P. 4182. A pointlike discharge lamp of power 5 W emits monochromatic light of wavelength 425 nm. The cathode of a photocell is placed 1 m from the light source, perpendicularly to the light rays. The radius of the cathode is 0.5 cm and the work function of its material is 2.10-19 J. A capacitor of capacitance 2 nF is connected to the anode and the cathode of the photocell.
a) What is the energy of one photon emitted by the discharge lamp? How many photons hits the cathode of the photocell in each second?
b) What is the maximum of the speed of the electrons which leaves the cathode?
c) What will the voltage of the capacitor be?