A lemon battery is a simple
battery
Battery most often refers to:
* Electric battery, a device that provides electrical power
* Battery (crime), a crime involving unlawful physical contact
Battery may also refer to:
Energy source
*Automotive battery, a device to provide power t ...
often made for the purpose of education. Typically, a piece of
zinc
Zinc is a chemical element with the symbol Zn and atomic number 30. Zinc is a slightly brittle metal at room temperature and has a shiny-greyish appearance when oxidation is removed. It is the first element in group 12 (IIB) of the periodi ...
metal (such as a
galvanized
Galvanization or galvanizing ( also spelled galvanisation or galvanising) is the process of applying a protective zinc coating to steel or iron, to prevent rusting. The most common method is hot-dip galvanizing, in which the parts are submerged ...
nail) and a piece of
copper
Copper is a chemical element with the symbol Cu (from la, cuprum) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkis ...
(such as a penny) are inserted into a
lemon
The lemon (''Citrus limon'') is a species of small evergreen trees in the flowering plant family Rutaceae, native to Asia, primarily Northeast India (Assam), Northern Myanmar or China.
The tree's ellipsoidal yellow fruit is used for culin ...
and connected by wires. Power generated by reaction of the metals is used to power a small device such as a
light-emitting diode
A light-emitting diode (LED) is a semiconductor device that emits light when current flows through it. Electrons in the semiconductor recombine with electron holes, releasing energy in the form of photons. The color of the light (cor ...
(LED).
The lemon battery is similar to the
first electrical battery invented in 1800 by
Alessandro Volta
Alessandro Giuseppe Antonio Anastasio Volta (, ; 18 February 1745 – 5 March 1827) was an Italian physicist, chemist and lay Catholic who was a pioneer of electricity and power who is credited as the inventor of the electric battery and the ...
, who used
brine
Brine is a high-concentration solution of salt (NaCl) in water (H2O). In diverse contexts, ''brine'' may refer to the salt solutions ranging from about 3.5% (a typical concentration of seawater, on the lower end of that of solutions used for br ...
(salt water) instead of lemon juice.
The lemon battery illustrates the type of
chemical reaction
A chemical reaction is a process that leads to the IUPAC nomenclature for organic transformations, chemical transformation of one set of chemical substances to another. Classically, chemical reactions encompass changes that only involve the pos ...
(
oxidation-reduction) that occurs in batteries.
The zinc and copper are called the
electrode
An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit (e.g. a semiconductor, an electrolyte, a vacuum or air). Electrodes are essential parts of batteries that can consist of a variety of materials de ...
s, and the juice inside the lemon is called the
electrolyte
An electrolyte is a medium containing ions that is electrically conducting through the movement of those ions, but not conducting electrons. This includes most soluble salts, acids, and bases dissolved in a polar solvent, such as water. Upon dis ...
. 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.
Use in school projects
There are numerous sets of instructions for making lemon batteries and for obtaining components such as
light-emitting diode
A light-emitting diode (LED) is a semiconductor device that emits light when current flows through it. Electrons in the semiconductor recombine with electron holes, releasing energy in the form of photons. The color of the light (cor ...
s (LEDs), electrical meters (
multimeter
A multimeter is a measuring instrument that can measure multiple electrical properties. A typical multimeter can measure voltage, resistance, and current, in which case it is also known as a volt-ohm-milliammeter (VOM), as the unit is equipped w ...
s), and zinc-coated (
galvanized
Galvanization or galvanizing ( also spelled galvanisation or galvanising) is the process of applying a protective zinc coating to steel or iron, to prevent rusting. The most common method is hot-dip galvanizing, in which the parts are submerged ...
) nails and screws.
