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PHOTOELECTRIC EFFECT

PHOTOELECTRIC EFFECT. BY: ARUSHI TRIPATHI. WHAT DOES PHOTOELECTRIC EFFECT MEANS??. The phenomenon of emission of electrons from metal under the effect of light is called photoelectric effect.

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PHOTOELECTRIC EFFECT

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  1. PHOTOELECTRICEFFECT BY: ARUSHI TRIPATHI

  2. WHAT DOES PHOTOELECTRIC EFFECT MEANS?? • The phenomenon of emission of electrons from metal under the effect of light is called photoelectric effect. • The electrons emitted by photoelectric effect are called photoelectrons and the current produced is called photoelectric effect. • In this effect the light of short wavelength is more effective.

  3. HISTORY • First observed by Hertz in 1887 • After one year , Hallwachs confirmed by an experiment by using zinc plates. • In 1898 J.J. Thompson established • When light falls on a metal surface , electrons are emitted from the surface. • Finally understood by Lenard in 1900 • Various experiments were conducted by Lenard and Millikan.

  4. THE PHENOMENON

  5. DEPENDENCE ON VARIOUS FACTORS • Dependence on intensity of light : • Light ray of definite intensity fall on plate P , photons are emitted. • plate C is positively charged, all these photons reach plate C. • Increase in positive potential does not results in increase in number of photons. • Increase in intensity of light results in increase of photons. • Hence increase in the current.

  6. Dependence On Frequency: • If at stopping potential , light of frequency higher than before be made to fall on P , current is established. • Higher the frequency higher will be the maximum kinetic energy. • Lowest frequency which can emit photons from a material is called threshold frequency or cut-off frequency of that material.

  7. EINSTEIN’S EXPLANATION • In 1905 Einstein explained photoelectric theory . • The intensity of light depends on the number of these photons. • When photons fall on a metal, it transfers “whole” of its energy to any “one” of the electron present in the metal and its own existence is vanished.

  8. Energy Of a Photon • Rest mass = zero, but kinetic mass not • zero. • Photon travels with the speed of light. • Einstein's mass energy relation (E=mc ˆ2) • Energy of photon E= hv/c^2

  9. ADVANTAGES: • Used in turning on motor. • Used for switching on & off street . • Used in cameras . • Used in industries. • Used in solar cells for conversion of light energy into electric energy.

  10. THANKYOU

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