The Science of the potato clock

In the potato clock, the water inside the potatoes combines with the metal spikes attached to the wires to create a very simple battery.

Some of the spikes have Copper on the end, and the others have Zinc. Zinc is the anode for the battery - that means that it has some "spare" electrons that it can loose into the salty water. The copper acts as a cathode which means that it can receive the electrons.

Of course, to get from one to the other, the electrons have to move around the circuit and moving electrons is electricity!

The circuit here can produce about half a Volt, which is just about enough to power the small LCD clock here. This kind of battery is not enough for most things though (a typical digital camera needs about 6 Volts).