Radiation of intensity` 0.5 xx 10^-4 W//m^2` falls on the emitter in a photoelectric set-up. The emitter (cathode) is made up of potassium and has an area of` 5 cm^2`. Let us assume that the electrons from only the surface are knocked off by the radiation. According to the wave theory,what will be the time required to notice some deflection in the microammeter connected in the circuit? (Given the metallic radius of potassium atom is 230 pm and work function of potassium is 2.3 eV.)