A 100W 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. (a) What is the energy per photon associated with the sodium light? (b) At what rate are the photons delivered to the sphere?

Explanation

`P=100W" " lambda=589 nm = 589xx10^(-9)m`
a. `E=h upsilon=h (c )/(lambda)=(6.6xx10^(-34)xx3xx10^(8))/(589xx10^(-9))=0.03xx10^(-17)=3xx10^(-19)J`
b. Let .n. be the number of photons produced/s
then, `nhupsilon=P " "therefore n=(P)/(lambda upsilon)=(100)/(3xx10^(-14))=3.3xx10^(20)`