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All electrons ejected from a surface by incident light of wavelength 200 nm can be stopped before travelling 1 m in the direction of uniform electric field of 4 N/C. The work function (in eV) of the surface is:  

Option: 1 4

Option: 2 6.2

Option: 3 2

Option: 4 2.2

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The electron ejected with maximum speed  v_{max}  are stopped by electric field E = 4N/C after travelling a distance d = 1m

\therefore \frac{1}{2}mv_{max}^2=eE d=4eV

The energy of incident photon =\frac{1240}{200}=6.2eV

From equation of photo electric effect

\frac{1}{2}mv_{max}^2=hv-\phi_{0}

\therefore \phi_{0}=6.2-4=2.2eV

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avinash.dongre

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