All electrons ejected from a surface by incident light of wavelength 200nm can be stopped before traveling 1m in the direction of a uniform electric field of `4 NC^(-1)`. The work function of the surface is

Options

A. 4e V
B. 3.2 eV
C. 6.2 eV
D. 2.2 eV

Answer

B

Explanation

The electron ejected with maximum speed `v_(max)` are stopped by electric field E = 6 N/C after travelling a distance d=1 m
`therefore mv_(max)^(2) =eEd = 3eV`
Ther energy of incident photon `=(1240)/(200)` = 6.2 eV
From equation of photo electric effect `1/2 mv_(max)^(2) = h upsilon - phi_0`
`Therefore phi_0 =6.2-3 = 3.2 eV`.