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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?
A
Na only
B
Cs only
C
Both Na and K
D
K only
Explanation
Photoemission needs $\phi<2.20\ eV$; only caesium qualifies.
Detailed Solution
Incident energy $=2.20\ eV$
If $\phi2.20\ eV$: no electron emission.
Only caesium will emit electrons.