# Biot-Savart and a Square Loop

1. Jul 27, 2011

### 012983

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

A conductor in the shape of a square of edge length 0.28 m carries a current I = 17.0A. Calculate the magnitude of the magnetic field at the center of the square. Round your answer to three significant figures. Take the permeability of free space to be 4*pi*10^-7.

2. Relevant equations

L = length of one side of the square = 0.28 m
I = current = 17 A
Sin(theta2) = 45 degrees = sqrt(2)/2
Sin(theta1) = -45 degrees = -sqrt(2)/2

B = 4{[(mu*I)/(4*pi*L)] * (sin(theta2) - sin(theta1))}

3. The attempt at a solution

I think I've got it, but the website won't take my answer. Sorry for the lack of LaTex.

Values for theta were obtained by forming two 45-45-90 triangles; those values are the distance from any side to the center.

Plugging everything in, I get 4{[(4piE-7*17) / (4*pi*0.28)] * sqrt(2)} = 34.3 * 10^-6 T. However, this is incorrect. Have I made a calculation error? A concept error? This will be my 23rd try putting something into the website and I am tired of it.

Thanks for any help.

2. Jul 27, 2011

### tiny-tim

hi 012983!

i can't work out what formula you're using for the Biot-Savart law

the angle should be the angle between the field and the plane of the loop (90°)

and shouldn't there be an r2 somewhere?

see http://en.wikipedia.org/wiki/Biot-Savart_law" [Broken]​

Last edited by a moderator: May 5, 2017
3. Jul 28, 2011