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 En = 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 En formula.