PASCO SE-8657 MOTOR ACCESSORY - Manual (Page 17)

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012-06247A Motor Accessory
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EQUIPMENT NEEDED OPTIONAL EQUIPMENT
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Motor Accessory
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Voltage Sensor
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Variable Gap Magnet
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computer interface
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multimeter or galvanometer
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patch cords
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small strips of masking tape
Purpose
The purpose of this experiment is to detail the operation of an AC generator and a DC
generator in terms of basic concepts of electromagnetism.
Theory
Motors and generators may be regarded as devices that convert energy from one form to
another. A motor converts electrical energy into mechanical energy. Many designs of
motors work as generators as well: when mechanical energy is input by spinning the shaft,
electrical energy is produced. More than one line of reasoning may be used to predict the
magnitude and direction of the electrical current that is produced. At the most fundamental
level, electrical charges moving across a magnetic field experience a force that is at right
angles to both the direction of motion and the direction of the magnetic field, according to
the vector equation:
F=qV x B
Conductors, of course, contain charges, and moving a conductor sideways across a
magnetic field causes a force on the charges that may make the charges flow the length of
the conductor if it is part of a circuit. The force on the charges can be seen from the
equation to be proportional to both the speed and the strength of the magnetic field.
From this reasoning you can derive Faraday’s law of electromagnetic induction, which
states that a change in the magnetic flux linking a closed circuit will result in an electromo-
tive force (or electric current) in the circuit that is instantaneously proportional to the time
rate of change of the linking flux; however, it is easier to understand Faraday’s law by
observing the action of a generator. In a generator, an electromotive force (emf) that is
proportional to the rate of change is induced in a loop of wire that is in a field of changing
magnetic flux. (The coils of the armature may thought of as many loops connected in
series.)
Experiment 2: Operation of AC and DC Generators