A transparent quartz window is sealed on to the glass
tube, which permits ultraviolet radiation to pass through it and irradiate
the photosensitive plate C The electrons are emitted by the plate C and
are collected by the plate A (collector), by the electric field created by the
battery The battery maintains the potential difference between the plates
C and A, that can be varied The polarity of the plates C and A can be
reversed by a commutator