Potato Clock or Potato Battery

The potato clock science project teaches students the principle behind the working of a battery. The experiment is an ideal one to be performed at science fairs to invoke curiosity in kids on the science behind current and electricity. It is good to have some background information on the traveling of current from the positive to the negative terminal of a battery and that of electrons in the opposite direction before embarking on the investigation. Then, in case the potato battery clock does not work, they know how to troubleshoot.

How to Make a Potato Battery

Hypothesis

On making the connections as explained below, 2 potatoes power a LED clock that has its actual battery removed.

Materials

• 2 potatoes
• 2 galvanized nails
• 2 small pieces of heavy copper wire
• 3 alligator clips
• Marker pen
• A low voltage LED clock that uses a 1-2 volt button type battery

Instructions

1. Remove the battery from the clock making a note of which end (positive or negative) of the battery went to which terminal point in the battery compartment of the clock.
2. Number the potatoes as 1 and 2 with the marker.
3. Insert a nail in each potato.
4. Insert a copper wire into each potato a far away from the nail as possible.
5. Use an alligator clip to connect the copper wire in potato 1 to the positive terminal in the battery compartment of the clock.
6. Connect the nail in potato 2 to the negative terminal in the battery section of the clock using the alligator clip.
7. Connect the nail in potato 1 to the copper wire in potato 2 with the 3^rd alligator clip and watch the clock turn on.

Note that the battery lasts for only a short span of time. Drawing the circuit diagram prior to conducting the experiment minimizes the chances of errors.

Potato Powered Clock Video

Here is a video to help you carry out the building procedure.

How Does a Potato Clock Work

Being an electrochemical cell, a potato battery transforms chemical energy into electrical energy. A transfer of electrons takes place between the zinc coating of the galvanized nails and the copper wire inserted in the potatoes with the help of the alligator clips that complete the circuit resulting in a chemical reaction. Here the potato provides a favorable medium for the transfer of the electrons. That charges the clock.

Fun Facts

• Research has shown an easily available and a green source of energy, potato clocks, could power cell phones and other small electronic appliances in remote, underdeveloped places having no access to a power grid.
• Boiling the potatoes further increases their electrical conductivity.

You Can Try

• Test if it can power a digital alarm clock, light bulb and flashlight. You might have to play around with the number of potato pairs connected in series to achieve the objective.
• Substitute the copper wires with copper pennies. Does it work?
• Can you measure the voltage supplied by the potato battery? Consider using a voltmeter or a multimeter for this.

A lemon battery utilizes a similar theory. Hence, after doing the activity with potatoes, you can repeat with lemons, bananas and apples and check the voltage and/or brightness supplied by them. A data chart for the observations and a graph with the voltage as the dependent variable and the fruits and vegetable as the independent one could make the comparative study easier. You may also prepare a display board to demonstrate the DIY tutorial in the lab.