Mechanical Systems 353
where:
F = force acting on a conductor in newtons,
B = flux density in teslas,
l = length of the conductor in meters, and
I = current through the coil in amperes.
Given: a conductor 1.8 meters long has a current flow of 50 A through
it. It is contained within a magnetic field of 0.25 tesla density.
Find: the maximum Lorentz force acting on the conductor.
Solution:F = B × 1 × l
= 0.25 × 1.8 × 50
F = 22.5 newtonsThe rotating effect produced by the interaction of two magnetic fields
is called torque or motor action. The torque produced by a motor depends
on the strength of the main magnetic field and the amount of current flow-
ing through the conductors. As the magnetic field strength or the current
through the conductors increases, the amount of torque or rotary motion
will increase also.DC MOTORS
Motors that operate from DC power sources are often used in in-
dustry when speed control is desirable. DC motors are almost identical in
construction to DC generators. They are also classified in a similar man-
ner as series, shunt, or compound machines, depending on the method of
connecting the armature and field windings. The permanent-magnet DC
motor is another type of motor that is used for certain applications.DC Motor Characteristics
The general operational characteristics common to all DC motors are
shown in Figure 14-3. Most electric motors exhibit characteristics similar
to those shown in the block diagram. In order to discuss DC motor char-
acteristics, you should be familiar with the terms load, speed, counterelectro-
motive force (cemf), armature current, and que. tor The amount of mechanical
load applied to the shaft of a motor determines its operational character-
istics. As the mechanical load is increased, the speed of a motor tends to