside.

According to my book, Integral(1dA) = 4(pi)r^2

So when I try to integrate it myself I get 2(pi^2)r^2
The integral I solve is $$\int$$$$\int r\phi r\theta$$ where theta = [0,2pi] and phi = [0,pi]

Can anyone set me straight please?

Last edited: Sep 20, 2007
2. Sep 20, 2007

### Staff: Mentor

On the surface of a sphere, the element of area bounded by $d\theta$ and $d\phi$ has area $(r d\theta)(r \sin \theta d\phi) = r^2 \sin \theta d\theta d\phi$.