# Magnetic field problem

1. Apr 10, 2006

### Punchlinegirl

An infinite sheet of current, perpendicular to the y axis is located at y=0. The linear current density $$\lambda_+_x$$ flows in the +x direction. By inspection, we expect the magnetic field direction B_y, on the positive y side of the sheet to be in the +z direction while the magnetic field on the negative y side of the sheet to be in the -z direction. We choose the Amperican loop as the dashed line with sides of length L and w. The magneto motive force is given by 2LB and the current enclosed is $$\lambda_+_x * L$$.
Let L=0.5 m, w=0.078 m, $$\lambda_+_x$$= 1.89 A/m. Find the magnitude of the magnetic field B. Answer in units of T.

I really have no idea how to do this problem. Can someone help? Thanks

2. Apr 10, 2006

### siddharth

Hint: Ampere's Law.
Read the question again. Towards the end of the question, there is a big hint given on what closed loop to take.

3. Apr 11, 2006

### Punchlinegirl

Ok so the loop I use has sides L and W.
I know that Ampere's Law says B*ds*cos theta= $$\mu$$*I
So to get B I divide $$\mu$$ *I by 2L+2W since you use the perimeter of the square.
So its (1.25e-6)(0.5)(1.89)/ (2*0.5)+(2*.078)