Work functions of Cs, K and Na are respectively 2.14 eV, 2.30 eV and 2.75 eV. A radiation of photon energy 2.20 eV is incident. Which surface may emit electrons?
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Question

Work functions of Cs, K and Na are respectively 2.14 eV, 2.30 eV and 2.75 eV. A radiation of photon energy 2.20 eV is incident. Which surface may emit electrons?

G1 Physics · Accepted Answer

Emission requires Eγ ≥ W. Compare 2.20 eV to each work function: 2.20 > 2.14 for Cs, but 2.20 < 2.30 and 2.75 for K and Na. Thus only Cs emits. Answer: C.