The lemon battery is called a voltaic battery, which changes chemical energy
into electrical energy.
The battery is made up of two different metals (the steel paper clip and the copper
wire). These are called electrodes, which are the parts of a battery where
electric current enters or leaves the battery. The electrodes are placed in a liquid
containing an electrolyte, which is a solution that can conduct
In a solution of water and an electrolyte, like the acid in the lemon, an excess of
electrons collects on one end of the electrodes. At the same time, electrons are lost
from the other electrode.
Touching the electrodes to your tongue closes the circuit and allows an small electric
current to flow. A single lemon produces about 7/10 of a volt of electricity. If you
connected two lemons together, you can power an inexpensive digital watch (uses
about 1.5 volts). (Use a length of thin, flexible wire to connect the silver wire of one
lemon to the copper wire of the other lemon. Then attach thin wires from the other
two wires in the lemons to where a battery's positive and negative poles connect to
power the watch.)
The tingle felt in your tongue and the metallic taste is due to the movement of
electrons through the saliva on your tongue.
Note About Lemon Energy
We've had some students do this project and then try to use the lemon "battery" to light a small flashlight's light bulb. The lemons did not work. Why? The reason is that the lemons produce only a very small current (about one milliamp). This is not enough electric current to light the bulb. Even with multiple lemons, the amount of current flowing through the wire is not enough. Though the voltage is high enough (1.5 volts with two lemons), the current is too weak. But it was a great experiment! Even if an experiment doesn't work, it helps us to understand how things work. Good work!!!