A lemon battery is a classic science experiment used to demonstrate the basics of a chemical battery system. To conduct this experiment, a scientist needs one very juicy lemon, a galvanized or zinc-coated steel nail, and a clean copper coin or section of household copper wiring. The scientist making the battery also needs a wire with alligator clips at each end and a sensitive voltmeter. Voltmeters can usually be found in the electrical supply section of a hardware store, electronic hobby store, or home improvement center. Small Light-Emitting Diodes (LEDs) and other electrical devices can also be used to test a lemon battery, though this typically requires additional lemons.
How it Works
A lemon battery relies on electrons and a chemical reaction that takes place when metals are introduced to an acidic mixture. The lemon contains a significant amount of acidic juice, which in scientific terminology is an "electrolyte." Acid in an electrolyte helps break down the atomic structure of metals, like copper and zinc, causing the release of individual electrons. When a scientist creates a circuit, by connecting the two metals with a conductor, the electrons flow through it as an electrical charge, which can be detected on a voltmeter or other device.
Making the Battery
First, the scientist creating a lemon battery should carefully insert the copper coin or household copper wiring into one end of the lemon, then insert the galvanized nail into the opposite end. It is important for the scientist doing this to make sure the two metals do not make contact with each other. This would close the circuit, and holding the metals while they touch could result in a mild electric shock.
Creating the Charge
The nail and the coin have now become electrodes. Both copper and zinc allow electrons to flow through them, which means they are considered excellent conductors of electricity. The copper coin or wire is considered a positive (+) electrode, while the zinc-coated nail is a negative (-) electrode.
Free-flowing electrons found in the lemon-juice electrolyte naturally want to move from the negative to the positive electrodes. How fast these electrons flow is measured as amperage. The voltmeter picks up on this by displaying voltage, which indicates the "electrical pressure" working within the circuit.
A single lemon battery does not produce a significant amount of voltage, but a sensitive voltmeter should detect some electrical output. The scientist should connect the positive clip of a wire, the end with a red casing, to the copper coin or wire; and the negative clip, the end with a black casing, to the galvanized nail. A digital readout or analog dial on the voltmeter should show a small voltage number, usually less than one-tenth of a volt. This is not typically enough to run a digital clock or power a light bulb, but it does demonstrate that an electrical current has been generated through a chemical reaction within the lemon battery.
Increasing the Charge
While a single-cell lemon battery is functional, it provides little meaningful electrical charge. Additional voltage can be provided by increasing the number of cells, or lemons, within the battery. A series of lemons can function together as a single battery through additional wires attached from the positive electrode, copper part, of one lemon to the negative end, zinc nail, of another.
About four lemons connected in series in this way should provide enough power to light a small LED. The scientist should connect the negative lead from one end lemon to the LED wire closest to a flattened area of the casing. He or she can then connect a positive lead, from the other end lemon, to the other wire. A dim but noticeable glow should light in the center of the LED; additional lemons or cells can be added to the battery for greater charge and an even brighter glow.