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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?

A

Threshold frequency for the metal is 1.2×1015Hz

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B
Work function of the metal is 4.968 eV.
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C
Maximum kinetic energy of photoelectrons corresponding to light of wavelength 100 nm is nearly 7.4 eV.
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D
Photoelectric effect takes place with red light.
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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=3×108250×10−9=1.25×1015Hz Work function (W) =1240λ(in nm)ev=4.96eV For λ=100 nm; E=1240λ=124 ev. HenceKEmax=12.4−4.96≃7.4eV Red light not cause photoelectric effect as the energy is very less.

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