Question

Give the construction and working of photo emissive cell.

Answer 1

Photo emissive cell: Its working depends on the electron emission from a metal cathode due to irradiation of light or other radiations.

Construction:

1. It consists of an evacuated glass or quartz bulb in which two metallic electrodes – that is, a cathode and an anode are fixed.

2. The cathode C is semi-cylindrical in shape and is coated with a photo sensitive material. The anode A is a thin rod or wire kept along the axis of the semi-cylindrical cathode.

3. A potential difference is applied between the anode and the cathode through a galvanometer G.

Construction of photo cell

Working:

When the cathode is irradiated with suitable radiation, electrons are emitted from it. These electrons are attracted by the anode and hence a current is produced which is measured by the galvanometer.

For a given cathode, the magnitude of the current depends on

1. the intensity to incident radiation and
2. the potential difference between anode and cathode.