Martin Sneath, age 12, of Oakville, Ont., Canada, for his question:
What are ohms?
Ohms, volts and amperes are units for measuring different aspects of electricity. Each unit was named for a man who mastered one of the steps in taming electric power, and Each man was from a different country and tackled a different factor in a stupendous problem.
Peop1e of the 18th and 19th centuries were coaxed and challenged by the mysteries of electricity. In the 1790s, Galvani of Italy noted that the leg of a laboratory frog twitched when touched with two metals at the same time. Volta of Italy saw that different metals created electricity, and he made a battery that proved it.
Oersted of Denmark noted that a compass need1e reacted to electrical wires. Ampere of France saw that the current created magnetism and made a working magnet of coiled electrical wire. George Simon Ohm of Germany observed the facts then known about electricity and added a sound idea of his own.
Our volt unit of electrical pressure was named for Volta, and WE know that voltage is the pressure that generates current in a wire circuit. Our ampere unit of electric current was named for ampere. We know that current is electrons in motion, hopping from atom to atom in the wires. We also know that all materials resist this electron motion to some extent. Copper is a good conductor with little resistance to block the flow of electricity. Glass is an insulator with strong resistance to moving electrons.
Ohm, the 19th century physics teacher did not know all these facts, but he saw an odd relationship between the voltage, the amperes and the wires of an electrical circuit. He saw that resistance varied with the type of metal and the length and thickness of the wires, and he figured out the precise laws of this electrical resistance.
Ohm saw that voltage was the force behind both the current and the resistance, and, therefore, the resistance must equal the volts divided by the amperes. His law also says that if the resistance stays the same, twice as much voltage must generate twice as much current. The ohm unit of electrical resistance was named in his honor.
The standard ohm unit was internationally approved in 1893, almost 40 years after his death. It is the electrical resistance_produced in exactly 106.3 centimeters of mercury wire. Across section of the wire must have an area of one square millimeter, no more and no less. The equipment must not be a fraction above or below 0 degrees centigrade.