Question

Consider the following statements A and B and identify the correct answer.
A: Thermistors can have only –ve temperature coefficient of resistors.
B: Thermistors with –ve temperature coefficients of resistance are used as resistance thermometers to measure low temperature of the order of $10K$
A. 1) both A and B are true
B. 2) both A and B are false
C. 3) A is true and B is false
D. 4) A is false, but B is true

Answer 1

Resistors that rely upon temperature are collectively called thermistors.That means, the resistance may vary based on the temperature changes. NTC and PTC are two different categories of it.

Complete answer:
As we know, thermistors(thermal resistors) are resistors that rely upon temperature changes. The two categories of it are Positive Temperature Coefficient (PTC) and Negative Temperature Coefficient (NTC). When the temperature increases, PTC thermistor resistance will increase and NTC thermistor resistance will decrease. That is, they show the contrasting behaviour when the temperature varies. Both types of thermistors are used in a variety of application areas.

Thermistors can be employed to generate an analogue output voltage with alterations in corresponding temperature and as such can be considered as a transducer. This is made possible owing to its capability to generate variations in electrical behaviour which can be further attributed to external and physical change in heat. Usually the variation of resistance depending upon the temperature is not preferable; this property is made employed in different applications that utilize detection of temperature.

The main component of a thermistor is, transducer which shows much dependence on temperature. This transducer is made up of metal oxides with semiconducting property. This is then connected with metallised leads that connect it to the attached ceramic disc. This in turn facilitates the thermistor to vary the resistance with respect to the very small deviations in the temperature.

Therefore we can conclude that option B is true.

Note: The temperature dependence of thermistors had made them find applications in the area where precise temperature detection is needed. Refrigerators, electrical ovens, like temperature-dependent appliances, make use of thermistors. When the temperature increases, PTC thermistor resistance will increase, and NTC thermistor resistance will decrease.