Elenco 130-in-1 Electronics Playground - Manual (Page 120)

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The circuit in this experiment allows you to hear
alternating current. You probably know that the
electric power running through your home is an
alternating current. All your appliances that receive
power from electric outlets operate on AC- including
lamps. Lamps actually flicker at the rate of 60 times
per second, but it looks constant because our eyes
see after images. In this experiment you will hear
sound converted from light.
Ready to start? After constructing this circuit, turn on
the power to your kit by setting the switch to A. Place
the CdS cell near an electric lamp. Do you hear a
hissing sound coming from the earphone? This is the
sound of the alternating current. Now place the CdS
cell under a fluorescent lamp, and listen for a similar
sound.
This circuit greatly intensifies the signals of light on
the CdS cell through the operational amplifier. Adjust
the quantity of light on the CdS cell with your hand.
You can probably hear the volume of the hissing
sound reduce and the quality of the sound improve.
See what occurs when you expose the CdS to
sunlight.
Notes:
EXPERIMENT #100: LISTEN TO ALTERNATING CURRENT
Schematic
Wiring Sequence:
15-88-113
87-63-131
76-93-68
70-121
69-90
75-99-114
122-132
67-94-81-13-EARPHONE
124-119-16-100-89-82-14-EARPHONE