PYQ NEET- Dual Nature Of Matter And Radiation L-2

Question: The work functions of Caesium $(\mathrm{Cs})$, potassium $(\mathrm{K})$ and Sodium $(\mathrm{Na})$ are $2.14 \mathrm{eV}, 2.30 \mathrm{eV}$ and $2.75 \mathrm{eV}$ respectively. If incident electromagnetic radiation has an incident energy of $2.20 \mathrm{eV}$, which of these photosensitive surfaces may emit photoelectrons?#

A) Both $\mathrm{Na}$ and $\mathrm{K}$ are alkali metals.

B) K only (K only)

C) $\mathrm{Na}$ only

D) Cesium only

Answer: Cs only#

Solution:#

Given energy of photon $E=2.20 \mathrm{eV}$

Work function of $\mathrm{Cs} \phi_0=2.14 \mathrm{eV}, \mathrm{K} \phi_0=2.30 \mathrm{eV}, \mathrm{Na} \phi_0=2.75 \mathrm{eV}$ We know that $e^{-}$ emits when $h v>\phi_0$ here it is clear that energy of photon is more than the work function of Cs [Caesium] only so Ans. only (Cs).