First slide

Photoelectric effect and study of photoelectric effect

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

Moderate

A

4eV
B

6.2eV
C

2eV
D

2.2eV

Solution

The electrons ejected with maximum speed V_maxare stopped by electric field E=4N/C after traveling a distance d=1 m.
$\frac{1}{2} m v_{max}^{2} = e E d = 4 eV$
$The energy of incident photon = \frac{1240}{200} = 6.2 eV$
From equation of photo electric effect
$\begin{array}{l} \frac{1}{2} m v_{max}^{2} = h v - ϕ_{0} \\ ∴ ϕ_{0} = 6.2 - 4 = 2.2 eV \end{array}$

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