JEE Main · 2006 · 30 Apr 2006 · Offline · Modern Physics

With the anode voltage held fixed, the photocell passes current only when the incident light can eject electrons, which requires the photon energy to exceed the work function, i.e. the wavelength to be below the threshold ${\lambda }_0$. For $\lambda <{\lambda }_0$ electrons are emitted and a current flows; as the wavelength is raised past ${\lambda }_0$ the photon energy drops below the work function and the current falls to zero. The correct graph is the one that shows a non-zero plate current for wavelengths below ${\lambda }_0$, vanishing once $\lambda$ exceeds ${\lambda }_0$.