CBSE Class 11-science Answered

Wave number is defined as the number of wavelengths per centimetre and is equal to the inverse of wavelength expressed in centimetre. It is dented by and is expressed in cm^-1.  A wavenumber can be converted into quantum-mechanical energy E in J or regular frequency ? in Hz according to

,

.

Note that here wavenumber and the speed of light are in cgs units, so care must be taken when doing these calculations.

For example, the wavenumbers of the emissions lines of hydrogen atoms are given by

where R is the Rydberg constant and n_i and n_f are the principal quantum numbers of the initial and final levels, respectively (n_i is greater than n_f for emission).