# Magnetism: torque

A circular loop of wire of radius .5m is in a iniform magnetic field of .30T. the current in the loop is 2A. what is the magnetic torque when the plane of the loop is parallel to the magnetic field?

Ok i first misread this and assued that it meant parallel or sin(90 degrees) which equals 0.

I have thus far...
A = PI * r^2 = PI * .5^2 = .785 now plug thast into this formula.
t = NIAB = (?)(2)(.785)(.3). I know that to get the number of turns is number of loops divided by length. But there is no such animal, I have a feeling that I am using the wrong formula perhaps or have done something incorrect. Ive tripled check and still get .471 as my answer. What am I doing wrong?
dx ## Answers and Replies

Homework Helper
"Ok i first misread this and assued that it meant parallel or sin(90 degrees) which equals 0."

Actually, sin(90)= 1, not 0. Did you mean cos?

You are told that the loop is parallel to the exterior magnetic field. That means that the loop's magnetic field (which is perpendicular to the plane of the loop) is perpendicular to the exterior magnetic field.

" I know that to get the number of turns is number of loops divided by length"

I don't understand this- the number of turns IS the number of loops. Do you mean "loops per unit length"?

Originally posted by HallsofIvy
"Ok i first misread this and assued that it meant parallel or sin(90 degrees) which equals 0."

Actually, sin(90)= 1, not 0. Did you mean cos?

You are told that the loop is parallel to the exterior magnetic field. That means that the loop's magnetic field (which is perpendicular to the plane of the loop) is perpendicular to the exterior magnetic field.

" I know that to get the number of turns is number of loops divided by length"

I don't understand this- the number of turns IS the number of loops. Do you mean "loops per unit length"?

"Actually, sin(90)= 1, not 0. Did you mean cos?"

I already knew that but thought I read somewhere in the book about it. Ill double check cuase your correct.

" I know that to get the number of turns is number of loops divided by length"

Yes!

What am I doing wrong Ivy? I need help, plz?
Dx teddy
A circular loop of wire of radius .5m is in a iniform magnetic field of .30T.

a circular LOOP means that the no of turns=1.

this gives the answer 0.471 N so i think your answer is correct.
Does the book gives different answer?

Originally posted by teddy
a circular LOOP means that the no of turns=1.

this gives the answer 0.471 N so i think your answer is correct.
Does the book gives different answer?

No! This question is one of those w/o the answer in the back of the book. I am going to ask again in class tomorrow, I do also beilive its correct. Thanks!
Dx 