Class 12 Physics Wave Optics Huygens Theory

Huygens Theory

• According to Huygens light can be of wave nature.

• He got this idea from the simple observation:
• In an experiment conducted by Newton and Huygens, two rooms were considered with an obstruction in the middle. Newton considered a boundary and Huygens considered a door as the obstacle between rooms. In this experiment, light was switched on in one room.
• According to Newton if light travels in straight lines then first room will be bright and some portions of the second room will become bright and the rest of the room will be dark.
• Huygens observed that the first room became bright and the light spread in the second room as well, but it was not as bright as the first room.
• Therefore Huygens’s proposed that light might be of a wave nature.
• As the wavelength of light is so small thereforethe wave nature of light cannot be seen.
• If the light is made to pass through a small portion which is comparable to the wavelength of light,then the wave nature of the light can be observed.
• According to Huygens, Newton’s theory was not fully correct.Therefore he gave an idea that the light is of wave nature.
• For example:-
• If a light is made to pass through a big window then the light will appear as ray and not the wave.
• But if the light is made to pass through a very small hole then the wave nature can be observed.
• Huygens’s idea was not accepted because of the following reasons:-
• As there was no experimental proof of what Huygens proposed.
• There was Newton’s authority at that time.
• Wave always needs a medium for propagation. This means light cannot propagate in vacuum.But sunlight is able to reach earth surface.
• Conclusion given by Huygens formed the basis of wave nature of light.
• Many other scientists came after Huygens to prove light is of wave nature :-
• Thomas Young (1800)– Young performed very important experiment known as Young’s double-slit experiment. He was able to prove:
• The wave nature of light.
• Maxwell(1860)- Maxwellgave the Maxwell’s EM theory of light.
• He was able to provethere are visible light in the Electromagnetic spectrum.
• He supported the wave nature of light and he also predicted the speed of the light.
• After Maxwell, the wave nature of light was accepted and Newton’s corpuscular theory was proved wrong.
• Around 1900 some of the scientists observed the photoelectric effect.
• In photoelectric effect when the light falls on the metal surface, electrons get ejected from the metal surface.
• Einstein explained the photoelectric effect by the particle nature of light.

Light: A particle or a wave: Conclusion

• Dual nature of light.
1. Light has both wave as well as particle nature.
2. Light can behave either as a particle and or a wave depending on the situations.
3. Dual nature is also shown by electrons.
• When particle nature of light is considered then the Photoelectric effect, ComptonEffect, etc. can be considered.
• When wave nature of light is considered then wave properties such as interference, diffraction, polarization, etc. are considered.

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