Apologies, but I have another photoelectron question. In this one I get a result that seems reasonable, however it does not show up on my list of work functions that I have available to choose from. The problem is: A photoelectric-effect experiment finds a stopping potential of 1.93V when light of 200nm is used to illuminate the cathode. What is the cathode made of? I initially thought this would be an easy problem as Vstop = (hf - Eo) / e I have all the values except Eo which is what I am trying to solve for. Vstop = 1.93 V h = 4.14x10^-15 eV f = 3x10^8/200x10^-9 = 1.5x10^15 e = 1.6x10^-19 So, I plug all of the values into the equation and solve for Eo 1.93 = ((4.14x10^-15)(1.5x10^15)-Eo)/1.6x10^-19 The resulting value of Eo was 6.21 This seems valid, except the list I have to choose from is: Potassium: 2.3 Sodium: 2.75 Aluminum: 4.28 Tungsten: 4.55 Copper: 4.65 Iron: 4.7 Gold: 5.1 Likely I am having the same problem as my previous question and not seeing a simple unit difference. Anyhow, I do appreciate your help.