Question

How might you measure the magnetic dipole moment of a compass needle? Discuss.

Answer 1

If you can measure the magnetic field intensity and the torque it exerts on the needle then the equation
\[\tau=mB\] can be used (in this situation make sure the field is orthogonal to the needle). If you can't measure the torque directly you can always just measure the radius of the needle and the tangential acceleration and use the equation
\[\tau =(I/r)a _{tangential}\] where I is the moment of inertia (which I would think can be approximated by that of a thin rod).