Atomic Spectra

[reginacabanban1I]

How do you know the principle quantum number "n" from a given wavelength?

[Annie Qing 2F]

First, solve for the wavelength's frequency by the equation where c is the speed of light. The energy of that frequency can be solved for by the equation where h is Planck's constant. You can then find the principle quantum number (n) that correlates by the equation where R is Rydberg's constant.
Note that the wavelength given would have to correspond to that of a specific energy level. Usually, this isn't the goal of problems. You'd probably more likely be asked about the change between principle quantum numbers (n) and the energy in the form of light emitted, in which you'd be given the wavelength of light emitted by the change in energy levels or other relevant information.

Please correct me if I'm wrong on any of this!