1. The problem statement, all variables and given/known data Find the de Broglie wavelength of a 7.0 eV electron. 2. Relevant equations de Broglie wavelength = h/p = h/(mv) Photoelectric effect equation (not 100% sure) 3. The attempt at a solution i need to solve for v in de Broglie's equation so i can find the wavelength. i know the mass of the electron is 9.11x10^-31kg, i know that h is Plancks constant, and i know that the work function = 7.0 x (1.602x10^-19 J) BUT how can i find v? I tried to find v by using the photoelectric effect equation but i didnt get a correct answer: hf = KE + Work function....BUT how can i solve for v if i dont have the frequency!?