08/11/08 13:32:21
The Ever-Flowing River
Electrical energy, essential in any modern society, is delivered through metal wires, most commonly made of copper.
Materials like copper that allow electricity to pass through them are called conductors.
An electrical current is caused by the movement of electrons through the wire.
Electrons in the outer layer of atoms in the wire move from atom to atom, creating an electric current.
What causes them to move is an electrical potential difference between different parts of the metal.
This is similar to the way a river flows downhill because of the gravitational potential difference between the top of the hill and the bottom.
As electrons move through a conductor, they bump into its atoms and lose some of their energy.
This can be compared to the way a rocky river bed slows down the water flowing over it.
The lowest temperature possible is minus 273 degrees Celsius(℃), or zero degrees kelvin(K).
In the early 20th century, a Dutch scientist, Heike Onnes, investigated the effect of the temperature of a metal wire on how it conducted electricity.
He found that in a mercury wire at 4.2K (the same as minus 269℃), electricity flowed without losing any energy.
In another experiment using a lead wire at 4K, he started an electric current, removed the source of the current,
and found that the current was still flowing at the same strength a year later.
This could be compared to a river that keeps flowing on a flat surface without the effect of gravity.
Heike Onnes called this state superconductivity, and materials in this state are called superconductors.
Onnes was awarded the Nobel Prize in Physics in 1913.
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