# Math Help - From PHF

1. ## From PHF

I'm helping someone in PHF but as Latex is down there, I'm posting here only for the latex. I might use this thread if the OP needs more explanations on the same problem.
So Biot-Savart's law is $d \vec B =\frac{\mu _0}{4\pi} Id\vec l \times \frac{\vec r}{r^3}$. Thus $\vec B=\frac{\mu _0}{4 \pi} \oint I d\vec l \times \frac{\vec r}{r^3}$. Now go back to PHF.

I'll be using this post for the same problem and other posts for others...

2. Another problem of the same OP:

$V=-\int_{\gamma} \vec E \cdot d\vec l$.

Energy stored within an electric field: $\frac{1}{2} \varepsilon \int_{V} |\vec E|^2 dV$.