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Five or more post-1982 U.S. penniesPiece of 100-grit sandpaperMatboard or thick cardboardSaltVinegarA red LED; high-intensity ones are easier to seeElectrical tapeCup with waterPaper towelOptional: other LEDs of different colors, such as yellow and blue
Make sure the pennies aren’t touching each other.Make sure the cardboard isn’t touching each other.Dry off any liquid that oozes out.
5-Cent Battery
Light an LED with five cents of electricity.
Tools and Materials
Prep
STIR
Make a saturated salt solution by adding salt to water and stirring until it no longer dissolves. Add a splash of vinegar to this solution.
CUT
Cut your cardboard into four 1/2-inch squares, each about the size of a penny.
SOAK
Soak the pieces in the salt-and-vinegar solution.
Once the pieces are thoroughly wet, take them out and place them on a paper towel so they are still damp, but not dripping.
SAND
Use sandpaper to remove the copper from ONE side of each of four pennies. Leave the fifth penny intact.
Sand until you see zinc (shiny silver color) covering the entire face of the coin. This takes some time and effort, so be patient. Try placing the sandpaper on a hard surface and moving the penny instead of the sandpaper.
The "tails" side may be easier to sand because the Lincoln Memorial (or Union Shield) doesn't protrude as far as Lincoln's head.
When you're done, the sanded coins should have a bronze-colored copper side and a silver-colored zinc side.
Build
Build a layer cake of pennies in this order:
Troubleshoot
Test
Connect an LED
Test your battery by connecting your LED. Touch the longer lead to the intact penny on the top and the shorter lead to the bottom of the stack. Make sure that the leads don't touch any other layer.
Did the LED turn on? If not, make sure the LED leads are oriented correctly and use a paper towel to wipe off any excess water from the penny-cardboard stack.
Now collect some data in your notebook.
Table (example)
Number of pennies in stack
Brightness (1-5)
LED color
There are no rows in this table
What’s Going On?
Batteries are devices that convert chemical energy into electrical energy. When two different metals are connected by an electrolyte, a chemical reaction occurs at each metal surface, called electrodes, that either releases or uses electrons. When these electrodes are connected by a wire, electrons will move from one surface to the other, creating an electric current.
Pennies that were made after 1982 have zinc cores that are plated with copper. By sanding off one face of a penny, you create a zinc electrode that can pair with the copper electrode on the face of the next penny. The matboard soaked in salty vinegar water serves as the electrolyte between the two terminals.
Each zinc-matboard-copper stack represents one individual cell. By stacking additional matboards and sanded pennies, you’ve created a battery, which is a series of electrochemical cells. This is also called a voltaic pile, which is named after Alessandro Volta, who created the first battery in 1800 by alternating zinc and copper electrodes with sulfuric acid between them. In Volta’s battery and your penny battery, an oxidation reaction occurs at the zinc electrode that releases electrons and a reduction reaction occurs at the copper electrode that uses them.
With a voltmeter, you can see that each cell can generate over 0.6 volts. The first penny battery you created has four cells. A stack of three cells should generate enough voltage to light a red LED, which usually require around 1.7 volts.
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