A monochromatic source emitting light of wavelength 600 nm has a power output of 66 W. Calculate the number of photons emitted by this source in 2 minutes.

Explanation

Energy of one photon
`E=(hc)/(lambda)`
`E=(6.6 xx 10^(-34) xx 3 xx 10^(8))/(6 xx 10^(-7))`
`=3.3 xx 10^(-19)` J
`E_(1)="energy emitted by the source in one second"`
= 66 J
`:.` Number of photons emitted by the source in 1 sec.,
`n=(66)/(3.3 xx 10^(-19))`
`= 2 xx 10^(20)`
`:.` Total number of photons emitted by source in 2 minutes,
`N=n xx 2 xx 60`
`= 2 xx 10^(20) xx 120`
`= 2.4 xx 10^(22)` photons