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Krampf #478 Batteries?
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KRA-@aol.com
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Mar 14, 2007 03:51 PST
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Robert Krampf's Experiment of the Week
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This Week's Experiment - #478 Batteries?
Greetings from our home in Jacksonville. Nancy and I had a wonderful week
off. We planted lots of flowers. I also played with the antique 3D camera
that Nancy gave me for Christmas. I managed to get several good stereo pairs
from the first roll of film, and I am now hooked on stereophotography. We
also taped the first 12 Experiment of the Week videos. Omar is editing them
now, and the first couple should be up on my website very soon. I will let you
know when they are online.
I wrote this week's experiment while I was writing an electricity manual for
the Memphis Pink Palace Museum's Suitcase Outreach program. Usually I try to
stick to everyday language instead of using technical terms when I write the
Experiment of the Week. That gets me quite a few email saying that
technically I should use "mass" instead of "weight", "NaCl" instead of salt, and so on.
This week, I am going to get technical to help show you some interesting
things. To try this, you will need:
pliers
a 9 volt battery
battery powered devices around your house
First, look around at some of the things in your house that run on batteries.
What if I told you that some of them really do not run on batteries? It
would be true, but only on a technicality.
The first battery was invented by Alessandro Volta, back in the year 1800.
He found that by using a disc of zinc and a disc of copper with a piece of
cloth soaked in salt water placed between them, he could produce a current of
electricity. You might have seen similar experiments where you stick a piece of
copper and a piece of zinc into a lemon to produce electricity. Volta found
that one cell did not produce much electricity, but by stacking several cells,
he could combine their voltage (which is named after Volta). The more cells
he stacked, the more voltage he got. That stack of cells was the first
battery.
That is where our technicality comes in. Technically, a battery has to have
two or more cells. When you look at AA, AAA, C and D "batteries", you find
that each of them is really a single cell. That means that if you have a
small flashlight that only takes one of these, it runs on a cell, not on a
battery. Of course, if your flashlight uses 2 D cells, then you have a battery,
since the total is 2 cells.
OK, so I am splitting hairs a bit, but there is a good reason. The most
voltage that you can get out of a modern electric cell is 1.5 volts. If you
look at the voltage on AA, AAA, C and D cells, you will find that all of them
produce 1.5 volts (unless they are rechargeable, which usually only produce 1.2
volts) If you find a "battery" that produces more than 1.5 volts, then it
probably really is a battery, containing 2 or more cells.
Now, lets look at our 9 volt battery. Because it produced 9 volts, we can
be pretty sure that it actually is a battery. Before we check, lets do some
math.
Math! Wait a minute! No one said anything about me having to do math!
Well, this is simple math, so I guess it is OK. We are going to calculate how
many cells the battery has. Let's start with 1.5 volts for one cell.
Adding another cell will add the voltages, so we will have 3 volts. If two cells
give us 3 volts then 4 cells should give us 6 volts, and that means that to
get 9 volts we would need six cells.
Let's check and see if that is correct. Look at the top of the 9 volt
battery. It has two electrical contacts on its top. The sides are metal, and
bend inwards to hold the top in place. CAREFULLY use the pliers to bend the
metal sides away from the top. Be very careful, as the metal edge may be
sharp. When you bend the sides enough, you should be able to remove the top.
What do you see inside? 6 small electric cells. They look like AAA cells,
but they are even smaller. Our math was correct.
You can do the same thing with other batteries. What about one of the
large, square, 6 volt lantern batteries? How many cells would it have? Four,
right? Right. If you open one, you will find....four D cells. Most car
batteries are 12 volts. How many cells would that be? Do the math, and then
look at your car battery. You should be able to see evidence that it has 8
cells, which will total to 12 volts.
So you see, there are times when it helps to use the technical jargon. Now
I am off for a bowl of ice cream, which will probably cause me to gain some
mass.
Have a wonder filled week!
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From Robert Krampf's Science Education Company
PO Box 60982
Jacksonville, FL 32236-0982
904-388-6381
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