Atomic Spectra

Moseley studied the -ray spectra of various elements. The spectral line observed were of
(i) short wavelength series and 
(ii) long wavelength series. line is most intense in the -series. Moreover, he observed that the wavelength of the line decreases with increase in the atomic number of the element as the target. If a graph is plotted between the square root of the frequency and the atomic number of the element emitting the line, it is a straight line Thus,  
Where is the frequency of the radiation and is the atomic number of the element.