Wize University Physics Textbook (Master) > DC Circuits

Non-Ohmic Resistors

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Non-Ohmic Resistors

Image illustrating Non-Ohmic Resistors



A non-Ohmic resistor doesn't obey Ohm's Law V=IRV=IR. That is, the resistance is not constant.


This means that the graph of the voltage VV vs. the current II is not a straight line.








Examples:

  • Light bulb: as the temperature increases, the ions inside the hot filament move faster, slowing down the passing electrons, and therefore increasing the resistance.
  • Diode: in a diode, the current flows only in one direction, because in the other direction the resistance is very high.
  • LDR (light dependent resistor): as the intensity of the surrounding light increases, the resistance decreases (useful for automatically switchings lights on and off).
  • Thermistor: as the temperature increases, the resistance decreases (useful for turning the heating system on and off).