This Week's Experiment - #478 Batteries?

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!