7. A metal surface is illuminated with light having a wavelength of 400 nm. The work function for sodium metal is 2.5 eV. (A) Find the maximum kinetic energy of the ejected photoelectrons. (hc = 1240 eV nm) (B) Find the cutoff wavelength for the metal. (15p) 8. Calculate the de Broglie wavelength for an electron (me 9 x 10-31 kg) moving at 3 x 107 m/s and a dog (m 10 kg) moving at 3 m/s (h = 6 x 10-34) (15p)