1. The problem statement, all variables and given/known data Hi! I'm writing my lab report on the Franck-Hertz experiment and I have trouble with the contact potential difference (inelastic collision). How do you calculate it? 2. Relevant equations See below 3. The attempt at a solution The energy differences between the maximum and minimum peaks lies around 4.9 eV (4.9 +/- 0.5 eV approx.) , which is the "correct" value. When it comes to the contact potential difference, I guess that I can calculate it by calculating the average between two peaks and then subtract it from the first peak? But I'm not sure.