A Lemon Battery is a device used in experiments proposed in many science textbooks around the world. It is made by inserting two different metallic objects, for example a galvanized nail and a copper coin, into a lemon.
The copper coin serves as the positive electrode or cathode and the galvanized nail as the negative electrode or anode. These two objects work as electrodes, causing an electrochemical reaction which generates a small potential difference.
The aim of this experiment is to show students how batteries work. After the battery is assembled, a multimeter can be used to check the generated voltage. In order for a more visible effect to be produced, a few lemon cells connected in series can be used to power a standard LED. Flashlight bulbs are generally not used because the lemon battery cannot produce the amount of current required to light such bulbs.