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“Adrishya Alok”: The Scintillating Legacy Of Electromagnetic Waves

It was in 1672 that Isaac Newton experimentally segregated a beam of light into its seven component colours and established the fact that what we consider light is actually a combination of multiple waves having different frequencies and wavelengths. Therefore, it came to light that our perception of colours can be attributed to the reflection of a light wave by an object corresponding to its perceived colour while absorbing all the other components.

However, it was much later, in the nineteenth century, that mankind began to understand that there is more than what meets the eye, literally.

In 1800, astronomer William Herschel, while conducting an experiment to note the temperatures corresponding to different colours of light refracted by a prism, abruptly placed a thermometer on the farther side of the visible red light and, surprisingly, observed that the temperature recorded by this thermometer was the highest. The invisible light rays heating up that thermometer eventually came to be known as infrared rays.

Similarly, the next year, Johann Wilhelm Ritter established the existence of ultraviolet rays by observing that invisible rays beyond the violet end of the spectrum reacted rapidly with a silver chloride solution (a precursor to photography).

In the 1860s, a scientist called James Clerk Maxwell revolutionised the world by upgrading the perception of these visible and invisible light waves to carriers of electromagnetic radiation associated with time-varying and codependent electric and magnetic fields.

Twenty-five years later, Maxwell's theory was verified by Heinrich Hertz using an instrument called the "spark-gap generator" to create and discharge electromagnetic waves having a shorter frequency than visible light (radio waves) and using an open-loop circular detector placed nearby to detect them through the spark they created.

In 1895, Indian scientist Jagdish Chandra Bose discovered waves having frequency as high as 60 GHz (millimetre waves) and demonstrated their presence by igniting gunpowder and using what he termed as "Adrishya Alok" in his Bengali essay, to ring a bell beyond the wall. While Bose got the formal recognition for his contribution around 120 years too late (by the Institute of Electrical and Electronics Engineers), it is this discovery of millimetre waves that forms the backbone of 5G technology as the world swoons over high-speed internet today.


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