Question

The instrument used to measure the temperature of the source from its thermal radiation is:
A) Hydrometer
B) Barometer
C) Thermopile
D) Pyrometer

Answer 1

Hint: Temperature can be measured by different types of instrument based on the quantity they are measuring. Here we have asked about the instrument which measures temperature from its thermal radiation. So first we will discuss temperature and then the instrument which can be used to measure it.

Complete step-by-step answer:
Basically, temperature is measurement of degree of hotness or coldness of an object, it tells us how hot or cold an object is. It can be measured by different methods based on the quantity it is measuring. Like we use mercury thermometer to measure the temperature of our body, actually in mercury thermometer, there is mercury which senses heat and it expands accordingly giving us temperature.
Similarly, there is a thermometer which can detect the temperature without coming in physical contact by measuring the heat radiating from the body or by measuring thermal radiation. Such a type of thermometer is known as an infrared thermometer or pyrometer.

So, the correct answer is “Option D”.

Additional Information: Thermal radiation is the electromagnetic radiation from a body due to its temperature. The electromagnetic radiation emitted from a body is in the range of the infrared region of the electromagnetic spectrum, therefore the thermometer measuring the thermal radiation is called infrared thermometer.

Note: Pyrometer can measure higher temperature than a normal thermometer like mercury thermometer or digital thermometer.
Thermopile is a device which converts thermal radiation or thermal energy into electrical energy. It can be used as a sensor by not an instrument.