Torque on a current loop about a hinge line

1. Nov 20, 2009

theowne

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

A rectangular 20 turn loop that is 12 by 5 cm carries a current of 0.10A. It's hinged at one of the longer 12cm sides. It's mounted with its plane at an angle of 33 degrees to the direction of a magnetic field of 0.50T. What's the torque about the hinge line?

2. Relevant equations

T = iAbsin(theta)

3. The attempt at a solution

I guess my question is about the significance on the hinge line. The example in my book hinges on the z axis located in the middle of loop, so it uses the formula:

t = 2iaB (b/2) sin (theta)
where b/2 sin(theta) is decribed as the "moment arm". When it is hinged on the left longer side instead of the z axis, does this mean the equation would become 2iaB b sin (theta) instead?

2. Nov 20, 2009

tiny-tim

Hi theowne !

(have a theta: θ )
There's various ways of looking a this (including actually working it out from scratch ), but the easiest is probably to add a second loop next to the first, making one big loop with a hinge in the middle!