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Topic: Photoelectric effect, Hertz and Lenard's observations· Dual Nature of Matter and Radiation

The work functions of Caesium (Cs), Potassium (K) and Sodium (Na) are 2.14 eV, 2.30 eV and 2.75 eV respectively. If incident electromagnetic radiation has an incident energy of 2.20 eV, which of these photosensitive surfaces may emit photoelectrons?

1. Na only

2. Cs only

3. Both Na and K

4. K only

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Answer: 2. Cs only

A surface emits photoelectrons only if the photon energy is at least its work function.

  • Cs: \(2.20 \ge 2.14\) eV, so it emits.
  • K: \(2.20 < 2.30\) eV, no emission.
  • Na: \(2.20 < 2.75\) eV, no emission.

Only caesium emits photoelectrons, so the answer is Cs only.

Doubtly AI · 30 Oct 2026 AI-generated · not yet verified Report
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