Each experiment will need two potatoes, which will replace a 2-volt battery. They will also require two short pieces of heavy copper wire (which will conduct the electricity), two galvanized nails and a simple, low-voltage LED clock (or an LED light, if one cannot be found). Three alligator clips connected to each other with wire are also necessary.
After removing the battery from the clock, make a note where the negative and positive points of the battery are pointed. Label one potato positive and the other negative and press one nail into the side of each. Press one of the copper wires into the opposite side of each potato, as far from the nail as possible. Use an alligator clip to connect the copper wire in the positive potato into the positive terminal in the clock. Use another alligator clip to connect the nail in the negative potato into the negative terminal. Turn the clock on and watch it work.
The chemical energy in the potato reacts with the zinc in the nail and the copper in the wire to produce a spontaneous electron transfer. These electron transfers create electric energy. If the zinc and the copper were to touch inside the potato, they would generate heat rather than electrical energy.
The alligator clips can be attached to the wires of an LED light rather than the terminals of a clock or may be used to power other small electrical objects. One fun continuation of the experiment could be for students to try to use the potato batteries to operate increasingly powerful objects. Another possibility is to try the experiment with a variety of potato types to compare longevity of the batteries.