Question

why does the bohr model fail to account for finer details of hydrogen atom spectrum(doublet),what exactly is the theory behind doublets and triplets

Answer 1

Bohr's model is for one electron system and is applicable to hydrogen like atom. The doublet or triplet are produced when each spectral line is subjected to high resolution. This is done in the presence of electric or magnetic filed. This resolution is possible if there is multiple non circular orbits corresponding to each energy levels. But according to Bohr electrons revolves in circular orbits only. That is why doublet or triplets are not explained.