A point source of light emits photons of energy $4.8 \mathrm{eV}$ at the rate $10^5$ photons per second.…
A point source of light emits photons of energy $4.8 \mathrm{eV}$ at the rate $10^5$ photons per second. These photons incident on a photo-sensitive sphere of work function $2.8 \mathrm{eV}$ and radius $9 \mathrm{~mm}$. The sphere is initially neutral and the emitted photo electrons are instantly swept away. The time after which the photo electric emission stops is