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Metals like Li, Na, K and Cs are photosensitive even to visible light because they
A{'text': 'Have low work functions', 'label': 'A'}
B{'text': 'Have very high work functions', 'label': 'B'}
C{'text': 'Are magnetic materials', 'label': 'C'}
D{'text': 'Are all alkaline earth metals', 'label': 'D'}
Answer & Solution
Correct answer: A. {'text': 'Have low work functions', 'label': 'A'}
1. Alkali metals have loosely held valence electrons in the outermost shell.
2. Their work functions are low, of order 1-3 eV.
3. Visible light (1.7-3.1 eV) exceeds these work functions for many alkali metals.
4. So visible light can eject photoelectrons from Li, Na, K, Rb, Cs.
_Source: NCERT Class 12 Physics, Ch 11 "Dual Nature of Radiation and Matter", §11.3.2_
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