Question

The work function for caesium atom is 1.9 eV. Calculation (a) the threshold wavelength and (b) the threshold frequency of the radiation. If the caesium element is irradiation with a wavelength 500 nm, calculate the kinetic energy and the velocity of the ejected photo electron.

Answer 1

(a) Work function,

ϕ₀ = 1.9 eV

= 1.9 x 1.6 x 10^-19 J

λ₀ = {6.6 x 10^-34 Js x 3 x 10⁸ m/s}/{1.9 x 1.6 x 10^-19 J}

= 652 nm

(b) ϕ = hv₀

v₀ = ϕ/h = {1.9 x 1.6 x 10^-19}/{6.63 x 10^-34}

= 4.598 x 14 s^-1