Making a battery from a potato is a great way to learn about how simple chemical reactions can power a circuit. The supplies you need for this project are very inexpensive, and it only takes a few minutes to put it together. Making a battery using a potato is a simple activity, but it can help to give you a greater appreciation for and understanding of what's going on inside of more complicated batteries.
What You Will Need
For a very basic potato battery, all you need is a potato, a knife, two short pieces of copper wire, a shiny penny and a galvanized nail or screw. If you want to chain together multiple cells to make a more powerful battery, then you will need a penny and a nail or screw for each cell. A multimeter is optional for this activity, but having one ready will allow you to more easily test the battery that you are making.
Putting Together the Battery
Start off by cutting a small slit near one end of the potato. Tightly wrap the copper wire around the penny two or three times, and then push the penny into the slit you cut in the potato until the penny is only barely sticking out. Insert the galvanized screw or nail into the opposite end of the potato, and wrap the other piece of copper wire around the screw or nail so that it's tight. At this point, you should have a potato with a copper wire coming out of each end. These two copper wires are the leads for your potato battery.
Testing Your New Battery
If you have a multimeter ready, then you can check the voltage of the potato battery by connecting one lead to each of the copper wires. The average potato battery can generate anywhere from 0.4 to 0.8 volts. It's possible to use a small light bulb or light-emitting diode to test your potato, but it may not produce enough voltage to work. In this case, you will need to build two or three potato batteries connected in series to get the desired result.
How the Battery Works
What you have created with your potato is an example of an electrochemical cell. This means that the potato battery is using a set of chemical reactions to produce electricity. The copper in the penny reacts with the contents of the potato in a way that causes an accumulation of electrons. The same reaction happens to the zinc in the screw or nail, but it happens on a smaller scale.
Once these electrons have built up, you have a situation where there is a large imbalance between the number of electrons in the copper and the number of electrons in the zinc. If you place a circuit like an LED or a multimeter between the two ends of the potato, then the electrons will flow between the two metals to try to correct the imbalance. This flow of electrons is what powers the circuit. As long as the electrons keep flowing, your battery will keep working.