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Science Geek Assistance, Please!

So Dan abducted me to watch a demonstration from a trace minerals company today. The guy did something that he said we were all supposed to have done in science class in school ... something that Rob once said he would do with me: namely, he stuck something into a potato and made a light bulb light up.

Now, actually, I think the thing Rob said he'd do with me had something to do with grinding something pencil sharpener-esque and making a lightbulb light up ... I forget exactly, but I know there was a lightbulb involved. At any rate, I didn't want to seem like a giant dummy in the meeting, so here's my big question:

How the fuck does that work? I thought it had to do with water completing a circuit, but if that's the case, then why did the lightbulb light up with the potato and the tomato, but not the orange or the apple?

Man, where the hell was I when they taught science? 'cause this stuff all seems really cool and like the kind of stuff I would dig, only I don't remember ever experiencing any of it in school.

Comments

( 4 comments — Leave a comment )
qthebrave
Nov. 10th, 2005 09:34 pm (UTC)
I'm by no means a science geek, but last summer I tried this experiment with a lemon. I couldn't get it to work, unfortunately, but I read up on why it works. My understanding is that it's the acid in the fruit/vegetable/whatever that makes it work -- it creates a chemical reaction with the wire and that creates some energy -- so the fruit/vegetable acts like a battery.

Here's info: http://van.hep.uiuc.edu/van/qa/section/Electricity_and_Magnets/Homemade_Batteries/906652432.htm

(google "potato battery" or "lemon battery")

I don't know why the orange or the apple don't work, but I suspect it's that the acidity isn't right to create the reaction.
unixd0rk
Nov. 11th, 2005 12:14 am (UTC)
i had mentioned the experiment which used a hand-cranked generator and a lightbulb (or bank of bulbs) to show that when you complete the circuit to light the bulbs with the generator, the crank becomes harder to turn.

i'm not too well versed on practical fruit chemistry, but the metal that is used in the probes (the anodes and cathodes) is important in getting the hydrogen ions available in the fruit's acids to produce current.

http://www.unit5.org/christjs/Potato%20Battery.htm

The electrochemistry involved is very similar to other batteries.
http://science.howstuffworks.com/battery5.htm explains what actually goes on in the battery.
hopita
Nov. 11th, 2005 01:29 am (UTC)
But wait -- your "Potato Battery" link says that you can use an orange, so now I'm even more confused, because the orange totally didn't work when the guy did that today.
unixd0rk
Nov. 11th, 2005 02:07 am (UTC)
well, that little clock requires perhaps about 1/100th of the power that any lightbulb would. it *might* have powered an LED, similar to your friend's icon up there. LEDs are way more efficient than incandescent bulbs.

...also, since it depends on the chemistry of the fruit, perhaps it was just a "bad orange".
( 4 comments — Leave a comment )

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