Commercial "potato clock" science kits include electrodes and a low-voltage digital clock. After one cell is assembled, a
multimeter
A multimeter is a measuring instrument that can measure multiple electrical properties. A typical multimeter can measure voltage, resistance, and current, in which case it is also known as a volt-ohm-milliammeter (VOM), as the unit is equipped w ...
can be used to measure the
voltage
Voltage, also known as electric pressure, electric tension, or (electric) potential difference, is the difference in electric potential between two points. In a static electric field, it corresponds to the work needed per unit of charge to m ...
or the
electric current
An electric current is a stream of charged particles, such as electrons or ions, moving through an electrical conductor or space. It is measured as the net rate of flow of electric charge through a surface or into a control volume. The moving pa ...
from the voltaic cell; a typical voltage is 0.9 V with lemons. Currents are more variable, but range up to about 1 mA (the larger the electrode surfaces, the bigger the current). For a more visible effect, lemon cells can be connected in
series
Series may refer to:
People with the name
* Caroline Series (born 1951), English mathematician, daughter of George Series
* George Series (1920–1995), English physicist
Arts, entertainment, and media
Music
* Series, the ordered sets used in ...
to power an LED (see illustration) or other devices. The series connection increases the voltage available to 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. With the zinc/copper electrodes, at least two lemon cells were needed for any of these devices.
Substituting a magnesium electrode for the zinc electrode makes a cell with a larger voltage (1.5−1.6 V), and a single magnesium/copper cell will power some devices.
Note that
incandescent
Incandescence is the emission of electromagnetic radiation (including visible light) from a hot body as a result of its high temperature. The term derives from the Latin verb ''incandescere,'' to glow white. A common use of incandescence is ...
light bulbs from flashlights are not used because the lemon battery is not designed to produce enough electric current to light them. By multiplying the average current of a lemon (0.001A/ 1mA) by the average (lowest) voltage (potential difference) of a lemon (0.7V) we can conclude that it would take more than 6 million lemons to give us the power of an average 4320W car battery.
Variations
Many fruits and liquids can be used for the acidic electrolyte. Fruit is convenient, because it provides both the electrolyte and a simple way to support the electrodes. The acid involved in
citrus fruits
''Citrus'' is a genus of flowering trees and shrubs in the rue family, Rutaceae. Plants in the genus produce citrus fruits, including important crops such as oranges, lemons, grapefruits, pomelos, and limes. The genus ''Citrus'' is nativ ...
(lemons, oranges, grapefruits, etc.) is
citric acid
Citric acid is an organic compound with the chemical formula HOC(CO2H)(CH2CO2H)2. It is a colorless weak organic acid. It occurs naturally in citrus fruits. In biochemistry, it is an intermediate in the citric acid cycle, which occurs in t ...
. The acidity, which is indicated by the measured
pH, varies substantially.
Potato
The potato is a starchy food, a tuber of the plant ''Solanum tuberosum'' and is a root vegetable native to the Americas. The plant is a perennial in the nightshade family Solanaceae.
Wild potato species can be found from the southern Unit ...
es have
phosphoric acid
Phosphoric acid (orthophosphoric acid, monophosphoric acid or phosphoric(V) acid) is a colorless, odorless phosphorus-containing solid, and inorganic compound with the chemical formula . It is commonly encountered as an 85% aqueous solution, w ...
and work well; they are the basis for commercial "potato clock" kits. Potato batteries with
LED
A light-emitting diode (LED) is a semiconductor Electronics, device that Light#Light sources, emits light when Electric current, current flows through it. Electrons in the semiconductor recombine with electron holes, releasing energy i ...
lighting have been proposed for use in poor countries or by off-grid populations. International research begun in 2010 showed that boiling potatoes for eight minutes improves their electrical output, as does placing slices of potatoes between multiple copper and zinc plates. Boiled and chopped
plantain pith (stem) is also suitable, according to Sri Lankan researchers.
Instead of fruit, liquids in various containers can be used. Household vinegar (
acetic acid
Acetic acid , systematically named ethanoic acid , is an acidic, colourless liquid and organic compound with the chemical formula (also written as , , or ). Vinegar is at least 4% acetic acid by volume, making acetic acid the main component ...
) works well.
