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PHOTOELECTRIC CELL

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A photocell or photoelectric cell is a device in which light energy is converted into electrical energy by photoelectric effect.
Constuction : A photoelectric cell as shown in the figure consists of a sealed glass tube enclosing as emitter (cathode) and a collector (anode). The cell is either highly evacuated (for accurate photomety) or filled with an inert gas at low pressure (if larger current is desired). The light enters through a quartz window W and falls on the semicylindrical cathode C coated with a photosensitive metal. The anode is in the form of straight wire of plantinum or nickel, coaxial with the cathode. For visible light, the cathode is coated with potassium or rubidium and the quartz window is replaced by a glass window. If only UV radiation is to be used., cadmium is used as the sensitive surface.
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Photoelectric Effect|Photoelectric Equation|Explanation For Photoelectric Effect|Summary

Knowledge Check

  • Assertion: K and Cs are sued in photoelectrical cells. Reason: K and Cs emit electrons on exposure to light.

    A
    if both assertion and reason are true and the reason is the correct explanation of the assertion.
    B
    If both assertion and reason are true but reason is not the correct explanation of the assertion.
    C
    If assertion is true but reason is false
    D
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  • When a monochromatic point source of light is at a distance of 0.2 m from a photoelectric cell, the cut-offf voltage and the saturation current are respectively 0.4 V and 12 mA. If the same source is placed 0.4 m away from the photoelectric cell, then

    A
    the stopping potential will be 0.2 V
    B
    the stopping potential will be 0.6 V
    C
    the saturation current will be 4.0 mA
    D
    the saturation current will be 3 mA

  • when a monochromatic point source of light is at a distance 0.2 m from a photoelectric cell, the saturation current and cut-off voltage are 12.0 mA and 0.5 V. If the same source is placed 0.4 m away from the photoelectric cell, then the saturation current and the stopping potential respectively are

    A
    4 mA and 1 V
    B
    12 mA and 1 V
    C
    3 mA and 0.5 V
    D
    12 mA and 0.5 V

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