The first kind of dimmer switch made use of a variable resistor.
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The first kind of dimmer switch made use of a variable resistor. In this kind of device, a [[semiconductor]] strip is placed between two contact arms--one is stationary, one is adjustable. The semiconductor permits the flow of electricity, but does resit it somewhat. The stationary contact arm is placed at one end of the semiconductive strip, and the adjustable one is permitted to move across it. When the latter arm is placed right near the stationary arm, electricity flows from one arm through a small amount of the semiconductor, and out to the other arm. Since it only passes through a small amount of semiconductor, the power flow is minimally effected. However, when the adjustable arm is moved down the strip, away from the stationary arm, the amount of semiconductor the power must flow through increases. This prevents progressively more electricity from passing through, as the arms separate.<br />
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This simple system is then installed into a switch, where the user can easily move the adjustable arm. The resulting supply is then connected to some device, usually a light bulb.