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When the energy of the incident radiation is increased by 20%, the kinetic energy of the photoelectrons emitted from a metal surface increased from 0.5 eV to 0.8 eV. The work function of the metal is

1. 0.65 eV
2. 1.0 eV
3. 1.3 eV
4. 1.5 eV

Correct answer: 0.65 eV

Solution

The photoelectric equation is given by: K.E. = hν - φ, where φ is the work function. Initially, hν = K.E. + φ = 0.5 + φ. When hν increases by 20%, the new energy is 1.2hν, and the new K.E. is 0.8 eV. Substituting, 0.8 = 1.2hν - φ. Solving these equations gives φ = 0.65 eV.

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