Calculate the wavelength, frequency...
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Calculate the wavelength, frequency and wavenumber of a light wave whose period is 2.0 x 10-10 S. What is the number of photons of light with a wavelength of 4000 pm that provide 1J of energy? 2.8

JEE/Engineering Exams
Chemistry
Solution
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Energy (E) of a photon ( =mathrm{hc} / lambda ) Where, ( lambda= ) wavelength of light ( =4000 mathrm{pm}= ) ( 4000 times 10-12 m=4 times 10-9 m ) c = velocity of light in vacuum ( =3 times 108 mathrm{m} / mathrm{s} ) ( mathrm{h}= ) Planck's constant ( =6.626 times 10-34 mathrm{Js} ) thefore the energy of photon (E) ( =6.626 times 10-34 mathrm{Js} times 3 times 108 mathrm{m} / mathrm{s} / 4 times 10-9 mathrm{m}= ) ( 4.965 times 10-16 mathrm{J} ) Now ( 4.965 times 10-16 mathrm{J} ) is the energy of ( =1 ) photon Therefore ( 1 mathrm{J} ) will be the energy of ( =1 / 4.965 mathrm{x} ) ( 10-16 mathrm{J}=2.014 times 1015 ) photons
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