Not only can a current make a magnetic field, a changing magnetic field
can try to make currents flow. This activity gives an example.
Assemble these materials:
the electromagnet you made, with the large nail inside it
one battery holder and battery *
wires with alligator clip ends *
a bipolar light emitting diode (that turns green or red,
depending on how it is connected to two batteries). *
Compare the behavior of these two circuits, where we will use
only a single battery (1.5 V):
In these diagrams, the switch just means that we don't
permanently connect the battery into the circuit -- instead, just
touch the battery wire to the other parts, to see what happens when
you give the circuit a short jolt or a longer application of the
voltage. Nothing is supposed to happen in the circuit at left --
the voltage is not big enough to operate the LED (but we check,
anyway).
The circuit at right is more interesting.
Compare what happens if you connect the battery for a few
seconds to what happens if you just quickly touch the battery wire
to the rest of the circuit.
Compare what happens if you remove the nail from the
electromagnet.
A motor contains an electromagnet. See what happens if you
replace the electromagnet by the motor in the circuit at right,
above. There are two things to try: just letting the motor run, or
holding the motor shaft so that it cannot turn, as you connect and
disconnect the battery.