The surface of a metal is illuminated with light of 400 nm. The kinetic energy of the ejected photoelectrons was found to be 1.68 eV. The work function of the metal is: (hc = 1240 eV.nm)
Correct answer: B. 1.41 eV
- A. 3.09 eV
- B. 1.41 eV
- C. 1.51 eV
- D. 1.68 eV
Explanation
Photon energy E = hc/λ = 1240/400 = 3.1 eV. Kinetic energy KE = 1.68 eV. Work function Φ = E - KE = 3.1 - 1.68 = 1.42 eV ≈ 1.41 eV.
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About Dawn of Modern Physics
Classical physics cannot explain blackbody radiation and related observations, leading to Planck’s quantum theory, in which energy is emitted or absorbed in discrete packets. Photons provide the particle model of light, with energy and momentum linked to frequency and wavelength, including the photoelectric effect and its threshold frequency.
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