What is the number of photons of light with a wavelength of 4000 pm that provide 1J of energy?


Given:

Wavelength, λ = 4000 pm


Energy, E = 1 J


By Planck’s relation we have,


Energy, E = h×v


But we know v = [c] / [λ]


Where


c = Speed of Light


v= Frequency


λ = Wavelength


So, E = hc /λ


= [[6.626×10-34] × [3×108]] / [4000×10-12]


= [1.9878×10-25] / [4000×10-12]


= 4.9695×10-17 J


4.9695×10-17 J is the Energy of 1 photon


So, 1 J is the energy of X number of photons


X = [1] / [4.9695×10-17]


X = 2.012×1016 photons


So, the number of photons which provide 1 J of energy is 2.012×1016 photons.


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