Coin Batteries


They say the penny is, or will soon be, obsolete.  I beg to differ.  My kids had a great time sorting, bouncing and stacking pennies for this project.  We even learned a little bit about this humble coin as we figured out the best way to do the experiment.  Using only coins, paper towels and vinegar, your child can make his or her own wet cell, a kind of battery.  

It’s a safe, easy way to experiment with electricity using pennies and other coins as electrodes (which collect charge) and vinegar, lemon juice or salt water as electrolytes (which pass the charge, or electrons, from coin to coin).  Holding this homemade battery between two wet fingers completes the circuit and sends a tingle of electrical current strong enough for your child to feel!  It’s a little complicated, but you can explain that you are making a battery, similar to one in a flashlight, and that the coins are like the two different ends of any battery, with a positive end (+) and a negative end(-).

What you will need:  10 or more pennies, 10 or more non-metal coins (quarters, dimes or nickels), paper towels, vinegar, salt water (optional) and lemon juice (optional)  For simplicity’s sake, I’m going to call the non-copper coins quarters as I describe the experiment, but any of the non-copper coins I suggested may be used!

First, have your child sort the pennies into two piles: pennies made before 1982, and pennies made after 1982.  Keep any pennies made in 1982 in a separate pile. Pennies made before 1982 are 95% copper, those made after 1983 are 97.5% zinc with a thin copper coating.  Pennies made in 1982 could be either zinc or copper.  All pennies will work, if you don’t have enough of one kind or another, since the current travels through the copper surface on the coated ones. 


Pour some vinegar in a bowl.  Have your child cut the paper towels into small squares around a half an inch on each side.  Then, have them soak the paper towel pieces in the vinegar.   Stack ten pennies and ten quarters with a piece of soaked paper towel between each coin (e.g. penny, paper towel, quarter, paper towel, penny, paper towel and so forth.)  Be sure to alternate penny, quarter, penny, quarter!  It works best if the pieces of paper towel aren’t touching each other.  We made ours a little too big, as you can see.  


Finally, have your child wet one fingertip on each hand and hold the pile of coins between those two fingers.  (See photo at top of this post!)  They should feel a slight tingle as the electricity flows between their fingers!  I had to hold the stack for several seconds before I felt anything.

Let your child try other variations on the experiment if they’re interested!  See how well lemon juice works as the electrolyte.   Ask them what vinegar and lemon juice have in common. (They’re both acids!)  Try salt water as the electrolyte. Do the pennies made before 1982 make better batteries than the new zinc pennies?  Have them bounce the copper and zinc pennies on a linoleum surface.  They should make slightly different sounds.  Can they determine whether the 1982 pennies are copper or zinc by the sound they make?  Did the vinegar make the old pennies shiny?  Why? 

Pull out those science notebooks and have them record their results!  They can record their results, draw a coin battery, make a graph of how many pennies they had from different years, or even do some penny rubbings with a pencil!

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