Lemon battery

There are many variations of the lemon cell that use different fruits (or liquids) as electrolytes and metals other than zinc and copper as electrodes.

There are numerous sets of instructions for making lemon batteries and for obtaining components such as light-emitting diodes, (LEDs), electrical meters (multimeters), and zinc-coated (galvanized) nails and screws.

For a more visible effect, lemon cells can be connected in series to power an LED (see illustration) or other devices.

Swartling and Morgan have published a list of low-voltage devices along with the corresponding number of lemon cells that were needed to power them; they included LEDs, piezoelectric buzzers, and small digital clocks.

Such a battery typically produces 0.001 A (1 mA) of current at a potential difference of 0.7 V; these values are multiplied together to determine the overall power of 0.0007 W (0.7 mW).

Other metals such as lead, iron, magnesium, etc., can be studied as well; they yield different voltages than the zinc/copper pair.

For older pupils and for college students, batteries serve to illustrate the principles of oxidation-reduction reactions.

This model of the chemical reactions makes several predictions that were examined in experiments published by Jerry Goodisman in 2001.

Goodisman notes that numerous recent authors propose chemical reactions for the lemon battery that involve dissolution of the copper electrode into the electrolyte.

When the electrolyte was modified by adding zinc sulfate (ZnSO4), the voltage from the cell was reduced as predicted using the Nernst equation for the model.

This result is consistent with the fact that copper atoms from the electrode are not involved in the chemical reaction model for the cell.

The two oxidation-reduction reactions listed above only occur when electrical charge can be transported through the external circuit.

From 1840 to the late 19th century, large, voltaic cells using a zinc electrode and a sulfuric acid electrolyte were widely used in the printing industry.

[18][19] Hydrogen gas clinging to the surface of a silver or copper electrode reduces the electric current that can be drawn from a cell; the phenomenon is called "polarization".

[17][20] The roughened, "platinized" surface speeds up the bubbling of the hydrogen gas, and increases the current from the cell.

The Smee cell was convenient for electrotyping, which produced copper plates for letterpress printing of newspapers and books, and also statues and other metallic objects.

A drawing showing three lemons and a glowing red object (the LED). The LED has two lines coming out of its bottom to represent its electrical leads. Each lemon has two metal pieces stuck into it; the metals are colored differently. There are thin black lines, representing wires, connecting the metal pieces stuck into each lemon and the leads of the LED.
Diagram showing three lemon cells wired together so that they energize the red light-emitting diode (LED) at the top. Each individual lemon has a zinc electrode and a copper electrode inserted into it; the zinc is colored gray in the diagram. The slender lines drawn between the electrodes and the LED represent the wires.
Photograph of a potato. A copper wire is stuck into the potato, and an insulated lead wire is connected to the top of it using a nut and screw. A galvanized machine screw is also suck into the face. There is a nut that is next to the screw head; the second lead wire is squashed between the head and the nut. A "+" symbol is marked on the potato's skin near the copper wire that is stuck into it.
Potato battery with zinc (left) and copper electrodes. The zinc electrode is a galvanized machine screw. The copper electrode is a wire. Note the labels āˆ’ and + marked on the potato indicating that the copper electrode is the positive terminal of the battery. A short screw and nut connect the electrodes to the copper wires that have black and red insulating plastic coatings.
Cross-section drawing of a cup. The cup is mostly full, apparently with water. Two rectangular shapes indicate a copper and a zinc piece, each of which is mostly submerged in the water. The water has about a dozen symbols in various positions: Zn2+, H+, and SO42āˆ’. There's a circle above the water with the symbol H2 inside it. There's a wire connecting the zinc and copper pieces outside of the water; 2 electrons (eāˆ’) are shown along the wire with arrows pointing from the zinc to the copper.
Cross-section of a copper/zinc cell with a sulfuric acid electrolyte. The drawing illustrates the atomic model for the chemical reactions; lemon cells have essentially the same model. Zinc atoms enter the electrolyte as ions missing two electrons (Zn 2+ ). Two negatively charged electrons from the dissolved zinc atom are left in the zinc metal. Two of the dissolved protons (H + ) in the acidic electrolyte combine with each other and two electrons to form molecular hydrogen H 2 , which bubbles off of the copper electrode. The electrons lost from the copper are made up by moving two electrons from the zinc through the external wire.