The maximum kinetic energy of photoelectrons is 3.30 eV. When the wavelength of the light is increased by 50%, the maximum energy decreases to 1.50 eV. What is the work function of the cathode? What is the initial wavelength? K= E_elec - deltaE K_max = hf - E_0 = E_elec - E_0 f = c/(lambda) so I set K=K_max and get: E_elec - deltaE = E_elec - E_0 and solved for E_0 with deltaE= 1.5 eV - 3.3 eV, but then I get a negative work function (E_0)= -1.8, can work functions be negative? I also get the feeling that I'm not using the kinetic energy equations correctly here. For the initial wavelengthI took (3/2)(lambda_i) = hc/E for E I used 1.5 eV and I got it wrong as well, and that was the last of my tries and the told me the answer was 230 nm, but I still can't see how they came to that because the book barely goes over these topics, and we didn't spend that much time on it during lecture. Is there an equation that I'm supposed to use that I'm missing?