Supplies: Copper Plate
A Human Battery
In a nutshell, a battery uses a chemical reaction to produce an electrical current.
Mount the copper and aluminum metal plates to two separate pieces of wood. Connect one plate to one of the DC microammeter's terminals using an alligator clip and the hookup wire. Connect the other plate to the second terminal. A DC microammeter, which is an instrument that measures the electric current in a circuit, can be purchased from your local Radio Shack store. Now place one hand on each plate.
You should see an electric current generated on the meter. If you don't see a reading then simply reverse the connections. If you still don't see a reading then you may need to clean the metal plates (or get a pair of better reading glasses).
When you place your hands on the metal plates, a thin film of sweat on your hands acts just like the acid in a battery, producing a chemical reaction with the copper plate and a chemical reaction with the aluminum plate. Your hand actually takes negatively charged electrons away from the copper plate (leaving positive charges behind) and gives electrons to the aluminum plate (causing it to become negatively charged).
Wet both hands. Once again, place one hand on each plate.
Metals are very efficient at this electrical current we have created. Your body resists the flow of current (through the skin). When you wet your hands you greatly decrease the resistance and thus increase the current giving you a higher reading on the meter.
Parent's Note. Batterys have actually been around a lot longer than you'd think. The first practical battery was probably developed by Count Alessandro Volta, an Italian scientist, in the late 1790's. Volta's invention became known as a voltaic pile. It consisted of a stack of pairs of silver and zinc disks. The pairs were separated from one another by disks of cardboard moistened with a salt solution.
In 1836, John F. Daniell, an English chemist, introduced a more efficient primary cell. The Daniell cell had two liquid electrolytes and produced a steadier current than Volta's device. In 1859, the French physicist Gaston Plante invented the first secondary battery, the lead-acid storage battery. During the 1860's, another French scientist, Georges Leclanche, invented a type of primary cell from which the modern dry cell was developed.
Through the years, scientists have designed smaller but increasingly powerful batteries for the growing number of portable electric devices. For example, a lithium cell is so tiny that it is often called a button battery. But it produces voltages higher than any other single cell. It uses lithium metal as the negative electrode and any one of several oxidizing agents as the positive electrode. Lithium cells are used mainly in calculators, cameras, pacemakers, and watches.
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X - 4 = 3
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