Q 12-11-045JEE MainJEE Main 2025 (22 Jan, Shift 1)Easy
The work functions of cesium (Cs) and lithium (Li) metals are $1.9\ \text{eV}$ and $2.5\ \text{eV}$, respectively. If light of wavelength $550\ \text{nm}$ is incident on these two metal surfaces, then photoelectric effect is possible for the case of
Answer: (C) Cs only
Photon energy:
$$E = \frac{hc}{\lambda} = \frac{1240\ \text{eV nm}}{550\ \text{nm}} \approx 2.25\ \text{eV}$$
Emission needs $E \ge \phi$: $2.25 > 1.9$ (Cs, yes) but $2.25 < 2.5$ (Li, no). So Cs only.
Solution by Sreeraj P, M.Sc Physics