Question

In a photoelectric effect experiment, the maximum kinetic energy of the ejected photoelectrons is measured for various wavelengths of the incident light. Figure shows a graph of this maximum kinetic energy $K_{max}$ as a function of the wavelength $\lambda$ of the light falling on the surface of the metal. Which of the following statements is/are correct?

• A. Threshold frequency for the metal is $1.2\times {10}^{15}Hz$
• B. Work function of the metal is 4.968 eV.
• C. Maximum kinetic energy of photoelectrons corresponding to light of wavelength 100 nm is nearly 7.4 eV.
• D. Photoelectric effect takes place with red light.

Answer 1

Answer: (A), (B), (C)

The correct options are
A

Threshold frequency for the metal is $1.2\times {10}^{15}Hz$

B Work function of the metal is 4.968 eV.
C Maximum kinetic energy of photoelectrons corresponding to light of wavelength 100 nm is nearly 7.4 eV.

$K{E}_{max}$ is zero corresponding to $\lambda$ = 250nm. Hence $v=\frac{c}{f}=\frac{3\times {10}^8}{250\times {10}^{-9}}=1.25\times {10}^{15}Hz$
Work function (W) $=\frac{1240}{\lambda \left(innm\right)}ev=4.96eV$
For $\lambda =100nm;E=\frac{1240}{\lambda }=124ev.HenceK{E}_{max}=12.4-4.96\simeq 7.4eV$
Red light not cause photoelectric effect as the energy is very less.