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Electromagnetism
Reversible demonstration alternator
Réf :
292 075
ENGLISH
2. The LED blinks if the value of the voltage at its terminals is sufficiently
high, which demonstrates the existence of a «threshold voltage» as for all
diodes.
3. The LED limits the voltage in the conducting direction.
2.3.3 Voltage as a function of the relative position of the coil
and magnets
When the alternator turns slowly, the plot of the voltage curve as a function of
time and the position of the rotor (the rotating part of the alternator) relative to
the stator (the fixed part of the alternator) can be observed simultaneously.
Coil axis perpendicular to
the straight line joining the
mid-points of the magnets
It is found that:
1. the maximum and minimum voltages are obtained when the coil axis is
perpendicular to the straight line joining the magnets.
2. the voltage is zero when the coil axis is coincident with the straight line
joining the magnets.
Note : With the Visio (and Visio plus) console, the alternator can be filmed in
movement during acquisition of the voltage. Thus, the variation of the voltage
during time and the position of the coil relative to the magnets can be
observed, image by image and simultaneously.
Starting from these observations, the alternation of the voltage and the
direction of the winding in coil turns relative to a magnet can be related to each
other.
The concept of magnetic flux can then be introduced, depending on the study
level.
2.3.4 Influence of the coil rotation direction on the voltage
produced
The coil is connected to an interface connected to the computer. The polarity
of the magnets is identified using a magnetized needle and the south pole of a
magnet is placed facing the face of the coil connected to the safety bushings.
15
Coil of axis coincident with
the straight line joining the
mid-points of the magnets
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