In a photoelectric set-up, a point source of light (of power 3.2$\times$10^–3W) emits monoenergetic photons of energy 5.0 eV. The source is located at a distance of 0.8m from the centre of a stationary metallic sphere of work function 3.0 eV and of radius 8.0$\times$10^–3 m. The efficiency of photoelectric emission by the metallic sphere is one for every 10⁶ photons incident on it. Assume that the sphere is isolated and initially neutral, and the photo electrons emitted by it are instantly swept away. As a result of it, the sphere gets positively charged and acquires a positive potential and after a certain time the photoelectron emission from it stops. Take the energy reaching the sphere from the source of light per second to be $\mathrm{E}=\frac{{\mathrm{Pr}}^2}{4{\mathrm{R}}^2}$, where r is the radius of the sphere, R is the distance between the point source and the centre of the sphere and P is the power of the source.