Question

A slender, 400- g bar magnet 10.0 cm long has a magnetic moment of 5.60 A m2. It is held at an angle of 45 o to the direction of a uniform magnetic field. When released, it begins to rotate about its center with an initial angular acceleration of 5.35e3 rad/s2. What is the magnitude of the magnetic field?

Answer 1

The magnetic field B exerts a torque ? on a magnetic dipole, which has a magnetic moment M. This torque produces an angular acceleration ? on the bar about its center, which is determined by its moment of inertia I.

Equations and Calculations:

The torque ? exerted by a magnetic field B on a magnetic dipole having magnetic moment M is given by [see Source 2]:

(1) ? = M X B

= M * B * sin (?),

where:
? = the angle between the magnetic moment (aligned with the bar axis) and B = 45