Sauerkraut
Sauerkraut (; , "sour cabbage") is finely cut raw cabbage that has been fermented by various lactic acid bacteria. It has a long shelf life and a distinctive sour flavor, both of which result from the lactic acid formed when the bacteria ferme ...
(
lactic acid
Lactic acid is an organic acid. It has a molecular formula . It is white in the solid state and it is miscible with water. When in the dissolved state, it forms a colorless solution. Production includes both artificial synthesis as well as natu ...
) was featured in one episode of the US television program ''
Head Rush'' (an offshoot of the ''
MythBusters
''MythBusters'' is a science entertainment television program, developed by Peter Rees and produced by Australia's Beyond Television Productions. The series premiered on the Discovery Channel on January 23, 2003. It was broadcast internatio ...
'' program). The sauerkraut had been canned, and became the electrolyte while the can itself was one of the electrodes.
Zinc and copper electrodes are reasonably safe and easy to obtain. Other metals such as lead, iron, magnesium, etc., can be studied as well; they yield different voltages than the zinc/copper pair. In particular, magnesium/copper electrodes can generate voltages as large as 1.6 V in lemon cells. This voltage is larger than obtainable using zinc/copper cells. It is comparable to that of standard household batteries (1.5 V), which is useful in powering devices with a single cell instead of using cells in series.
Learning outcomes
For the youngest pupils, about ages 5–9, the educational goal is utilitarian:
batteries are devices that can power other devices, as long as they are connected by a conductive material. Batteries are components in electrical circuits; hooking a single wire between a battery and a light bulb will not power the bulb.
For children in the age range 10−13, batteries are used to illustrate the connection between chemistry and electricity as well as to deepen the circuit concept for electricity. The fact that different chemical elements such as copper and zinc are used can be placed in the larger context that the elements do not disappear or break down when they undergo chemical reactions.
For older pupils and for college students, batteries serve to illustrate the principles of oxidation-reduction reactions.
Students can discover that two identical electrodes yield no voltage and that different pairs of metals (beyond copper and zinc) yield different voltages. The voltages and currents from series and parallel combinations of the batteries can be examined.
The current that is output by the battery through a meter will depend on the size of the electrodes, how far the electrodes are inserted into the fruit, and how close to each other the electrodes are placed; the voltage is fairly independent of these details of the electrodes.
Chemistry
![ZnCuVoltaicCell](https://upload.wikimedia.org/wikipedia/commons/b/bb/ZnCuVoltaicCell.svg)
Most textbooks present the following model for the chemical reactions of a lemon battery.
When the cell is providing an electric current through an external circuit, the metallic zinc at the surface of the zinc electrode is dissolving into the solution. Zinc atoms dissolve into the liquid electrolyte as electrically charged
ions
An ion () is an atom or molecule with a net electrical charge.
The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conven ...
(Zn
2+), leaving 2 negatively charged
electron
The electron ( or ) is a subatomic particle with a negative one elementary electric charge. Electrons belong to the first generation of the lepton particle family,
and are generally thought to be elementary particles because they have no kn ...
s (e
−) behind in the metal:
This reaction is called
oxidation
Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or a d ...
. While zinc is entering the electrolyte, two positively charged
hydrogen
Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic, an ...
ions (H
+) from the electrolyte combine with two electrons at the copper electrode's surface and form an uncharged hydrogen molecule (H
2):
This reaction is called reduction. The electrons used in the copper to form the molecules of hydrogen are transferred from the zinc through an external wire connecting between the copper and the zinc. The hydrogen molecules formed on the surface of the copper by the reduction reaction ultimately bubble away as hydrogen gas.
Experiment results
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. Goodisman excludes this reaction as being inconsistent with the experiments, and notes that the correct chemistry, which involves the evolution of hydrogen at the copper electrode but also can use silver instead of copper, has been known for many years.
Most of the detailed predictions of the model apply to the battery's voltage that is measured directly by a meter; nothing else is connected to the battery. When the electrolyte was modified by adding
zinc sulfate
Zinc sulfate is an inorganic compound. It is used as a dietary supplement to treat zinc deficiency and to prevent the condition in those at high risk. Side effects of excess supplementation may include abdominal pain, vomiting, headache, and ti ...
