To look at them, switches are simple. Your house, workplace and school each probably have a dozen or more switches built into the walls to turn lights and wall sockets on and off. The most interesting switches, however, are the ones you cannot see. Hidden within ordinary appliances and gadgets are the networks of small switches that power sensors, displays and computers of all types.
Significance
Simply put, no electric circuit can function without a switch. Lamps cannot be turned on at night and off during the day, heating systems cannot keep the temperature at a certain level, and CD players cannot switch tracks. Modern computers use vast arrays of hundreds of thousands of minuscule switches, called transistors, to perform complex calculations in an instant. More than anything else, the size and speed of these ever-smaller, ever-faster switches determines the advance of the digital revolution.
Function
A switch controls the flow of electricity. Most switches simply turn power on and off, but some switches are capable of more subtle control. A dimmer switch, for example, is able to adjust the power level of a lamp to any value between full power and completely off. A transistor switch can also vary the current to nearly any level between all the way on and all the way off. Because of this ability, transistors can be used to amplify music. They take a small electronic wave representing a musical signal and use it to control a larger electronic wave representing a louder musical signal.
Types
The switches on your walls are mechanical switches. They have two pieces of metal inside, each attached to one side of a circuit. When the switch is turned on, the pieces touch and electricity flows through the circuit. When the switch is turned off, the connection is broken and power cannot flow.
A circuit breaker is a special kind of mechanical switch. It stays closed most of the time, but automatically opens when too much current goes through it. The switches that turn on appliances are usually relays. A relay is a small mechanical switch that powers a bigger switch. When you turn on the television, it closes a mechanical switch that generates an electromagnetic field. That field pulls a bigger switch closed, turning on your television. The switches inside computers, cell phones and other pieces of complex electronics are called transistors. A transistor is a bit like a very small, very efficient relay. A small voltage controls a much larger voltage. Transistors can be used in complex arrangements to perform logical processes, amplify sounds and do many other useful things.
Features
Most switches are good at doing one particular sort of task. Mechanical switches and relays are very stable, and can handle a lot of current without wasting much power. They are good for tasks in which you only have to turn something on or off every once in a while. This is why they are used in the main power supplies of appliances, and to control the lighting in your house. Transistors are good switches if you need to be able to turn something on and off very quickly. They have no moving parts, so they can't be damaged by being constantly opened and closed, as mechanical switches and most relays can. They do waste some energy, however, so they really aren't as good as mechanical switches and relays for main power sources.
Potential
One of the biggest obstacles to computers is electromagnetic interference. As tiny transistors send incredible amounts of information back and forth very quickly, the signals start to interfere with each other. This makes it hard to make computers any faster after a certain point. One possible solution is to use fiber-optic circuits and switches. Fiber optics use light instead of electricity; light doesn't have the same interference problems that electricity does. Already, fiber-optic cables can speed up Internet traffic. If computer engineers can develop a fiber-optic version of a transistor, they will be able to make computers much faster and more powerful.
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