15. The work function of sodium is 2.0 eV. A beam with a wavelength of 500 nm (= 500 × 10⁻⁹ m) illuminates the surface, what is the maximum kinetic energy of the photoelectrons? Here 1 eV = 1.6 × 10⁻¹⁹ J, the Plank's constant h = 6.6 × 10⁻³⁴ J·s, and the speed of light c = 3.0 × 10⁸ m/s. (A) 1.0 eV (B) 4.5 eV (C) 0.5 eV (D) 2.5 eV (E) 2.0 eV