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Which of these emission processes does NOT depend on a threshold frequency of incident radiation?
A{'text': 'Thermionic emission', 'label': 'A'}
B{'text': 'Photoelectric emission', 'label': 'B'}
C{'text': 'Emission from cold cathode by ultraviolet light', 'label': 'C'}
D{'text': 'Photoemission from a caesium cell', 'label': 'D'}
Answer & Solution
Correct answer: A. {'text': 'Thermionic emission', 'label': 'A'}
1. Thermionic emission is caused by heating the metal to give electrons enough thermal energy.
2. It does not require any incident light and has no threshold frequency.
3. Photoelectric emission requires ν ≥ ν₀ (threshold frequency) to occur.
4. Field emission requires a large electric field, not a specific light frequency.
_Source: NCERT Class 12 Physics, Ch 11 "Dual Nature of Radiation and Matter", §11.2_
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