The direction of a magnetic
field from a current flowing in
a wire (or coil of wire) de-
pends on the direction of the
electric current.
Project 50
Electromagnet Direction
Build the circuit shown. Place the iron core rod in the electromagnet (M3), and set the meter (M5) to the
1A scale. Set the switcher (S6) to the top or bottom position. The meter shows a current is flowing
and the compass needle is attracted to the electromagnet.
Now set the switcher to the opposite side (left or right). The other side of the compass needed
is attracted to the electromagnet (magnetic field is reversed). In some cases you may need
to hold the compass closer to the electromagnet for the needle to change sides.
If you remove the iron core rod from the electromagnet, the compass needle attraction will
be much weaker. Try moving the rod in and out while watching the compass.
1A
Project 51
Wire Magnet
Build the circuit as shown. Note that the 5-snap wire is connected on level 4 on the left side
and at level 3 on the right side, over the compass; make sure it is securely snapped. This circuit
works best with new alkaline batteries. Keep the circuit away from any iron objects.
Turn on the slide switch (S1) and switch the switcher (S6) between the top and bottom positions
repeatedly while watching the compass. You should see the compass needle move a little - in-
dicating a change in the magnetic field from the 5-snap wire (the “wire magnet”“).
Note:
The magnetic field produced by the wire is very small. If the compass needle does not
move, check your batteries (B3) and make sure you are not close to any iron objects.
The three lamps (L4) are in this circuit to
limit the current; without them the circuit
would have almost no resistance (since
the only components would be switches
and wires). Then the “wire magnet”
would have a stronger magnetic field,
but the higher current would trigger a
safety fuse in your battery holder, which
would quickly shut down the circuit.
Any electric current flowing in
a wire has a magnetic field,
but it is usually very small. An
electromagnet creates a no-
ticeable magnetic field by
looping the wire very many
times to concentrate the
magnetic field from it.
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