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sonofabitch, need math/physics HELP!!! (magnetism)

B

beer

Lifer
OK

basic biot-savart law question.

I have a current-carrying square, side length L and current I.

The magnetic field magnitude is 4*(4(pi)*10^-7*I)/(4(pi)*(L/2))*(cos(theta1)-cos(theta2)) where theta1 and theta2 are the angles along the axis of the side. I'm going to skip the derivation for that, obviously, but its the same for any line. This is correct.

However, I bend the square into a circular loop.

The magnitude of a circle carrying a current is: (4(pi)*10^-7*I))/(2*R) because you are integrating over 2*pi for the loop. The question is, how do you get the radius from the side L of the square? NO ONE has a clue how to do it on our own physics forums, maybe someone here can help? I set R = sqrt(L^2/pi) but that isn't working, and I'm pretty sure this formula is correct.

 
What are you trying to calculate? The magnetic field along the central axis (going through the center of the circle but perpendicular to the plane of the circle) of the wire?

EDIT: Well anyway, if that's the case, they have the solution here: http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/curloo.html#c3

I know I have the proof somewhere in my physics notes, but I'm not sure where those are right now (I took the class last spring). LMK if you really need it and I'll find it.
 
The magnitude of the magnetic field at the center of the current-carrying circular loop.

Edit: Yes it will be perpendicular. The magnitude of dS x r will be just dS = Rd(theta) in the direction of -k
 
The perimeter of the original square should be 4L. If you've taken that square and wrestled it into a circle, then shouldn't the circumference of that circle also be 4L? If so, then R=2L/pi. Maybe I'm misunderstanding your question...
 
Originally posted by: PowerEngineer
The perimeter of the original square should be 4L. If you've taken that square and wrestled it into a circle, then shouldn't the circumference of that circle also be 4L? If so, then R=2L/pi. Maybe I'm misunderstanding your question...
Click to expand...


fsck
I was doing area and not circumference.

That worked. Sweet.

 
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