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A metal surface with work function phi = 2.1 eV is irradiated with photons of energy 4.0 eV. What is the maximum kinetic energy of the photoelectrons emitted?
- 2.1 eV
- 4.0 eV
- 1.9 eV
- 6.1 eV
Correct answer: 1.9 eV
Solution
By Einstein's photoelectric equation, the maximum kinetic energy of an emitted photoelectron equals the incident photon energy minus the work function of the metal. KE_max = E_photon - phi = 4.0 eV - 2.1 eV = 1.9 eV. The work function 2.1 eV is the energy required to release an electron from the surface; the excess 1.9 eV appears as kinetic energy.
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