A metal has a work function of $2.5\text{eV}$. Which of the following wavelengths of incident light can cause emission of electrons from its surface?

Step-by-step solution

1. Calculate the threshold wavelength using ${\lambda }_0=\frac{hc}{\varphi }$, where $hc=1240\text{eV⋅nm}$ and $\varphi =2.5\text{eV}$.
2. ${\lambda }_0=\frac{1240}{2.5}=496\text{nm}$.
3. Light with wavelength shorter than ${\lambda }_0$ has photon energy greater than the work function, so it can cause photoemission.
4. Among the given options, $450\text{nm}<496\text{nm}$, therefore it can eject electrons.
5. The other wavelengths (600, 500, 700 nm) are longer than ${\lambda }_0$ and will not cause emission.

Concept tested: Photoelectric effect – threshold wavelength

Published 7 September 2026 · How this solution was prepared and checked