(ZnSO
4), the voltage from the cell was reduced as predicted using the
Nernst equation
In electrochemistry, the Nernst equation is a Thermodynamics#Chemical thermodynamics, chemical thermodynamical relationship that permits the calculation of the reduction potential of a reaction (half-cell or electrochemical cell, full cell reacti ...
for the model. The Nernst equation essentially says how much the voltage drops as more zinc sulfate is added. The addition of copper sulfate (CuSO
4) did not affect the voltage. This result is consistent with the fact that copper atoms from the electrode are not involved in the chemical reaction model for the cell.
When the battery is hooked up to an external circuit and a significant electric current is flowing, the zinc electrode loses mass, as predicted by the zinc oxidation reaction above. Similarly, hydrogen gas evolves as bubbles from the copper electrode. Finally, the voltage from the cell depended upon the acidity of the electrolyte, as measured by its pH; decreasing acidity (and increasing pH) causes the voltage to fall. This effect is also predicted by the Nernst equation; the particular acid that was used (citric, hydrochloric, sulfuric, etc.) does not affect the voltage except through the pH value.
The Nernst equation prediction failed for strongly acid electrolytes (pH < 3.4), when the zinc electrode dissolves into the electrolyte even when the battery is not providing any current to a circuit. The two oxidation-reduction reactions listed above only occur when electrical charge can be transported through the external circuit. The additional, open-circuit reaction can be observed by the formation of bubbles at the zinc electrode under open-circuit. This effect ultimately limited the voltage of the cells to 1.0 V near room temperature at the highest levels of acidity.
Energy source
The energy comes from the chemical change in the zinc when it dissolves into the acid. The energy does not come from the lemon or potato. The zinc is
oxidized
Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or a d ...
inside the lemon, exchanging some of its electrons with the acid in order to reach a lower energy state, and the energy released provides the power.
In current practice, zinc is produced by
electrowinning
Electrowinning, also called electroextraction, is the electrodeposition of metals from their ores that have been put in solution via a process commonly referred to as leaching. Electrorefining uses a similar process to remove impurities from a ...
of
zinc sulfate
Zinc sulfate is an inorganic compound. It is used as a dietary supplement to treat zinc deficiency and to prevent the condition in those at high risk. Side effects of excess supplementation may include abdominal pain, vomiting, headache, and ti ...
or pyrometallurgical reduction of zinc with carbon, which requires an energy input. The energy produced in the lemon battery comes from reversing this reaction, recovering some of the energy input during the zinc production.
Smee cell
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. While copper electrodes like those in lemon batteries were sometimes used, in 1840
Alfred Smee
Alfred Smee FRS, FRCS (18 June 1818, Camberwell – 11 January 1877, Finsbury Circus) was an English surgeon, chemist, metallurgist, electrical researcher and inventor. He was also an orchid enthusiast.
Born the second son of William Smee, acc ...
invented a refined version of this cell that used silver with a rough
platinum
Platinum is a chemical element with the symbol Pt and atomic number 78. It is a dense, malleable, ductile, highly unreactive, precious, silverish-white transition metal. Its name originates from Spanish , a diminutive of "silver".
Platinu ...
coating instead of a copper electrode.
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".
The roughened, "platinized" surface speeds up the bubbling of the hydrogen gas, and increases the current from the cell. Unlike the zinc electrode, the copper or platinized silver electrodes are not consumed by using the battery, and the details of this electrode do not affect the cell's voltage. The Smee cell was convenient for
electrotyping
Electrotyping (also galvanoplasty) is a chemical method for forming metal parts that exactly reproduce a model. The method was invented by Moritz von Jacobi
Moritz Hermann or Boris Semyonovich (von) Jacobi (russian: Борис Семёнови ...
, which produced copper plates for letterpress printing of newspapers and books, and also statues and other metallic objects.
