Question

All electrons ejected from a surface by incident light of wavelength 200 nm can be stopped before traveling 1 m in the direction of a uniform electric field of4NC-1. The work function of the surface is

Answer 1

The work function of the surface is 2.2 eV

Explanation :

The electron ejected with speed V can be stopped by the electric field

Hence  KE of the electron = work done by the force field

=> mv²/2 = e x E x d

E = 4 N/c and d = 1 m

=>  mv²/2 = 4 eV

The wavelength of the incident light = 200 nm

=> Energy of the incident photon, hv₀ = 1240/200 = 6.2 eV

From the photo electric effect equation we know that,

mv²/2 = hv₀ - Ф₀

=>  Ф₀ = hv₀ - mv²/2

= 6.2 - 4

=> Ф₀ = 2.2 eV

Hence the work function of the surface is 2.2 eV