1. The problem statement, all variables and given/known data A laser of frequency f0 is connected to a spring which oscillates in one dimension with a period T and amplitude A. The laser excites the 1st four Paschen series lines of hydrogen. What is f0 2. Relevant equations I'm assuming that I'll need the Doppler shift equations, f = f0[ (1 + β) / (1 - β) ]1/2 (for approaching) and f = f0[ (1 - β) / (1 + β) ]1/2 (for receding) Where β = v/c 3. The attempt at a solution I've identified the Paschen series for hydrogen to be 1870 nm, 1280 nm, 1090 nm, and 1000 nm. I don't understand where I should go next. Initially I thought that I could plug values into the equation and solve for the original frequency but I don't see what values I could put in. For an oscillating spring, there will be infinity values of the velocity from 0 to whatever the maximum velocity is. So I don't see how I could solve it? Part 2 of the problem also asks what the maximum velocity of this oscillation must be to give the observed lines. Any suggestions are much appreciated.