# Homework Help: Electromagnetics = Biot-Savart Law around square path

1. Apr 15, 2010

### satchmo05

1. The problem statement, all variables and given/known data
Find the B-field at the center of the square loop located above the xy plane, with width (w), and current I rotating counter-clockwise.

2. Relevant equations
Here is the given equation:
B = [(μo*I*aФ)/(4∏*ρ)](cosα2 – cosα1)

B = [(4μo*I)/(∏*w*(√2))]az
How do I obtain this answer? I am having trouble with the angles that I am supposed to use.
3. The attempt at a solution
I used (w/2) for the radial component, ρ. I used 45 degrees for α2, and 90 degrees for cosα1, and this is obviously wrong. Which angles do I use to get the correct angle?

Last edited: Apr 15, 2010
2. Apr 15, 2010

### satchmo05

Solving this analytically for cosα2 - cosa1, I should receive 2/sqrt(2). How should I set up my angles to acheive this? Thank you for all help, I greatly appreciate it!

3. Apr 15, 2010

### kuruman

What kind of picture goes with the given equation? In other words, for what situation was it derived? How are ρ, α1 and α2 defined?