A force is exerted on a conductor if it is carrying current and is placed in a magnetic field. Fig. 1.44 shows the direction of the force when a current I flows through the conductor in the direction shown.The force F on the conductor is as follows.
F = BIl (1.480)
where B = flux density
l = length of conductor being linked by flux I = current in conductor
Torque T may be produced electromagnetically if current-carrying conductors are arranged such that they may pivot on an axis that is centered in a magnetic field, as shown in Fig. 1.45.
FIGURE 1.44 Force on a conductor.
FIGURE 1.45 Electromagnetic torque.
The flux in the gap between the magnetic north and south poles will interact with the flux produced by the current in the conductors. If the current is in the direction indicated in Fig. 1.45, the conductors will tend to rotate in the direction shown.
The following equation is used to determine the torque produced.
The bottom drawing in Fig. 1.45 shows the resting position of the conductors. If the direction of the current is switched as the conductors reach this position, the conductors will continue to rotate on the axis in the same direction. Commutation is the process of switching the directions of the currents to allow for continuous rotation.
In motors, the conductors are contained by magnetic steel teeth. The motor field sets up flux through these teeth. The current in the conductors causes the field to distort, setting up a net torque. The steel increases the amount of flux available to produce torque by lowering the circuit reluctance.
An electric motor is a device for converting electrical power to mechanical power (usually rotational).