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A light switch is a switch, commonly used to operate electric lights, hardwired equipment, or electrical outlets. There are two basic types of electric house light switch: toggle and push (strictly, push to change).
A typical toggle switch has a `toggle` that can be moved in one of two possible positions, up or down which corresponds to `on` and `off` state. In contrast, a push switch changes its state each time it is pushed.
Working
The operation of the switch is simple. When the switch is in open state, no current flows through it. But when the switch is closed, the current starts flowing through it and passes through the circuit connected to it.
Generally, home light switches, being in reality a metal or plastic box with a switch in it, commonly have switch plate covers called wall plates. These are usually plastic, or ceramic, and are there to prevent accidental electrocution, and match with the style fo the room.
A dimmer switch is a kind of light switch that can be used to make the light dim, or brighten the light continuously. More sophisticated methods use a form of pulse width modulation, stopping current flow completely for a fraction of a second and allowing it to flow freely for other periods.
Design
There hasn`t been a significant change in the design (as far as working is concerned) of switches. For example, the dimensions, mechanical designs, and even the general appearance of light switches has hardly changed. Although manufacturers have introduced various new forms and styles, the most part decoration and fashion concerns are limited to the faceplates. In fact, the "modern" dimmer switch with knob is at least four decades old, and even in the newest construction the familiar toggle and rocker switch appearances continue to dominate.
Downsides
A switch is most vulnerable when the contacts are opening or closing.
Reaction of the switch to the `closed` and `open` Conditions
When the switch is closed, the following changes occur in the switch:
-The resistance of the switch changes from nearly infinite to nearly zero.
-At zero resistance, there is no voltage drop and no power is dissipated.
When the switch is open, the following changes occur in the switch:
-The resistance of the switch changes from nearly zero to infinity
-At infinite resistance, no current flows and no power is dissipated.
However regarless of these condition, when the switch changes state, there is a brief instant of partial contact when resistance is neither zero nor infinite and power is dissipated. During that transition the contacts heat up. If the heating is excessive, the contacts can be damaged or even weld themselves closed.
Thus while manufacturing a switch, the transition parameter is into consideration. This kind of design ensures the smooth transition between effectively infinite resistance and effective zero resistance
This is achieved by the initial operation of the switch lever mechanism storing potential energy, usually as stress in a spring. When sufficient energy is stored, the mechanism in the switch "breaks over" driving the contacts through the transition from open to close, or close to open, without further input the switch operator.
In addition, during the transition when the contact is broken there is an additional issue that if an inductive load is being switched, the stored energy in the inductor is dissipated as an arc within the switch, prolonging the transition and worsening the heating effect on the contacts. Thus switches are commonly rated by the current they are designed to break, as this is the most stringent constraint.
In order to prevent contact corrosion, a switch is usually designed to have a wipe action so that the contact corrosion is cleaned off the area of the contact that forms the low resistance path when the switch is closed. In addition, the design is made in such a way that the initial point of contact, and majority of the contact corrosion, occurs at a sacrificial part of the contact, rather than the face which comes in contact when the switch is fully closed. Depending on the switch rating and price, the contact area of the switch is often a sophisticated construction of brass contact, silver contact button, and plated finish to minimize the amount of contact corrosion and thus extend the life of the switch.
To make a switch safe, durable, and reliable, it must be designed so that the contacts are held firmly together under positive force when the switch is closed. This action should take place irrespective the way the person operating the switch manipulates it.
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