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Q & A: Temperature dependence of a carbon resistor

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Most recent answer: 01/06/2012
Q:
What is a Carbon Resistor? How does its resistivity vary with increase in temperature (graph)? will it decrease as in the case of semi-conductors or will it increase as in the case of metal/wire-wound resistors?
- Afzovich (age 17)
Doha, Qatar
A:
Hello Afzovich, welcome to our website,
Carbon resistors have several different forms.   One is a mixture of ceramic powder and fine carbon granules held together with a resin type of glue.  This has pretty much been discontinued since the advent of modern printed circuit boards where space is at a premium.  The type most used these days is a small ceramic base on which a resistive pattern has been deposited.   In both cases, the ceramic base is non conducting whereas the carbon forms a current carrying path;  the more carbon, the less the resistance.
  This type of carbon has a negative thermal coefficient, i.e. the higher the temperature, the lower the resistivity.  Its value depends on the details of the form of carbon but often is about -0.0005/C near room temperature .   So if you heat a 1000 Ω resistor by 10 C then it will have a resistance of 1000 Ω *(1-0.0005*10) = 995 Ω.

LeeH

(published on 01/06/2012)

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