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 red light emitting diode *

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.

• Note what happens right when you connect the battery. Remember that the red LED only works one way, so reverse it if nothing is happening.
• 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.
• 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.

Check the box when you are done:  
Next:Science content: electromagnetism