Question

Explain the working of a photo emissive cell. Write any two applications of photo electrics cells.

Answer 1

Hint:Photo-emissive cells are based on the principle of photoelectric effect. The phenomenon in which electrically charged particles are released from or within a material when it absorbs electromagnetic radiation. Construction and Working are being explained in the complete solution below.

Complete step by step answer:
Firstly, knowing definition for Photoelectric cell or photocell is an electronic device which works on the principle of the photoelectric effect and converts light energy into electrical energy.Photo emissive cells are the oldest way of turning light into electricity.

Now, Construction of photo-emissive cell: -
It consists of evacuated glass or quartz bulbs in which there are two metallic electrodes that are anode and cathode. The cathode C is semi-cylindrical in shape and is coated with photosensitive material and anode A is a thin rod or wire kept along the axis of semi-cylindrical cathode. The potential difference is applied across cathode and anode through the galvanometer.

Working of photo-emissive cell: -
When the electrons are emitted, anode will attract that electrons and the current will start moving which is measured by the galvanometer. The current produced will depend on intensity of the incident radiation and the potential difference across the cathode and anode.

Applications:
Used for controlling the temperature of the furnace. Used for automatic switching on and off of street bulbs. And for reproducing sound in cinematography.

Note:Photo emissive cells are small, inexpensive, low power, easy to use and don’t wear out. Phototube and photoelectric cells are the same as photo emissive cells but photovoltaic and photoconductive cells are different. The bulb of the cells is filled with an inert gas like helium, neon, argon etc.