Reverse the voltage Photo Electric Effect Photon Energy = Work + Kinetic Energy hf =  + Emax hf = hfo + eV  - Work function (Depends on material) fo - Lowest frequency that ejects e - Electron charge V - The uh stopping potential + - V Reverse the voltage

Example 1: A certain metal has a work function of 3. 25 eV Example 1: A certain metal has a work function of 3.25 eV. When light of an unknown wavelength strikes it, the electrons have a stopping potential of 7.35 V. What is the wavelength of the light? (1.17059E-07 m = 117 nm)

Example 2: 70. 9 nm light strikes a metal with a work function of 5 Example 2: 70.9 nm light strikes a metal with a work function of 5.10 eV. What is the maximum kinetic energy of the ejected photons in eV? What is the stopping potential? (12.4 V would stop the electrons.)

Ag (silver) 4.26 Au (gold) 5.1 Cs (cesium) 2.14 Cu (copper) 4.65 Li (lithium) 2.9 Pb (lead) 4.25 Sn (tin) 4.42 Chromium 4.6 Nickel Metal Work Function

Photons of a certain energy strike a metal with a work function of 2 Photons of a certain energy strike a metal with a work function of 2.15 eV. The ejected electrons have a kinetic energy of 3.85 eV. (A stopping potential of 3.85 V) What is the energy of the incoming photons in eV? Photon energy = Work function + Kinetic energy of electron Photon energy = 2.15 eV + 3.85 eV = 6.00 eV 6.00 eV

Another metal has a work function of 3. 46 eV Another metal has a work function of 3.46 eV. What is the wavelength of light that ejects electrons with a stopping potential of 5.00 V? (2) E = hf = hc/, Photon energy = Work function + Kinetic energy of electron Photon energy = 3.46 eV + 5.00 eV = 8.46 eV E = (8.46 eV)(1.602 x 10-19 J/eV) = 1.3553 x 10-18 J  = hc/E = (6.626 x 10-34 Js)(3.00 x 108 m/s)/(1.3553 x 10-18 J)  = 1.4667x 10-07 m = 147 nm 147 nm

112 nm light strikes a metal with a work function of 4. 41 eV 112 nm light strikes a metal with a work function of 4.41 eV. What is the stopping potential of the ejected electrons? (2) E = hf = hc/, 1 eV = 1.602 x 10-19 J Photon energy = Work function + Kinetic energy of electron E = hf = hc/ = (6.626 x 10-34 Js)(3.00 x 108 m/s)/(112 x 10-9 m) E = 1.7748 x 10-18 J E = (1.7748 x 10-18 J)/(1.602 x 10-19 J/eV) = 11.079 eV 11.079 eV = 4.41 eV + eVs 11.079 eV - 4.41 eV = 6.6688 eV = eVs Vs = 6.67 V 6.67 V

256 nm light strikes a metal and the ejected electrons have a stopping potential of 1.15 V. What is the work function of the metal in eV? (2) E = hf = hc/, 1 eV = 1.602 x 10-19 J Photon energy = Work function + Kinetic energy of electron E = hf = hc/ = (6.626 x 10-34 Js)(3.00 x 108 m/s)/(256 x 10-9 m) E = 7.7648 x 10-19 J E = (7.7648 x 10-19 J)/(1.602 x 10-19 J/eV) = 4.847 eV 4.847 eV = Work function + 1.15 eV 11.079 eV - 1.15 eV = 3.70 eV 3.70 eV