Electromagnetism: Turning effect of coil

[lingling]

Homework Statement

This is a question about turning effect on a current-carrying coil lying between the poles of a magnet.
Please refer to the following link:
http://img11.picsplace.to/img.php?file=img10/22/N1_000.gif
On the textbook, it is stated the turning effect on the coil can be increased by increasing the area of the coil (inside the magetic field).
I understand the force would increase if AB and CD increases.
But I'm not sure whether the turning effect will increase when BC increases.
Can anyone tell me?

Thank in advance.

Homework Equations

The Attempt at a Solution

 

[dobry_den]

The force acting on a current-carrying conductor could be calculated with the following formula:

F = BIl\sin\alpha

where B is magnetic induction, I is current, l is length of the conductor and <alpha> is the angle between the conductor and the magnetic field (the vector B). The angle between the conductor BC and the magnetic field is 0<pi> - the answer is thus apparent.