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State working principle of photo diode. List out its three applications.

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Diagram of photo diode : 


Working principle of photo diode :  When photons of energy greater than 1.1 eV hit the diode, electron-hole pairs are created. The intensity of photon absorption depends on the energy of photons – the lower the energy of photons, the deeper the absorption is. This process is known as the inner photoelectric effect. If the absorption occurs in the depletion region of the p-n junction, these hole pairs are swept from the junction - due to the built-in electric field of the depletion region. As a result, the holes move toward the anode and the electrons move toward the cathode, thereby producing photocurrent. 

Applications principle of photo diode :  Cameras, Medical devices, Smoke detector, Optical communication devices, Position sensors, Bar code scanners, Automotive devices, Surveying instruments

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