A metal has a work function of 2.0 e V and is illuminated by monochromatic light of wavelength 500 n m . Calculate ( h = 6 .6 × 10 - 34 Js , c = 3 × 10 8 m / s ) The threshold wavelength The maximum energy of photoelectrons The stopping potential

(i) Given, Work function, W 0 = 2.0 e V = 2 .0 × 1 .6 × 10 - 19 J Wavelength of monochromatic light is , λ = 500 n m Say, the threshold wavelength is λ 0 . Expression for work function, W 0 = h c λ 0 ∴ λ 0 = h c W 0 = 6.6 × 10 - 34 × 3 × 10 8 2.0 × 1.6 × 10 - 19 m ∴ λ 0 = 6.1875 × 10 - 7 m = 6187.5 Å (ii) According to Einstein’s photoelectron equation, the maximum kinetic energy is given by, K m a x = h c λ - W 0 K m a x = 6.6 × 10 - 34 × 3 × 10 8 500 × 10 - 9 × 1.6 × 10 - 19 - 2.0 e V K m a x = 2.475 - 2.0 = 0.475 e V (iii) Stopping potential, V 0 = K m a x e = 0.475 V