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JEE Advanced 2022 Paper 1 · Physics · Atoms, Nuclei and Dual Nature of Radiation · hard

Light of wavelength 300 nm falls on a metal of work function 2.0 eV. Use hc=1240 eV nm.

One or more options correct

Light of wavelength 300 nm300\ \mathrm{nm} falls on a metal of work function 2.0 eV2.0\ \mathrm{eV}. Use hc=1240 eV nmhc=1240\ \mathrm{eV\,nm}. Choose the correct option(s).
  1. A. The stopping potential is about 2.13 V2.13\ \mathrm{V}.
  2. B. Doubling the intensity doubles the stopping potential.
  3. C. The threshold wavelength of the metal is 400 nm400\ \mathrm{nm}.
  4. D. If the frequency of the light is halved, photoelectric emission stops.
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Answer: A

Photon energy =1240/300=4.13 eV=1240/300=4.13\ \mathrm{eV}, so eVs=4.13−2.0=2.13 eVeV_s=4.13-2.0=2.13\ \mathrm{eV}: (A) true. Stopping potential depends on frequency, not intensity: (B) false. Threshold wavelength =1240/2.0=620 nm=1240/2.0=620\ \mathrm{nm}, not 400 nm400\ \mathrm{nm}: (C) false. Halving the frequency gives photon energy 2.07 eV>2.0 eV2.07\ \mathrm{eV}>2.0\ \mathrm{eV}, so emission still occurs (with tiny kinetic energy): (D) false.
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