Give the construction and working of photo emissive cell.

Explanation

Construction:
(i) Photo emissive cell consists of an evacuated glass or quartz bulb in which two metallic electrodes – that is, a cathode and an anode are fixed.
(ii) The cathode C is semi-cylindrical in shape and is coated with a photo sensitive material.
(iii) The anode A is a thin rod or wire kept along the axis of the semi-cylindrical cathode.
(iv) A potential difference is applied between the anode and the cathode through a galvanometer G.

Working:
When cathode is illuminated, electrons are emitted from it. These electrons are attracted by anode and hence a current is produced which is measured by the galvanometer. For a given cathode, the magnitude of the current depends on
(i) the intensity to incident radiation and
(ii) the potential difference between anode and cathode.