Finding Torque on current loop.

[Covenant32]

Homework Statement

The current loop is in the y-z plane. The direction of the magnetic field is in the z-direction.

A) Which way is the torque on the current loop?
B) If the current is 4 amps and the magnetic field strength is 2.5 Tesla, what is the magnitude of the torque?

here is the picture (which I drew): http://twitpic.com/7e0zv9

Homework Equations

Right Hand Rule 2

T=IAB, T=NIABsinθ. The torque formulas I have necessitate finding an area of the current loop. But, as you can see from the picture (which displays all info. given) there is no way to find the area.

The Attempt at a Solution

A) Well, the loop is parallel to the field. If I use the right hand rule 2, the direction of the torque would be into the page, would it not?

B) I feel that I am missing something crucial. I have done a few problems similar to this one, but I was always given some number to work with to find the area of the current loop.

Seriously, ANY help is very much appreciated. Thank you.

 

[Delphi51]

In high school physics, we use F = I*L*B (component of B perpendicular to I).
You could use that the calculate the force on the two sides of the loop that are perpendicular to the B field. If you knew their length. A larger loop would feel a larger force and greater torque than a smaller one. So, same conclusion, the size of the loop is necessary to find the answer.

 

[Covenant32]

In high school physics, we use F = I*L*B (component of B perpendicular to I).
You could use that the calculate the force on the two sides of the loop that are perpendicular to the B field. If you knew their length. A larger loop would feel a larger force and greater torque than a smaller one. So, same conclusion, the size of the loop is necessary to find the answer.

Thank you, Delphi. I think that perhaps the torque is zero. My reasoning is that the forces acting on the loop are not trying to rotate it. At least that is how it appears.


What do you think of that?

 

[Delphi51]

No, it is exactly like the loop of wire in an electric motor. The forces are opposite in the top and bottom wires because the current is reversed, so you do have torque about the center of the loop.

 

[asteriatic]

I would like to first clarify that the torque on a current loop is defined as the cross product of the magnetic moment of the loop and the magnetic field. The magnetic moment is given by the product of the current and the area enclosed by the loop.

Now, to answer your questions:

A) Based on the given information, the direction of the torque on the current loop would indeed be into the page, as determined by the right hand rule 2.

B) As you mentioned, in order to calculate the torque on the loop, we need to know the area enclosed by the loop. Without this information, it is not possible to calculate the torque. Therefore, the magnitude of the torque cannot be determined with the given information.

In order to solve this problem, you would need to know either the dimensions of the loop or the angle between the magnetic field and the plane of the loop. Once you have this information, you can use the formula T=NIABsinθ to calculate the torque.

I hope this helps clarify the situation. If you have any further questions, do not hesitate to ask.