A 100 W sodium lamp radiates energy uniformly in all directions. The lamp is located at the centre of a large sphere that absorbs all the sodium light which is incident on it. The wavelength of the sodium light is 589 nm.
What is the energy per photon associated with the sodium light ?

Explanation

Given, `P = 100 W, lambda = 589 nm = 589xx10^(-9)m, h = 6.63xx10^(-34)J-s, c = 3xx10^(8)m//s`
`E =(hc)/(lambda)=(6.63xx10^(-34)xx3xx10^(8))/(589xx10^(-9))=3.38xx10^(-19)J = (3.38xx10^(-19))/(1.6xx10^(-19))eV = 2.11 eV`.