(a) Starting from the expression for the discrete energy levels of a hydrogen atom, derive a formula for the wave number λ1 of the photon emitted when an electron makes a transition from an initial orbit n2 to a lower orbit n1 (n2>n1).
(b) Using your result, calculate the wavelength of the photon emitted when the electron in a hydrogen atom drops from the fourth to the second orbit.
(c) Name the spectral series to which this transition belongs.
Use h=6.63×10−34Js, c=3.00×108ms−1, and 1eV=1.60×10−19J.