An experimental vacuum tube uses a cesium-coated cathode illuminated by a calibrated ultraviolet source. Monochromatic UV photons, each carrying an energy of 6.2×10−19 J6.2 \times 10^{-19} \text{ J}6.2×10−19 J, strike the cathode surface, causing the emission of photoelectrons. The maximum velocity of the ejected photoelectrons is measured to be 6.4×105 m s−16.4 \times 10^5 \text{ m s}^{-1}6.4×105 m s−1.
What is the work function of this cesium-coated surface?
(Take the mass of an electron, me=9.11×10−31 kgm_e = 9.11 \times 10^{-31} \text{ kg}me=9.11×10−31 kg)
1.9×10−19 J1.9 \times 10^{-19} \text{ J}1.9×10−19 J
2.5×10−19 J2.5 \times 10^{-19} \text{ J}2.5×10−19 J
4.3×10−19 J4.3 \times 10^{-19} \text{ J}4.3×10−19 J
8.1×10−19 J8.1 \times 10^{-19} \text{ J}8.1×10−19 J