The Smee cell used
amalgamated zinc instead of pure zinc; the surface of amalgamated zinc has been treated with
mercury
Mercury commonly refers to:
* Mercury (planet), the nearest planet to the Sun
* Mercury (element), a metallic chemical element with the symbol Hg
* Mercury (mythology), a Roman god
Mercury or The Mercury may also refer to:
Companies
* Merc ...
.
Apparently amalgamated zinc was less prone to degradation by an acidic solution than is pure zinc.
Amalgamated zinc and plain zinc electrodes give essentially the same voltage when the zinc is pure.
[The standard electrode potential is 0.76 V for both pure zinc and for amalgamated zinc. See .] With the imperfectly refined zinc in 19th century laboratories they typically gave different voltages.
In popular culture
*In the video game ''
Portal 2
''Portal 2'' is a 2011 puzzle-platform video game developed by Valve Corporation, Valve for Windows, Mac OS X, Linux, PlayStation 3, and Xbox 360. The digital PC version is distributed online by Valve's Steam (service), Steam service, while al ...
'', antagonist
GLaDOS
GLaDOS (Genetic Lifeform and Disk Operating System) is a fictional artificial intelligence, artificially superintelligent computer, computer system from the video game series ''Portal (video game series), Portal''. GLaDOS later appeared in ''Th ...
was embedded into a potato-battery-run computer for a significant part of the game.
*In ''
The Big Bang Theory
''The Big Bang Theory'' is an American television sitcom created by Chuck Lorre and Bill Prady, both of whom served as executive producers on the series, along with Steven Molaro, all of whom also served as head writers. It premiered on CBS ...
'' Season 6 episode "The Proton Resurgence", Leonard and Sheldon's childhood hero Professor Proton (
Bob Newhart
George Robert Newhart (born September 5, 1929) is an American actor and comedian. He is known for his deadpan and slightly stammering delivery style. Newhart came to prominence in 1960 when his album of comedic monologues, ''The Button-Down Mi ...
) attempts to show the group a potato battery, which amazes Penny.
*In the ''
Bones
A bone is a rigid organ that constitutes part of the skeleton in most vertebrate animals. Bones protect the various other organs of the body, produce red and white blood cells, store minerals, provide structure and support for the body, an ...
'' Season 6 episode "The Blackout in the Blizzard", Angela and the other "squints" build a massive potato battery array in an attempt to power a cell phone. Illustrating the pathetically low output of such a system, it is successful for only a handful of seconds while using dozens of potatoes.
*In the episode "
Lemons
The lemon (''Citrus limon'') is a species of small evergreen trees in the flowering plant family Rutaceae, native to Asia, primarily Northeast India (Assam), Northern Myanmar or China.
The tree's ellipsoidal yellow fruit is used for culina ...
" of the television program ''
Red Dwarf
''Red Dwarf'' is a British science fiction comedy franchise created by Rob Grant and Doug Naylor, which primarily consists of a television sitcom that aired on BBC Two between 1988 and 1999, and on Dave since 2009, gaining a cult following. T ...
'' (
tenth series (Series X)), the crew travel 4,000 miles from
Britain
Britain most often refers to:
* The United Kingdom, a sovereign state in Europe comprising the island of Great Britain, the north-eastern part of the island of Ireland and many smaller islands
* Great Britain, the largest island in the United King ...
to
India
India, officially the Republic of India (Hindi: ), is a country in South Asia. It is the seventh-largest country by area, the second-most populous country, and the most populous democracy in the world. Bounded by the Indian Ocean on the so ...
in 23 AD in order to get lemons to build a lemon battery to power up their
time machine
Time travel is the concept of movement between certain points in time, analogous to movement between different points in space by an object or a person, typically with the use of a hypothetical device known as a time machine. Time travel is a w ...
's returner remote.
*In the sixth episode of the final season of ''
Mystery Science Theater 3000
''Mystery Science Theater 3000'' (abbreviated as ''MST3K'') is an American science fiction comedy film review television series created by Joel Hodgson. The show premiered on KTMA-TV (now WUCW) in Minneapolis, Minnesota, on November 24, 1988. ...
