Solve the all parts of following problem:
Problem: In a Franck-Hertz type of experiment, atomic hydrogen is bombarded with electrons and excitation potentials are found at 10.21 V and 12.10 V.
Part A: Explain the observation that three different lines of spectral emission accompany these excitations (Hint: Draw an energy-level diagram.)
Part B: Now assume that the energy differences can be expressed as hf and find the three allowed values of f.
Part C: Assume that f is the frequency of the emitted radiation and determine the wavelengths of the observed spectral lines.
Express your knowledge to solve the above problem.