In the simplest case, a switch has two conductive pieces, often metal, called contacts, connected to an external circuit, that touch to complete (make) the circuit, and separate to open (break) the circuit. The contact material is chosen for its resistance to corrosion, because most metals form insulating oxides that would prevent the switch from working. Contact materials are also chosen on the basis of electrical conductivity, hardness (resistance to abrasive wear), mechanical strength, low cost and low toxicity.
Sometimes the contacts are plated with noble metals. They may be designed to wipe against each other to clean off any contamination. Nonmetallic conductors, such as conductive plastic, are sometimes used. To prevent the formation of insulating oxides, a minimum wetting current may be specified for a given switch design.
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Famous quotes containing the word contacts:
“The modern nose, like the modern eye, has developed a sort of microscopic, intercellular intensity which makes our human contacts painful and revolting.”
—Marshall McLuhan (1911–1980)
“In all our contacts it is probably the sense of being really needed and wanted which gives us the greatest satisfaction and creates the most lasting bond.”
—Eleanor Roosevelt (1884–1962)
“Living more lives than one, knowing people of all classes, all shades of opinion, monarchists, republicans, socialists, anarchists, has had a salutary effect on my mind. If every year of my life, every month of the year, I had lived with reformers and crusaders I should be, by this time, a fanatic. As it is I have had such varied things to do, I have had so many different contacts that I am not even very much of a crank.”
—Rheta Childe Dorr (1866–1948)