How does a potato clock work?

early potatoes image by Maria Brzostowska from

The famed potato clock seems impossible, but an easy science experiment can give you insight into how this basic battery works. You already have most of the materials you need. A trip to the basement work area, the pantry and the kitchen drawer may help you complete your recipe for a potato clock.

You'll need two galvanised nails, several inches of copper wire and wire clips, an LED clock with the battery removed, and a potato or two.

Assemble the Clock

Assemble the clock by first putting one nail into each potato or potato half. Insert a length of copper wire into each potato or potato piece such that it does not touch the nail. Take one part of the two-piece potato battery and attach the copper wire to the positive end of the LED clock's battery attachment. Take the second part of the potato battery--the other potato-wire/nail combo--and attach the zinc-coated nail to the negative portion of the LED clock's battery attachment. Attach the remaining zinc nail and copper wire together, completing the circuit.

How it Works

An electrochemical battery stores chemical energy that changes into electrical energy that runs electronic equipment. There is a chemical reaction within the potato battery that causes the electrons to move. The electromotive force within each potato is the ability it carries to move electric current. In an electrochemical cell, such as the potato battery, the copper wire makes the electrons move in the potato, causing energy to move into the clock.

The official scientific name for the chemical reaction is "redox reaction." The process starts when one side of the battery loses electrons. This happens in the zinc nail, which forms the anode, or positive part of the circuit. The zinc in the nail reacts with phosphoric acid in the potato, releasing electrons. The zinc loses two electrons while the copper in the wire reacts with the phosphoric acid to release hydrogen ions, which gain the electrons. This is the negative half of the circuit, or the cathode, which thereby gains the electrons.