Physics - Semiconductors Question with Solution | TestHub

The wavelength corresponding to $2.5\mathrm{eV}$ is given by Energy $(\mathrm{eV})=\frac{12400}{\lambda (\mathring{A})}$ $$\therefore \lambda =\frac{12400}{2.5}=5000\mathring{A}$$ To get detected, the signal should have energy greater than $2.5\mathrm{eV}$ or wavelength less than $5000\mathring{A}$.