WHAT’S HAPPENING
The electromagnet attracts the met-
al strip to touch its pole. When that
happens, the electric circuit is
closed and the light shines. When
you break the circuit, the light
turns off and the strip springs back.
HERE’S HOW
Remove the metal prong fastener strip from a
folder, and use a piece of sandpaper to roughen
up its surface to about three centimeters from
both ends. Attach the fastener strip to the hang-
er device by partly wrapping the strip around it
and then securing it with tape. Its end should be
about three centimeters above the table surface
when the hanger is standing upright.
Connect the horseshoe electromagnet to the
battery case via switch, plug wire, and X- and
L-connectors.
Assemble a second circuit with light, I-connec-
tors, and both alligator wires. One of the alli-
gator wires will lead from the light to one of
the bare poles of the horseshoe electromagnet.
Clamp one end of the other wire to the battery’s
second terminal and the other end to the metal
fastener strip, near where you attached it.
Arrange the horseshoe electromagnet and the
hanger in such a way that the magnetic poles
and the strip are at the same height. Place a
book under the horseshoe electromagnet if
necessary.
The magnet should only touch the metal strip
when it is switched on. When that happens, one
of the two bare arms of the horseshoe electro-
magnet should touch a part of the metal strip
that you rubbed bare.
Now, when you send current through the elec-
tromagnet, the bulb will light up. What do you
see when you switch the current off?
Remote
control
If an electromagnet can attract
iron, it can also open and close
an electrical contact. This kind
of arrangement is known as a
“relay.” Relays have many uses
in electrical engineering.
EXPERIMENT 61
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