CHAPTER 12. HOW INFRARED THERMOMETER WORKS.
We all have used a mercury thermometer to measurethe temperature of the body during fever.
Mostly, it is kept in the mouth or in some way orthe other it touches the body of the person. But,
when there is a virus transmitted from person to person,the use of mercury thermometer is very
risky and not feasible.
Also, if you went out during the lockdown you mighthave noticed a gun like a thing that is
placed in front of the person’s head, well, it’s aninfrared thermometer used to measure the
temperature of the body.
Let’s see first what infrared is. Well, infrared iselectromagnetic radiation similar to visible light
that we see, but it is invisible to the human eye.Its frequency ranges from less than 1Hz to over
1025 Hz. It was discovered by William Herschel in 1800when he was trying to find why sunlight,
when passed through different materials, producesdifferent heat. He found during the
experiment that different colours have different temperatures.So he made white light pass
through a prism, which splits white light into 7 coloursof the rainbow. He then measured the
temperature of all 7 colours and noticed that movingtowards red, the temperature increased.
Out of curiosity, he measured the temperature of theregion below red. He was shocked to find
that the temperature in that no colour region wasmuch higher than the colours. This is how
infrared light was discovered. He named it infraredlight, coining two words “ Infra ” a Latin word
for below and “red”.