Elenco Upgrade Kit SC500 to SC750 - Manual (Page 69)

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Project #656
OBJECTIVE: To learn about the electromagnet.
Electromagnet
Delayer
Build the circuit and turn it on. After a delay of about 2 seconds, the
lamp (L2) will light, but be dim. Replace your batteries if it does not light
at all.
Why does the electromagnet (M3) delay the lamp turn-on? The
electromagnet (M3) contains a large coil of wire, and the batteries have
to fill the coil with electricity before the lamp can turn on. This is like
using a long hose to water your garden - when you turn on the water it
takes a few seconds before water comes out the other end.
Once the lamp is on, the resistance of the wire in the coil keeps the
lamp from getting bright. You can replace the 6V lamp with the 2.5V
lamp (L1), because the coil will protect it from the full battery voltage.
Project #657
OBJECTIVE: To learn about the electromagnet.
Electromagnet
Delayer (II)
Use the LOW (or 10mA) setting on the meter (M2) and turn on the
slide switch (S1). The meter shows how the current slowly rises. After
a delay of about 2 seconds, the lamp (L2) will light but be dim.