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Photon

According to Eienstein’s quantum theory, light propagates in the bundles (packets or quanta) of energy, each bundle being called a photon and possessing energy.
 
Energy of photon Energy of photon is given by 99894.png where c = speed of light, h = Planck’s constant = 6.6 × 10–34 J-s, v = frequency in Hz, λ = wavelength of light.
 
 
In electron volt, 99903.png
 
Mass of photon Actually rest mass of the photon is zero. But its effective mass is given as
99909.png. This mass is also known as kinetic mass of the photon.
 
Momentum of the photon
 
Momentum, 99915.png
 
Number of emitted photons The number of photons emitted per second from a source of monochromatic radiation of wavelength λ and power P is given as 99921.png, where E = energy of each photon.
 
Intensity of light (I) Energy crossing per unit area normally per second is called intensity or energy flux
 
i.e., 99927.png99933.png
 
 
At a distance r from a point source of power P, intensity is given by 99939.png
 
Number of photons falling per second (n) If P is the power of radiation and E is the energy of a photon then n = P/E.




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