Drawing the spectral lines every time in order to calculate number of spectral lines can be time consuming. Suppose you have to calculate the number of spectral lines when an electron comes from the excited state N = 5 to its original state. When you follow the traditional method, you have to draw out all the possible transitions.
But a small trick can help us to calculate spectral lines in no time. In this, you should know the transition state and you are all set.
Want to practice? Try these
All the electrons in a sample of the hydrogen atom are excited to n = 7 level. The number of emission spectral lines possible are: