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  • Himani Vora

LIGHT-A WAVE OR A PARTICLE ?



Traveling billions of miles across the universe, reflecting into the cornea of our eyes, sending a stimulus to the Occipital lobe of our cerebrum is the extent of the journey which light travels so we can enjoy the starry night sky. Light-a form of energy providing us with the power of vision and factor contributing to photosynthesis .


But what is this mystical energy … a wave or a particle? First the basics, a wave is an oscillation which leads to the transfer of energy from one place to another and interfere with each other. Particles are completely different, they are single, minute and finite objects which have momentum (product of mass and velocity ) and positions. Interestingly, light is kinda made up of both!


Observation 1 :When two beams of lights cross paths they don’t interact with each other. If light were made of particles they would bounce off each other scattering in all directions but instead the beams overlap each other causing an ‘interference pattern’.

These patterns can only be made by waves when they occupy the same space which in turn led to the conclusion that light is made up of waves.


So it’s settled? Light is a wave. Not so fast!


Observation 2:In the nineteenth century an experiment was conducted where ultraviolet light rays were shined on a metal surface and the energy transferred to the atoms of the metal. We detect electrons (negatively charged subatomic particles ) being emitted from the metal surface.


Both of these contradicting observations created a dilemma about the nature of light.Naturally Einstein was first to explain this bizarre phenomenon. Einstein theorized that electromagnetic energy-light ,comes in discrete packets called quanta. Thus,, light behaves like a particle and a wave depending on how it is observed. Thus resulting in the formation of the concept of wave-particle duality for which Einstein won a Nobel Prize in 1921.




Miraculously this baffling idea led to a new revolutionary theory called Quantum Mechanics-a field in mechanics which tries to explain how the universe works at a subatomic scale .An attempt to unfold the laws of the physical universe has completely transformed how we view the universe .


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Arin Nitin Chandurkar
Arin Nitin Chandurkar
Nov 12, 2021

Well written. But here I have a point here to say. In the experiment in the 19th Century about the actinic rays, in the first para you mentioned that light is - "reflecting into the cornea of our eyes, sending a stimulus to the Occipital lobe of our cerebrum is the extent of the journey which light travels so we can enjoy the starry night sky" and by this it is quite evident that you are talking about the visible light i.e. the wavelength between 400-800 nm. Ultraviolet belong to the EM spectrum beyond the violet part of it. So it may be an EM wave but cannot be classified as "Light" as mentioned by you in the first para.…

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