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 Switches are used everywhere today both in the home and in business. We use them so often and without thinking that we probably couldn’t even estimate how many times a week we flick a switch on or off. The switch itself is a part of an electrical circuit that controls the flow of current by either stopping the flow or by diverting it onto another route with a different result. The most common type of switch that we see are electromechanical devices. These switches have one ort more electrical contact points. These contacts can be closed meaning that the contact points are touching and allowing the flow of current to continue, or they can be open with the two contact points separated that halts the current flow. The simplest example of a basic switch system would be the everyday light switch.
The contacts within a switch system are two pieces of metal. The choice of which metal is used is based around its corrosion susceptibility. Metals that corrode easily are not used in switches, as the metal oxide that forms on the contacts will interfere with the switch efficiency making it unreliable. The other factors of selection of the material used in creating the contacts for a switch are elements such as their electrical conductivity, their durability, their low cost and how toxic the metal is. The other important part of a switch is of course the actuator, which is the lever or button that we flick to cause the contacts to complete the circuit or to break it. http://en.wikipedia.org/wiki/Switches#Up_or_down
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