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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 Kmax as a function of the wavelength λ of the light falling on the surface of the metal. Which of  the following statements is/are correct?

  1. Threshold frequency for the metal is 1.2×1015Hz

  2. Work function of the metal is 4.968 eV.
  3. Maximum kinetic energy of photoelectrons corresponding to light of wavelength 100 nm is nearly 7.4 eV.
  4. Photoelectric effect takes place with red light.


Solution

The correct options are
A

Threshold frequency for the metal is 1.2×1015Hz


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.
KEmax is zero corresponding to λ = 250nm. Hence v=cf=3×108250×109=1.25×1015Hz
Work function (W) =1240λ(in nm)ev=4.96eV
For λ=100 nm; E=1240λ=124 ev.  HenceKEmax=12.44.967.4eV
Red light not cause photoelectric effect as the energy is very less.

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