Question

Thermistors have __________
(A) Positive temperature coefficient
(B) Negative temperature coefficient
(C) Zero temperature coefficient
(D) Infinite temperature coefficient

Answer 1

Hint: We know that the resistance-change factor per degree Celsius of temperature change is called the temperature coefficient of resistance. This factor is represented by the Greek lower-case letter alpha ($\alpha$). A positive coefficient for a material means that its resistance increases with an increase in temperature. A positive temperature coefficient (PTC) refers to materials that experience an increase in electrical resistance when their temperature is raised. Materials which have useful engineering applications usually show a relatively rapid increase with temperature, which signifies a higher coefficient.

Complete step-by step answer:
We know that thermistor is a resistance thermometer, or a resistor whose resistance is dependent on temperature. The term is a combination of “thermal” and “resistor”. It is made of metallic oxides, pressed into a bead, disk, or cylindrical shape and then encapsulated with an impermeable material such as epoxy or glass.
It should be known to us that thermistors are used as temperature sensors. They can be found in everyday appliances such as fire alarms, ovens and refrigerators. They are also used in digital thermometers and in many automotive applications to measure temperature.
Thermistor generally has a negative temperature coefficient of resistance. With increase in temperature, resistance of a thermistor decreases.

Hence, the correct answer is Option B.

Note: We should know that the effect of heat on the atomic structure of a material is to make the atoms vibrate, and the higher the temperature the more violently the atoms vibrate. In a material where the resistance increases with an increase in temperature, the material is said to have a POSITIVE temperature coefficient. The resistance increases as the temperature of a metallic conductor increases, so the resistance is directly proportional to the temperature. Since the flow of electrons through any medium will develop heat, all resistors will be subject to changes in temperature. This means that composition resistors will decrease in resistance with an increase in temperature, while metallic types will increase in resistance with an increase in the temperature.