More science
and technology projects from Hila Science
(geodesic domes, sundials,
kites, trebuchets......)
Follow these links to video clips supporting this project:
Introduction to Electricity - Hila Video on Youtube
Build a Lemon Battery - Hila Video on Youtube
Creating a battery from a lemon is a common project in many
science text books. Successfully creating one of these devices is not
easy.
Batteries consist of two different metals
suspended in an acidic solution. Copper and Zinc work well as the metals
and the citric acid content of a lemon will provide the acidic solution.
Batteries like this will not be able to run a motor or
energize most light bulbs. It is possible to produce a dim glow from an
LED.
The picture at the top of this page shows a basic lemon battery, a lemon, copper penny and zinc coated nail.
The lemon: A large, fresh, "juicy" lemon works
best.
The nail: Galvanized nails
are coated in zinc. I used a 2" galvanized common nail.
The penny: Any copper coin will work. (Canadian pennies
from 1960 - 2001 all worked)
Creating the battery: Insert a penny into a cut
on one side of the lemon. Push a galvanized nail into the other side of
the lemon.
The nail and penny must not touch.
This is a single cell of a battery. The zinc nail and
the copper penny are called electrodes. The lemon juice is called
electrolyte.
All batteries have a
"+" and "-" terminal. Electric current is a flow of atomic
particles called electrons. Certain materials ,
called conductors, allow electrons to flow through them.
Most metals (copper, iron) are good conductors of electricity. Electrons will
flow from the "-" electrode of a battery, through a conductor, towards the
"+" electrode of a battery. Volts (voltage) is a measure of
the force moving the electrons. (High voltage is dangerous!)
I have connected a volt meter to our single cell lemon
battery. The meter tells us this lemon battery is creating a voltage of 0.906
volts.
Unfortunately this battery will not produce
enough current (flowing electrons) to light a bulb.
To solve this problem we can combine battery cells to create higher voltages. Building more lemon batteries and connecting them with a metal wire from "+" to "-" adds the voltage from each cell.
The two lemon batteries above, combine to produce a voltage of 1.788 volts. This combination still does not create enough current to light a small bulb. Note the red wire connecting the batteries is joined from "+" (penny) to "-" (galvanized nail).
Four lemon batteries create a voltage of 3.50 volts. We
should be able to light up a small device like an LED (Light Emitting
Diode).
Note the connecting wires go from "+" to "-"
on each battery.
LED
To turn on an LED you must determine the "+" and "-"
connections. If you look closely at the red plastic base of an LED you
will notice a "flat" spot (indicated by arrow above). The wire that comes
out beside the flat spot must connect to the "-" side of a battery, the other
wire to the "+" side.
Important information about LEDs: LEDs are
designed to work at very low voltages (~ 2V) and low currents. They will
be damaged if connected to batteries rated at over 2 volts. LEDs require
resistors to control current when used with batteries rated at over 2
volts. Lemon batteries produce low current. It is OK to connect an LED to
a lemon battery.
In the above image, electrons flow from the "-" (nail) end of our lemon battery through the LED (making it glow) then back to the "+" (penny) end of the battery. This is an electronic circuit. The LED glows dimly with this configuration.
The quality of the copper and zinc can be a problem for a
battery like this. Pennies in particular are rarely pure copper.
Try substituting a length of 14 gauge copper wire (common
house wire) for the penny. Experiment with different lengths and
configurations of electrodes. Other sources of zinc and copper may be
found in the plumbing supply department of a hardware store.
The first battery was created in 1799 by Alessandro Volta . Today batteries provide the power for an amazing variety of devices, everything from flashlights to robots, computers, satellites and cars. Inventors and researchers continue to improve the battery, designing batteries that last longer and that are more friendly to our environment.
Understanding how batteries actually work requires a knowledge of chemistry. The most important factor in battery design is the electrical relationship between the two metals used in the battery. Some metals give electrons away while other metals accept extra electrons. Chemists have investigated metals and created an "electric potential" table comparing different metals.
Link to Electric Potential Table
Link to advanced information about batteries.