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National Bird Day: Why Birds Matter to Us

National Bird Day is celebrated every year on 5 January . This day is observed to spread awareness about birds, their importance in nature, and the need to protect them. Birds are beautiful living beings and play a very important role in keeping our environment healthy. Origin of National Bird Day National Bird Day was first celebrated in the year 2002 . It was started by bird lovers and environmental groups to protect birds from dangers like deforestation, pollution, and illegal hunting. The main aim of this day is to teach people, especially students, why birds are important and how we can help save them. Why Is National Bird Day Celebrated Every Year? National Bird Day is celebrated every year because many bird species are disappearing due to human activities. Cutting trees, using plastic, pollution, and climate change are harming birds and their homes. This day reminds us that: Birds need protection Nature should be respected Everyone has a responsibil...
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Law of reflection by Fermat’s principle | Optics

Law of reflection by Fermat’s principle

Fermat's principle

  • According to Fermat’s principle of extremum path, a ray of light in passing from one point to another through a set of media by any number of reflections or refractions selects a path for which the time taken is either minimum or maximum.

Law of reflection by Fermat's principle


  • Since whole path is travelled by light in air.
  • So, the optical path between A and B is
  • l = AO + OB
  • l = √{a2 + x2} + √{b2 + (c - x)2)}
  • From Fermat’s principle, the position of point O is such the optical path l should be either maximum or minimum.
  • dl/dx = 0
  • Therefore

  • ∴ sin i = sin r
  • or ∠ i = ∠ r

Conclusion

  • Since  i  is angle of incidence and  r  is angle of reflection
  • So, for reflection form any surface, the angle of incidence should be equal to the angle of reflection.
  • The incident ray, reflected ray and normal to the reflecting surface all should lie in the same plane and that plane is plane of incidence.
To know more about this lecture please visit on https://youtu.be/NUghGA71psg
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