Electron orbits, Sommerfeld model, Atomic Spectra of hydrogen atom
1. Perspective of Modern Physics by Beiser, McGraw-Hill, (1988)
Page no. 118-122, Page no. 124-136
2. Atomic and Quantum Physics by H. Haken and H. C. Wolf, Springer, (1994)
Page no.106
http://www.met.reading.ac.uk/pplato2/h-flap/phys8_2.html