a) Sunlight with visible wavelengths ranging from 200 to 500 nm is incident on a sodium surface. The work function of sodium is 2.28 eV. Determine the maximum kinetic energy (in joules) of photoelectrons emitted from the surface, and the wavelength range that will cause photoelectrons to be emitted? Explain why the kinetic energy of the emitted electrons has a maximum value? b) A proton and an electron have the same velocity. The de Broglie wavelength of the electron is 3.2 x 10-8 m. Calculate the de Broglie wavelength of the proton?