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. 4eV
B. 6.2 eV
C. 2 eV
D. 2.2 eV

Answer

D

Explanation

The electrons ejected with maximum spedd `V_(max)` are stopped by electric field `E=(4N)/(C )` after traveling a distance `d=1 m`.
`(1)/(2)mv_(max)^(2)=eEd=4eV`
The energy of incident photon `=(1240)/(200)=6.2 eV`
From equation of photo electric effect
`(1)/(2)_(max)^(2)=hv-phi_0`
`phi_0=6.2-4=2.2eV`