There are two sources of light, each emitting with a power of 100 W. One emits X-rays of wavelength 1nm and the other visible light at 500 nm. Find the ratio of number of photons of X-rays to the photons of visible light of the given wavelength?
Both the sources are of 100W each. Thus, they both give 100 joules of energy in 1 second since
The energy supplied due to any electromagnetic radiation is given by
Where h (Plank’s Constant) = 
c is the speed of light in vacuum = 3 x 108 m/s
is frequency of the electromagnetic radiation
λ is the wavelength of the electromagnetic radiation.
Now, for the source emitting X-rays (wavelength, 1 nm = 
)
For the source emitting visible light (wavelength, 500 nm = 
Power emitted by the source will be equal to
Power is same and equal to 100 W for both the sources.
Where N1 and N2 represent number of photons emitted by sources 1 and 2 respectively.
E1 and E2 represent energy of one photon of the respective sources which has been calculated earlier.
Ratio of number of photons of X-rays (source 1) to number of photons of visible light (source 2)
