If we combine the expressions relating energy change and frequency of the transition radiation, we get
The corresponding equation for the wavelength is
where R (= 1.0973
If nf = 2, the above expression gives the wavelengths corresponding to the Balmer series. The first four of these transitions (ni = 3, 4, 5, and 6) produce lines with wavelength 656, 486, 434, and 410 nm. These photons are in the visible range and were the first to be observed from excited hydrogen atoms. These lines were among the first pieces of evidence of that pointed toward quantized behavior. The other series produce lines outside the visible range but have been observed using special detection systems.
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