Wavelength of a laser exciting H atom from n =2 to n = 5

[Linus Pauling]

1. A monochromatic laser is exciting hydrogen atoms from the n = 2 state to the n = 5 state. What is the wavelength of the laser?



2. frequency = f = delta E / h
lambda = c/f



3. First, is the following approach valid:

I find delta E by computing E₅ - E₂, where E_n = n²h²/8mL²

I then divide that answer by h to obtain f, then do c/f = lambda.

If that's a valid approach, then I am confused as to what I use for L in the E_n formula.

 

[Linus Pauling]

Nevermind, I got it.