Homemade apple batteries are one method of teaching kids about electricity. While an apple will not conduct enough electricity to power a light bulb, you can verify the electricity level with a voltmeter. If you do not have apples handy, try substituting a lemon, orange or even a potato. This experiment works by using a nail and a wire as terminals, and the juice of the apple acts as an electrolyte through which ions can flow.
Rub the end of a zinc plated or galvanised nail gently with sandpaper.
Strip the insulation off an 18-gauge copper wire. The wire should be about 4 inches long. If you use a knife to strip the insulation off, be careful to push it away from you to avoid cuts.
Clean both ends of the wire gently with the sandpaper.
Insert the nail about 2 inches down into the apple.
Insert one end of the copper wire into the apple at the same depth as the nail. The wire should be as close as possible to the nail without touching it, or about 2 centimetres away. The nail and the wire make up the two terminals in the apple battery.
Turn on a voltmeter.
Touch the red meter lead to either the nail or the wire. Touch the black meter lead to the other terminal.
Look at the voltmeter's display. If it does not display a voltage, switch the meter leads around so that they each touch a different terminal. The voltage displayed in the voltmeter is the amount of electricity that your apple battery is conducting.
If the two terminals touch, take them out and try the experiment again in a different part of the apple. Touching the terminals together shorts the battery.