What is a thermistor and how does its resistance change with temperature?

• A. A thermistor is a resistor whose resistance changes with temperature; an NTC thermistor decreases in resistance as temperature rises, while a PTC thermistor increases with temperature.
• B. A thermistor is a resistor that always increases resistance with temperature.
• C. A thermistor is a device that stores energy without changing resistance.
• D. A thermistor has fixed resistance regardless of temperature.

Answer: (C)

A thermistor is a temperature-sensitive resistor whose resistance changes with temperature because the semiconductor material inside responds to heat. In the common type, resistance decreases as temperature rises (NTC), since higher temperature increases charge carriers and makes conduction easier. Some thermistors (PTC) do the opposite, increasing resistance with temperature. This varying resistance lets the thermistor be used to sense temperature or provide temperature-dependent behavior in circuits. The idea that it stores energy without changing resistance or that its resistance is fixed regardless of temperature isn’t correct, and those descriptions don’t fit how a thermistor behaves.