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Answer the following questions: Light of wavelength 5000 A propagating in air gets partly reflected from the surface of water. How will the wavelengths and frequencies of the reflected and refracted light be affected ? |
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Answer» SOLUTION :A photodiode (for special purpose) is fabricated with a transparent window to allow light to fall on the junction of the diode. When the junction of photodiode is reverse bias it is ILLUMINATED with light of energy `hv gt E_(g)` of the semiconductor, the ELECTRON-hole pairs are generated due to absorption of photon. Due to electric field of the function, electron are collected in n side and holes are collected on p-side and PRODUCES an emf. When an external load is connected, an electric current flows in the external circuit. The magnitude of the electric current depends on the intensity of incident light. Reason of Reverse Biasing : If there is no illumination, majority electrons are more than minority holes in n region of the diode. On illumination the junction, some electrons-hole pairs are generated. Let the excess electrons and holes generated are DN and Dp respectively So. at a particular illumination, `n'=n+Delta n` and`p'=p+Delta p` Since, `Delta n = Delta p` and `n gt p` Hence, `= (Delta n)/(n) lt lt (Delta P)/(P)` It means the minority carriers dominated reverse bias current is more easily measurable, than change in the forward bias current. Hence, photodiodes are preferably used in the reverse bias light intensity. 
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