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 Form 4 Physics Photoelectric effect online video lessons

Applications of photoelectric effect

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Answer Text:
Applications of photoelectric effect
-Photo-emissive cells– they are made up of two electrodes enclosed in a glass bulb (evacuated or containing inert gas at low temperature). The
cathode is a curved metal plate while the anode is normally a single metal rod)
figphotoeletriceffect25820201514.JPG
-They are used mostly in controlling lifts (doors) and reproducing the sound track in a film.
-Photoconductive cells – some semi-conductors such as cadmium sulphide (cds) reduces their resistance when light is shone at them (photo
resistors). Other devices such as photo-diodes and phototransistors block current when the intensity of light increases.
-Photo-conductive cells are also known as light dependent resistors (LDR) and are used in alarm circuits i.e. fire alarms, and also in cameras as exposure metres.
figphotoeletriceffect25820201515.JPG
-Photo-voltaic cell– this cell generates an e.m.f using light and consists of a copper disc oxidized on one surface and a very thin film of gold is
deposited over the exposed surfaces (this thin film allows light). The current increases with light intensity.
figphotoeletriceffect25820201516.JPG
They are used in electronic calculators, solar panels etc.


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