This is one of the most important rather interesting aspect of photoelectricity where photoelectric emission can be made use of,in innumerable devices depending upon human skill,imagination and ability to control this phenomena.Applications that make our life more meaningful .you come across many devices everyday that uses the knowledge of photoelectric effect but you just don't know.Let me give you an insight:-
- Television transmission-television camera makes use of this principle and thus bright and dark light images are interpreted as high and low electrical charges because of photoelectric emission .This are further processed and television signals are telecast.
- Astronomy-light from the stars are too weak to be analysed but good enough to fall on the cathode of photoelectric cells and eject electrons whose energies and intensities are interpreted as temperature and intensities of those stars.
- Temperature control-let us suppose that we want to control the temperature of the furnace .For this setup we will need a photoelectric cell and a relay.When the temperature increases,more intense radiation falls on the photocell and then the relay operates the no switch which in turn cuts off the power supply and when temperature falls vice-versa happens.You can make use of this kind of setup in fridges and geysers.But currently I think they use thermoswitches for this kind of operation.
- Automatic fire alarm-smoke sensors in offices and malls make use of photoelectric cells where there is a fire risk.When fire breaks out it illuminates the cathode of the cell.This coupled with the relay operates the yes switch and rings the fire alarm.
- Automatic burglar alarm-A source of ultraviolet radiation is focussed on the cathode of photoelectric cell with relay.The moment a thief comes in the radiation is cut off and relay operates the no switch and automatically rings the bell and puts on the lights in the house.
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