This week's experiment comes from a sudden cluster of e-mails asking about producing electricity with various fruits and vegetables. This is one of the experiments that pops up quite often in science books, and it is also one of the experiments that seldom seems to work like the books say. To try it successfully, you will need:
* various fruits
* copper wire, paper clips, keys, or other pieces of metal
* headphones from a radio, tape player, etc.
If you pick up almost any book of electricity experiments for kids, you will find instructions for making a battery from a lemon or other fruit. First, what you are making is not a battery. Instead we are going to construct an electric cell. To have a battery, you need two or more cells wired together. Technically, the 1.5 volt batteries (AA, AAA, C and D) are really cells. 6 and 9 volt batteries, are really batteries. You can even figure out how many cells are in each one. Each of the cells in these batteries can produce 1.5 volts. Two cells added together would produce 3 volts. For 6 volts, you need 4 cells. For nine volts, you need 6 cells. How many cells would you need for a 12 volt car battery?
For my cell, I used a potato, but you can use a lemon, apple, or other fruits and vegetables. You will also need two objects made of different metals. I used a nail and a piece of copper wire. Stick one piece of metal into the potato. About an inch away, stick the other piece of metal into the potato. You now have two different metals connected by the juice in the potato. This forms a simple electric cell, which can produce about one half of a volt.
How are we going to tell if the cell is working? Some books suggest that you connect this cell to a flashlight bulb. The problem is that every flashlight bulb that I have ever seen needs a lot more voltage (push) and amperage (amount of electricity) than you can get from your potato cell. Other books suggest touching the two metal objects to the tip of your tongue, but I have never been able to get that to work either.
You can detect the electricity by connecting the cell to an electric volt meter, if you have one. If you don't, then you can easily detect the electricity with headphones or an earplug from a radio, CD player, etc. Don't worry, we won't hurt the headphones. If you look at the plug from the headphones, you will see that the metal part is made of two or three sections. Put on the headphones. Touch one piece of metal to one section of the headphones and the other piece of metal to one of the other sections. If you listen carefully, you should hear a small click. If the plug has three sections, then you may have to try touching different sections to hear the click.
Your headphone works by converting tiny electric signals from your radio into sounds. The electricity from your potato cell produces the click you hear. Every time you connect and disconnect the metal pieces from the plug, you get another click. You can even try using different kinds of fruit and different pieces of metal, to see which produces the loudest click. The better your cell works, the louder the click will be.