Question

How many light waves are there in a length of 4 micron if the wave length is 5 femto meter?

Answer 1

wavenumber is the spatial frequency of a wave per unit distance. Here we have to find out the number of wave in 4 micrometer(micron).
wavenumber =1/wavelength
Given wavelength=5 femto metre=5*10^-15
therefore wavelenth for 1m=1/5*10^-15
=2*10¹⁴
For 4 micron it is 2*10¹⁴ *4*10^-6
=8*10^8