Educator

Torque on a Current Carrying Loop

• If the magnetic field B is parallel to the plane of a loop carrying a current I, the torque exerted by B on the loop is IAB, where A is the area of the loop.
• In general, the torque is given by I A x B, where A is a vector whose magnitude is the loop area and which is directed normal to the loop plane.
• The magnetic moment of a loop of area A carrying a current I is the product m = IA and is directed normal to the plane of the loop: if the four fingers of the right hand circle around in the direction of the current, then the thumb points in the direction of m.
• The torque exerted by a magnetic field B on a magnetic moment m is given by the cross product m x B. The potential energy of a magnetic dipole m in a magnetic field B is the dot product –m.B.