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MODERN PHYSICS IS A VERY EASY AND SCORING PORTION IN THE JEE SYLLABUS SO HERE R SOME IMP PTS , DEFINATELY CONCEPT BUILDERS !!!!!!

*When radiation interacts with matter it behaves as if made of packets of energy/quanta . If their wavelength range lies in the visible region they r named photons

*Einstein?s energy relation E=( c^2p^2+mo^2c^4 )^1/2. For photon rest mass mo=0 (as we can?t define a reference frame in which a photon is at rest rather it always moves with speed c) so E=pc

P.S :This relation is not valid for electrons, protons, neutrons for which rest mass is non zero

*All photons of a particular wavelength of light have same energy and momentum

*Moving mass of photon is defined as m=E/c^2 or hf/c^2 or h/cl l=wavelength

*Photons r electrically neutral and r not deflected in electrc and magnetic fields

*If intensity of given wavelength of light is increased there is no increase in energy of photon but no of photons emitted per unit time unit area increase

*Photons exert pressure

For PERFECTLY ABSORBING SURFACES pfinal (momentum)=0

Force exerted =rate of change of momentum

P=F/A=dp/Adt=E/Adtc= I/c I=intensity=energy per unit area per time

For PERFECTLY REFLECTING SURFACES

P=F/A=dp/Adt=2E/Adtc=2I/c pfinal= -pinitial

*For photon wavelength is directly proportional to V (accelerating potential)

whereas for electrons it is inversely proportional to square root of V

*On collision with other particles momentum and energy is conserved but not the no of photons

*Photon theory supports quantum theory becoz i)there is a definite frequency known as threshold frequency beyond which photoens r emited ii)even on faint illumination photoelectrons r emitted

Self Written

HOPE U'VE BEEN BENEFITED !!!!!!!!!!

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