Project 57
Electromagnet Challenge
Assemble the build-your-own electromagnet
(the thin wire wrapped around an iron core rod,
with the ends connected to the 2-spring socket
(?1)) using the instructions on page 5. Build the
circuit, place the iron core rod in the electromag-
net (M3).
Set the switcher (S6) to the left position to turn
on the build-your-own electromagnet, set it to
the right position to turn on the M3 electromag-
net, or set it to the middle position to turn off the
circuit. Move the compass around to compare
the magnetic fields from the two electromagnets.
Connect several paperclips into a chain and hold
near each electromagnet, comparing them.
To turn on both electromagnets at the same
time, connect a 3-snap wire between the 2-
spring socket and the M3 electromagnet (over
the switcher), and set the switcher to either the
left or right position.
This circuit isn’t really a fair
comparison between the
build-your-own and M3 elec-
tromagnets, because the
build-your-own electromag-
net is in series with the
lamps (L4). The lamps limit
the current through the
build-your-own electromag-
net (to avoid triggering the
safety fuse), but also lower
its power. The M3 electro-
magnet has enough resist-
ance to avoid triggering the
safety fuse.
Project 58
Coil Resistance
Build the circuit shown and set the meter (M5) to
the 5V setting. Set the switcher (S6) to the bottom
position; the meter shows that the full battery volt-
age is across the white LED (D6, and the LED is
very bright.
Now set the switcher to the top position to place
the electromagnet (M3) and relay (S3) in series
with the white LED. The voltage is a little lower
now, and the LED is not as bright.
Next, replace the white LED with a lamp (L4). Com-
pare the difference in lamp brightness with the
switcher in the top and bottom positions.
The wire in the coils of the
electromagnet and relay is
long enough to have no-
ticeable resistance; this re-
sistance makes the white
LED a little less bright, and
prevents the lamp from
lighting at all.
5V
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