Editing Potentiometer (section)

== Rheostat ==
{{see also|Liquid rheostat}}
The most common way to vary the resistance in a circuit continuously is to use a '''rheostat'''.<ref>{{Cite book|last=Jhakki|first=Akki|title=Concise Physics Class IX (ICSE)|publisher=Selina Publishers Pvt. Ltd.|year=2020|isbn=9789388594387 |location=New Delhi |pages=189}}</ref> Because of the change in resistance, they can also be used to adjust magnitude of current in a circuit. The word ''rheostat'' was coined in 1843 by Sir [[Charles Wheatstone]],<ref>{{cite journal |last1=Wheatstone |first1=Charles |title=An account of several new Instruments and processes for determining the constants of a voltaic circuit |journal=Philosophical Transactions of the Royal Society of London |date=1843 |volume=133 |pages=303–327 |url=https://www.biodiversitylibrary.org/item/214335#page/353/mode/1up }} 
 From p. 309:  "As the principal use of this instrument is to adjust or regulate the circuit so that any constant degree of force may be obtained, I have called it a Rheostat."</ref> from the Greek {{lang|grc|ῥέος}} ''rheos'' meaning "stream", and -{{lang|grc|στάτης}} -''states'' (from {{lang|grc|ἱστάναι}} ''histanai'', "to set, to cause to stand") meaning "setter, regulating device",<ref>Brian Bowers (ed.), ''Sir Charles Wheatstone FRS: 1802-1875'', IET, 2001 {{ISBN|0-85296-103-0}} pp.104-105</ref><ref>{{cite OED|stat}}</ref><ref>{{LSJ|r(e/os|ῥέος}}, {{LSJ|i(/sthmi|ἱστάναι|ref}}.</ref> which is a two-terminal variable resistor. For low-power applications (less than about 1 watt) a three-terminal potentiometer is often used, with one terminal unconnected or connected to the wiper.

Where the rheostat must be rated for higher power (more than about 1 watt), it may be built with a resistance wire wound around a semi-circular insulator, with the wiper sliding from one turn of the wire to the next. Sometimes a rheostat is made from resistance wire wound on a heat-resisting cylinder, with the slider made from a number of metal fingers that grip lightly onto a small portion of the turns of resistance wire. The "fingers" can be moved along the coil of resistance wire by a sliding knob thus changing the "tapping" point. Wire-wound rheostats made with ratings up to several thousand watts are used in applications such as DC motor drives, electric welding controls, or in the controls for generators. The rating of the rheostat is given with the full resistance value and the allowable power dissipation is proportional to the fraction of the total device resistance in circuit. Carbon-pile rheostats are used as [[load bank]]s for testing automobile batteries and power supplies.

<gallery>
File:Wheatstone Rheostat 1.png|[[Charles Wheatstone]]'s 1843 rheostat with a metal and a wooden cylinder
File:Wheatstone Rheostat 2.png|Charles Wheatstone's 1843 rheostat with a moving whisker
File:RheostatSymbol.png|Electronic symbol for rheostat
File:PreSetRheostatSymbol.png|Electronic symbol for trimmer rheostat
File:pot1.jpg|A high-power wirewound potentiometer
</gallery>