The work functions of Caesium (Cs), Potassium (K) and Sodium (Na) are 2.14 eV, 2.30 eV and 2.75 eV respectivel

Question

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?

Accepted Answer

Photoelectric emission occurs only if the incident energy $E$ is greater than or equal to the work function $\phi$ of the metal. Given $E = 2.20$ eV. For Cs, $\phi = 2.14$ eV. Since $2.20 > 2.14$, Cs will emit photoelectrons. For K, $\phi = 2.30$ eV and for Na, $\phi = 2.75$ eV. Since $2.20 < 2.30$ and $2.20 < 2.75$, neither K nor Na will emit photoelectrons.

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