Q. Current-carrying conductors?

Current-carrying conductors, when placed in magnetic fields, experience mechanical force. Considering only the effect of the magnetic field, the Lorentz force equation gives the force F as

F = BlI

when a current-carrying conductor of length l is located in a uniform magnetic field of flux density B, and the direction of the current in the conductor is perpendicular to the direction of the magnetic field. The direction of the force is orthogonal (perpendicular) to the directions of both the current-carrying conductor and the magnetic field. Equation is often used in electric machine analysis.

The principle of interaction is illustrated in Figure, in which ¯B is the flux density, ¯I the current, and ¯F the force. Shown in Figure (a) is the flux density ¯B of an undisturbed uniformfield, on which an additional field is imposed due to the introduction of a current-carrying conductor. For the case in which the current is directed into and perpendicular to the plane of the paper, the resultant flux distribution is depicted in Figure (b). It can be seen that in the neighborhood of the conductor the resultant flux density is greater than B on one side and less than B on the other side. The direction of the mechanical force developed is such that it tends to restore the field to its original undisturbed and uniform configuration. Figure (c) shows the conditions corresponding to the current being in the opposite direction to that of Figure (b).

The force is always in such a direction that the energy stored in the magnetic field is minimized. Figure shows a one-turn coil in a magnetic field and illustrates how torque is produced by forces caused by the interaction between current-carrying conductors and magnetic fields.