Question

Light of wavelength 4000 $\mathring{A}$ is incident on a metal surface. The maximum kinetic energy of emitted photoelectron is 2 eV. What is the work function of the metal surface?

• A. 4 eV
• B. 1 eV
• C. 2 eV
• D. 6 eV

Answer 1

Answer: (B)

1 eV

Work function is the minimum energy required by an electron to just escape from the metal surface as to overcome the restraining forces at the surface of metal.

According to Einstein's photoelectric equation the work function of metal is given by :

$\therefore \varphi =\frac{hc}{\lambda }-K{E}_{max}$

$=\frac{6.6\times {10}^{-34}\times 3\times {10}^8}{4000\times {10}^{-10}}-2eV$

$=4.95\times {10}^{-19}-2eV$

$=\frac{495\times {10}^{-19}}{1.6\times {10}^{-19}}-2eV$

$=3eV-2eV=1eV$