Jun. 24, 2011

Science Dad on Potatoes and Protocols

by Vince Harriman

Click to enlarge images

Happy Birthday, Rowan!

We had a busy week around here -- Rowan turned three! Beckett, however, was doing his own science projects all week, and, at the last minute, after a long afternoon and evening of parties and cake, asked me what we were going to do for Science Dad. Sheesh! Since Beckett had already been independently working on creating a lemon battery, we decided to see if we could get the battery to function.

Lemon batteries (or potato batteries, or fruit batteries, or any light acid battery...) are generally very easy to make: you start with a light acid source, such as a lemon or potato, add a copper and zinc strip, then connect to a device or multimeter and you've generally got electricity. Do it while half asleep after a long day without re-reading the directions or refreshing yourself on what to do, however...

Beckett had started this experiment on his own on Monday or Tuesday, and, by the time I got home to see it, we were out of vinegar and lemons and he was beginning to cut up clementines and apples. This experiment is something I've done a dozen or so times in my life for various reasons. So, without reading any directions, or thinking much about it, I started doing what Beckett was doing and began poking fruit with strips of metal. I wasn't thinking about how the experiment works, or even how electricity in general works. I was just sticking fruit with pieces of metal.

I've always said that a certain amount of fun should be had when doing science -- in fact, the more fun science is at this age, the more I think sticks with the boys. So we poked and poked and dipped and prodded, but we could not get anything to work. Beckett had also attached the light bulb (a tiny low voltage LED) and digital watch to a regular battery to 'see' if they did in fact work, which may have blown the bulb. Needless to say, after a quite a bit of messing around without any results, the experiment was getting less and less fun, and more and more frustrating.

The complete circuit

The electrical energy of the battery does not come from the potato but, rather, the effect the potato has on the metal strips. As the zinc strips begin to oxidize, they release the (now) extra electrons as the chemical reaction takes place. These electrons accumulate and begin to flow. On the copper side, hydrogen ions form. Electricity flows between the strips!

The first thing to know about this experiment (especially when doing it with kids who are expecting something dramatic) is how very little electrical energy is actually produced. Wikipedia provides a calculation for example of how many lemons would be needed to power a regular flashlight bulb. Assuming a single lemon produces .00027 watts and the bulb needs 2.4 volts and .5 amps, you would need 5000 lemons hooked together to do the work of a single AA battery! Beckett started with a single lemon and got nothing before moving on to poke and prod all the fruit in the house.

It's alive! IT'S ALIVE!

Then I came along to 'help' without refreshing myself on the experiment -- or even remembering how little electricity is produced -- and duplicated all of his mistakes. Which brings me to protocols. Most of the science projects and experiments we do with kids are fairly straightforward. As a parent, I've found that the most important thing I can do is prepare a bit ahead of time. I don't always know the result or outcome, but the more 'homework' I can do, the happier we all are in the end. When we did our paper airplane experiment, for example, the day was chaos! 80 boys and girls folding and flying hundreds of planes and throwing them absolutely everywhere. We had a blast! As we did the experiment, and I watched plane after plane not fly or not fly straight or nose dive, I was very worried about the outcome of the experiment. But we had set up a protocol for folding, flying, and recording, and in the end, the results were textbook perfect. I hadn't known the outcome before, but setting up the experiment properly allowed us to find results amid the fun and chaos.

As we ran out of fruit and turned to the refrigerator for potatoes, I finally read the directions and found out what I was doing wrong. I helped Beckett wire the zinc and copper properly to the watch and we had electricity!

So for all you Science Moms and Science Dads out there, if you are doing an experiment please follow all the directions! Make sure that you follow all safety precautions requested and make sure that you begin the experiment with everything you need where you need it. And make sure you make it fun!

About Vince Harriman

Science Dad, AKA Vince Harriman, is a freelance writer living in Annapolis. His two sons, Beckett-6 and Rowan-2 1/2 ask him 'why' approximately 6,542 times a day.

The views expressed are those of the author and are not necessarily those of Science Friday.

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