Elenco Electronics 202 - Manual (Page 46)

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Project #80
OBJECTIVE: To show that the fan blade stores energy.
Fan Blade Storing Energy
Place the fan on the motor (M1). Hold down the press switch (S2) for
a few seconds and then watch the LED (D1) as you release the switch.
The LED lights briefly but only after the batteries (B1) are
disconnected from the circuit.
Do you know why the LED lights? It lights because the mechanical
energy stored in the fan blade makes the motor act like a generator.
When the switch is released, this energy creates a brief current
through the LED. If you remove the fan blade from the circuit then the
LED will never light, because the motor shaft alone does not store
enough mechanical energy.
If you reverse the motor direction, then the LED will light the same way,
but the fan may fly off after the LED lights.
!
WARNING: Moving parts. Do not
touch the fan or motor during operation.
!
WARNING: Do not
lean over the motor.
Project #81
Photo Timer Light
OBJECTIVE: To show how
capacitors store energy.
Project #82
NPN Light Control
OBJECTIVE: To compare
transistor circuits.
Turn on the slide switch (S1), the
brightness of the LED (D1)
depends on how much light
shines on the photoresistor (RP).
The resistance drops as more
light shines, allowing more current
to the NPN transistor (Q2).
Press and release the press
switch (S2), then turn on the slide
switch (S1). The LED will light for
a while when there is light on the
photoresistor (RP).
The capacitor (C5) will store
energy until a light shines on the
photo resistor to release the
energy, which activates the NPN
transistor (Q2) and turns on the
LED (D1). Press the press switch
again to recharge the capacitor.