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 of 4NC-1. The work function of the surface is

The electrons ejected with maximum speed Vmax are stopped by electric field E=4N/C after traveling a distance d=1 m.12mvmax2=eEd=4eV The energy of incident photon =1240200=6.2eVFrom equation of photo electric effect12mvmax2=hv−ϕ0∴ϕ0=6.2−4=2.2eV