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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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Photo electric effect | Quantum mechanics | Physical basis of quantum mechanics

Photo electric effect

Photo electric effect

  • When light or E.M. radiation of suitable frequency or wavelength falls on a metal surface, it emits electrons.
  • The process of emission of electrons from a metal surface, when illuminated by light of suitable wavelength or frequency is photoelectric effect.
  • The electrons so emitted are photoelectrons.

Experimental Arrangement 

  • T = An evacuated glass tube with a quartz window W
  • P = Photoelectrical sensitive plate
  • C = Hollow cylinder which have a small hole to permit the incident light
  • G = A sensitive galvanometer or ammeter
  • P is connected with negative end of a battery with G
  • C is connected with positive end of a battery

Working

  • When light of suitable frequency falls on P from a source, the photoelectrons are emitted.
  • Since collecting cathode C is connected to positive terminal of battery, so these electrons are attracted towards C.
  • Thus photo electric current (IC) flows from P to C, and this current can be detected or measured by G.
  • IC increases as the potential of C is more and more positive with respect to P.

Laws of photoelectric emission

  • For every metal there is a particular frequency below which there is no photoelectric emission.
  • The minimum frequency required for photoelectric emission is threshold frequency.
  • As the intensity of incident light (IP) increases, IC also increases, i.e. IC ∝ IP.
  • When the frequency of incident light is greater than threshold frequency.

  • On increasing the positive potential of C, IC increases and it become maximum at a particular value of potential.
  • A particular positive potential of collecting cathode C at which the photoelectric current is maximum, is known as saturated current.
  • On increasing the negative potential of C, IC decreases and it become zero at a particular value of potential.
  • The energy of the emitted photoelectrons is independent of intensity of incident light, and depends on the frequency of incident light and nature of the metal.
  • Photoelectric emission is an instantaneous process.


Failure of the electromagnetic theory

  • The calculation shows that the electron take 500 days to eject from sodium by using visible light of wavelength 4000Å, whereas experimentally there is no time delay.
  • According to classical theory, light of greater intensity should impart large kinetic energy to the ejected electrons. But this does not happen.
  • Classical theory shows that the velocity (energy) of the ejected electron should not depend on the frequency of the incident light, but in actual it depends.
To know more about this lecture please visit on https://youtu.be/FeTNKz3RqBc

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