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  1. 1. current-voltage characteristicsof a CdS photo resistor
  2. 2. • Mohammad abdalraheem• Edward nixson• Awad osman• Mohammed abdala• Osman salah
  3. 3. Objects of theexperiments Measuring the photocurrent I Ph as a function of the voltage U at a constant irradiance . Measuring the photocurrent I Ph as a function of the irradiance at a constant voltage U.
  4. 4. Photocurrent ? a stream of electrons released froma photoelectric cell by the action oflight.
  5. 5. CONTENTS : Introduction photoresistor Current–voltage characteristic Polarization of light Setup Mechanism of photo resistor Result Conclusion
  6. 6. Introduction: A photoresistor is made of a high resistance semiconductor. depends on the amount of light incident upon it. Photo resistors are:used to make light-sensitive devices often made from cadmium sulfide (CdS).
  7. 7.  The resistance of a CdS photoresistor varies inversely to the amountof light incident upon it. Its resistance will be higher at lowlight levels (in the dark) and lower athigh light levels (in the light).
  8. 8.  Cadmium sulfide is the inorganic compound withthe formula CdS. It occurs in nature with two different crystalstructures. As a compound that is easy to isolate and purify, it is the principal source of cadmium for allcommercial applications.
  9. 9. The photoresistor
  10. 10. IRRADIANCE Is the power of electromagneticradiation per unit area (radiation flux )of a surface.
  13. 13.  Model of an ideal photoconductor: electron-hole pairs are produced throughout the crystal by theexternal light source and undergo recombination.Electrons leaving the crystal at the electrode (+) arereplaced with electrons entering at the electrode (-).
  14. 14. D : transparency when thepolarization planes areparallelØ : The irradianceØ 0: irradiance withoutpolarization filterscos2∞: the anglebetween the polarizer
  15. 15. The CdS photo resistor behaves like an ohmicresistance that depends on the irradiance.The photocurrent I ph as a function of thevoltage u at constant irradiance was measuring.The photocurrent I ph as a function of theirradiance at constant voltage u was measuring.