Elenco Electronics 202 - Manual (Page 104)

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This AM radio circuit uses a transistor (Q2) in the amplifier that drives
the speaker (SP). Turn on the slide switch (S1) and adjust the variable
capacitor (CV) for a radio station, then adjust the loudness using the
adjustable resistor (RV).
Project #245
OBJECTIVE: To show the output of an AM radio.
Transistor AM Radio
Hold down the press switch (S2) 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.
This circuit is different from the Fan Blade Storing Energy project,
because energy in the antenna coil (A1) is stored in a magnetic field.
When the switch is released, this field creates a brief current through
the LED.
Note that the energy stored in a magnetic field acts like mechanical
momentum, unlike capacitors which store energy as an electrical
charge across a material. You can replace the antenna with any of the
capacitors but the LED will not light. Energy stored in the magnetic
fields of coils was called electrical momentum in the early days of
electronics.
Project #246
OBJECTIVE: To show that the antenna stores energy.
Antenna Storing
Energy