1. What is the wavelength of a 5.0 eV photon? What is the de Broglie wavelength of a 5.0 eV electron? 2.E = hc/lambda lambda = h/momentum 3. I know the first one simply 248 nm for the wavelngth. I don't know how to find the de Broglie though since I don't know what the momentum of the electron is.