Friday, December 3, 2010

lemon battery

Oh boy, did we ever have fun with our Science Fridays group today!! Our continued exploration of acids (starting with making cabbage juice pH indicator, which led to us investigating what an acid actually does, which made us wonder what we can do with an acid) led us today to create an actual working battery from one of the acids we've been working with right along -- lemon juice! Here's how it went (we mostly just let the kids experience what was happening, but the pictures won't make much sense without a bit more explanation from me!):

We started with a little review of what happened with our corrosion experiment from last session (2 weeks ago). We got some rust on the steel wool that was left sitting in water. But the steel wool that was left sitting in acid -- it completely disintegrated! There was nothing left but some black crud at the bottom of the cup, and a whole bunch of orange colored liquid. The water (a good electrolyte) caused the particles that made up the steel wool (the atoms) to start coming apart. But the acid (a much better electrolyte) caused those particles to come apart even faster. And as those atoms come apart, they release energy (and some of that energy is electrical energy, as the electrons move through the electrolyte).

So we set out to measure that energy. We introduced some metal substances to our acid electrolyte (lemon juice, handily contained inside a lemon!). We inserted a penny (must be dated prior to 1982 so that there's enough copper in it to work) in one side of the lemon, and a zinc-plated nail in the other. The electrolyte causes both the copper and the zinc to start breaking down, and the released particles (electrons) move from the zinc (becoming the negative) to the copper (becoming the positive).

J tests out his battery on the volt-meter, to see if there is a registrable charge. It read about 0.56 volts. It was working! He was pretty psyched.

Zoo Boy gets ready to test his lemon:

Now that we know that our lemon batteries are producing a charge, is it enough to light up an LED light?

Testing proves no. So what can we do to boost the power??

One answer is to use a different metal (aluminum, as seen above in a later experiment from us Moms who just couldn't get enough of this stuff) that creates a stronger current (releases more electrons in the electrolyte).

But another answer is to join several batteries together in series. Two batteries didn't do it, three batteries didn't either. By the time we hit four batteries, we were producing a charge of over 2 volts, according to the volt-meter. But was it enough to light the LED?

(Look closely, that little red glow next to the middle lemon is the fruit of all their labor.)

The kids were great, they worked really hard, enthusiastic and totally absorbed, for almost an hour on the batteries, and just as quickly lost interest once the bulb lit up. We adults went on to try out different metals and different acids (we built a vinegar battery in a baby food jar as well), while the kids played rambunctiously in the other room. That's the best part about this group -- nobody is interested in pushing more learning on these kids than they are ready to absorb. Of course, it doesn't stop us grown-ups from continuing to feed our passion for learning!! And that's what's important here -- feeding the passion, not forcing content. Ideally, shouldn't all learning be like that?

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