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Can anyone help me find some causes as to why a resistor may become non-ohmic?

Thanks in advance.

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  • \$\begingroup\$ If you make a resistor using thin wire, say steel, you will find that the resistance increases with wire temperature. So that is one example. There are special resistors designed to have a temperature dependence. Some have a negative temperature coefficient (NTC) and some have positive (PTC). They can be used for temperature sensing or other special uses (for example PTC's can act somewhat like a fuse, and NTC's can act as inrush limiters). \$\endgroup\$ – mkeith May 20 '18 at 6:30
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    \$\begingroup\$ You need to define what you mean by non-ohmic. Has the component become open circuit and in effect looking like nearly infinite resistance? Has the component become a short circuit? Or is it still acting somewhat like a resistor but not in a linear relationship between current through and voltage drop across? \$\endgroup\$ – Michael Karas May 20 '18 at 6:35
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    \$\begingroup\$ now that i think about it, this looks like a school question .... is it a school work? \$\endgroup\$ – jsotola May 20 '18 at 6:39
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An ideal resistor follows Ohm's law by definition.
Materials which do not follow Ohm's law are not called resistors. That being said, it is possible that a material that follows the law under standard conditions fails to do so under a wide range of conditions.
Two reasons that come to mind are,

  • The Skin Effect: Which is applicable to High frequency AC circuits
  • Thermal Dependence of resistivity, because of which the nature of the conductor changes with temprature.
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    \$\begingroup\$ Be careful that you are not doing homework for the OP (original poster). If we suspect that it is a homework we usually prompt the OP with some clues to let him/her think it through themselves. They're supposed to be studying the subject so they should already have enough background information. \$\endgroup\$ – Transistor May 20 '18 at 9:17

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