For technical evolution purpose this
kind of passive component can be analyzed considering the
fixed and variable resitors. The first resistors used in Electronics
were known as wire-wound resistor, which generally was made
by widing a wire, made of alloys such as the constantanium
or nichrome around on an insulating tube. Continuously variable
resistors, actually known as potentiometer, considering it
was originally used for voltage division by branching a resistor
like the volume control on a radio set, basically consists
a movable contact along a wire wound resistance or toroid
insualting material.
Nowadays the carbon potentiometers are made by applying a
carbon film to a horse shoe plate of sinthetic resin bonded
paper, along which a slide contact which runs by turning a
splindle. Both ends of the horseshoe are silver coated over
the carbon layer for the proper connection in the terminals.
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