A thermistor used as a temperature sensor is NTC. If the temperature rises, what happens to the resistance and current for a fixed supply voltage?

• A. Resistance decreases; current increases (I = V/R).
• B. Resistance increases; current decreases
• C. Resistance stays the same; current stays the same
• D. Resistance decreases; current decreases

Answer: (B)

An NTC thermistor decreases its resistance as temperature rises. With a fixed supply voltage, current follows Ohm’s law: I = V/R. So when the resistance falls, the current must rise. Therefore, as temperature increases, the thermistor’s resistance decreases and the current increases. This contrasts with a device that has a positive temperature coefficient, which would show resistance increasing and current decreasing with higher temperature.