Science Buddies: "Ask an Expert"

We are having difficulty getting a stable reading on our multimeter for the Battery that makes Cents experiment. 2 of our ten trials yielded numbers with some consistency with numbers like 0 for two coins, 1.8 for 4 coins, 3.5 for 6 coins and 6.5 for 8 coins. All of the other trials have been too difficult to read with measurements ranging from 70.2 to 0 on every test. The digital numbers just keep going up and down. We are testing millivolts on the DC setting. Help! My little scientist jumped ship after a noble 5 tests, and we have been watching you tube tutorials and running trials all day.

429704 43 - I've never done this experiment, but in reading the procedure, I believe there could be a small issue relative to the size of the piece of paper towel that is used. It might be possible for a 1 cm square (smaller that the diameter of either coin) to allow some of the coins to "short circuit" together, preventing you from getting an accurate reading. I suggest making the papers slightly larger, perhaps just barely covering the penny, and trying that. If a paper is too large, it might droop over and contact another paper. Because the coins have a ridge around the circumference and high points of 'relief' in the images, a potential "short" is possible. Because the larger paper towel covers the penny, you might consider placing a piece of aluminum foil on your table surface to place the first penny on. Use the foil as your electrical contact. Another caution, don't allow the paper to get too wet with the electrolyte. If the electrolyte drips around the edge of a coin, it may "short" out some of the coins. Keep the coins dry except for the moistened paper towel. Assuming the metal compositions of the coins are similar, you should see a constant voltage for a single cell. Multiple cells would display the sum of the voltages developed across each pair. For example, a single cell might be 75 millivolts. A two cell stack would be 150 millivolts, three cells would be 225 millivolts, and so on.

Let us know if this helps.

Rick Marz