What is the magnitude of the torque acting on the loop? T = IAB

[mr_coffee]

A circular wire loop of radius 20.0 cm carries a current of 3.10 A. It is placed so that the normal to its plane makes an angle of 34.0° with a uniform magnetic field of 15.0 T.

I don't understand why this isn't right, i got the first part right, it wanted me to find the magnetic dipole moment of the loop, which i found to be .3896 Am^2; I got this by using M = IA;
now it wants me to find the magnitude of the torque acting on the loop. So I used the formula:
Torque = IAB;
I = current
A = area of loop
B = Magnetic field;
Torque = (3.10)(PI*.20^2)(15) = 5.84 Nm, which is wrong, any ideas why?
Thanks.

 

[James R]

The torque is only IAB if the field lines are perpendicular to the plane of the loop, whioch isn't the case here.

The complete formula is:

\tau = IAB \sin \theta

where \theta is the angle between the normal to the loop and the magnetic field. In your problem, the relevant angle is 34 degrees.

In vector terms, the torque is:

\vec{\tau} = \vec{\mu} \times \vec{B}

where \vec{\mu} is the magnetic moment.

 

[mr_coffee]

ohh thanks a lot james, worked great!