Question

A sodium flame has a characteristic yellow color due to emissions of wavelength 185 nm. What is the mass equivalence of one photon of this wavelength (1 J = 1 kg·m2/s2)?

Answer 1

This can be solved by DE BROGLIES equation

Wavelength= Planks constant divided by momentum=h/p

therefore momentum=planks constant/wvelength

wavelength of 1 photon=185nanometer=185*10^(-9)meters

planks constant h=6.63*10^(-34)JS

So momentum of photon= Planks constant/ wavelength= 6.63*10^(-34)/185*10^(-9) = 6.63/185 x 10^(-25)

=0.0358 x10^(-25) kgm/s=3.58 x 10^(-27) kgm/s

then mass of photon =momentum/velocity of photon

velocity of photon= 3x10^8 m/s which is a constant

therefore mass of photon= 3.58 x10^(-27)/3 x10^(8) = 1.193 x10^(-35) kg

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