'', the main villain
Pearl Forrester
Pearl Forrester is a fictional character on '' Mystery Science Theater 3000'', and is played by Mary Jo Pehl. Pearl is the mother of Dr. Clayton Forrester ( Trace Beaulieu). Initially devised as a guest character, Pearl became a supporting charac ...
tried taking over the world using potato batteries, only for her plans to be ruined by
Professor Bobo
Professor Bobo is a fictional character who appeared in the final three seasons of ''Mystery Science Theater 3000'', a comedy television series that mocks B-movies. Played by Kevin Murphy (who also voiced and operated robot Tom Servo on the show) ...
.
*In ''
NCIS'' Season 7 episode 8, "Power Down", Abby Sciuto uses lemons as a power source for her stereo when she runs out of batteries during a blackout.
*In ''
Magnum P.I.
''Magnum, P.I.'' is an American crime drama television series starring Tom Selleck as Thomas Magnum, a private investigator (P.I.) living on Oahu, Hawaii. The series ran from December 11, 1980 to May 8, 1988 during its first-run broadcast on th ...
'', Season 3, episode 2, "Easy Money", Magnum uses a lemon battery to charge a walkie-talkie.
*In
Terry Pratchett
Sir Terence David John Pratchett (28 April 1948 – 12 March 2015) was an English humourist, satirist, and author of fantasy novels, especially comical works. He is best known for his ''Discworld'' series of 41 novels.
Pratchett's first nov ...
and
Stephen Baxter's
''The Long Earth'', the devices used to step from one universe to another appear to be powered by potato batteries.
*In ''
Anne with an E
''Anne with an E'' (initially titled ''Anne'' for its first season within Canada) is a Canadian television series loosely Literary adaptation, adapted from Lucy Maud Montgomery's 1908 classic work of children's literature, ''Anne of Green Gables' ...
'' Season 2 episode 10, "The Growing Good of the World," Anne and her classmates use potato batteries to prove to their town how much they've learned from their new teacher's unconventional teaching methods.
See also
*
List of battery types
This list is a summary of notable electric battery types composed of one or more electrochemical cells. Three lists are provided in the table. The primary (non-rechargeable) and secondary (rechargeable) cell lists are lists of battery chemistry ...
*
Alessandro Volta
Alessandro Giuseppe Antonio Anastasio Volta (, ; 18 February 1745 – 5 March 1827) was an Italian physicist, chemist and lay Catholic who was a pioneer of electricity and power who is credited as the inventor of the electric battery and the ...
*
Electrochemical cell
An electrochemical cell is a device capable of either generating electrical energy from chemical reactions or using electrical energy to cause chemical reactions. The electrochemical cells which generate an electric current are called voltaic o ...
*
Galvanic cell
A galvanic cell or voltaic cell, named after the scientists Luigi Galvani and Alessandro Volta, respectively, is an electrochemical cell in which an electric current is generated from spontaneous Oxidation-Reduction reactions. A common apparatus ...
*
Galvanic corrosion
Galvanic corrosion (also called bimetallic corrosion or dissimilar metal corrosion) is an electrochemical process in which one metal corrodes preferentially when it is in electrical contact with another, in the presence of an electrolyte. A sim ...
*
Lasagna cell
*
Penny battery
References
Further reading
* Description of an acid cell with zinc & copper electrodes, including a JAVA-based animation. The animation shows zinc dissolving into the electrolyte, electrons flowing from the zinc to the copper electrodes, and little hydrogen bubbles coming off the copper electrode. The animation also suggests that a single cell can light an LED, which is not possible for LEDs that emit visible light.
* Online preview only.
External links
Lemon Battery video Cool and fun animated video explaining in great detail how a lemon battery works from the inside.
Orange battery video The orange battery powers an inexpensive digital watch.
* . Three potato cells in series power a calculator.
{{DEFAULTSORT:Lemon Battery
Disposable batteries
Biodegradable materials