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    For lamp:
    Increased atomic vibrations due to a higher temperature reduce the movement of electrons
    Resistance of lamp increases with temperature

    For thermistor
    Increased atomic vibrations from a higher temperature again reduce movement of electrons
    But increase in temperature leads to a large increase in n in I=nAvq
    Overall the resistance of the thermistor decreases with a higher temperature.

    My question is WHY can't you say the bold point for the lamp as well as the thermistor?
    Thanks
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    (Original post by krisshP)
    For lamp:
    Increased atomic vibrations due to a higher temperature reduce the movement of electrons
    Resistance of lamp increases with temperature

    For thermistor
    Increased atomic vibrations from a higher temperature again reduce movement of electrons
    But increase in temperature leads to a large increase in n in I=nAvq
    Overall the resistance of the thermistor decreases with a higher temperature.

    My question is WHY can't you say the bold point for the lamp as well as the thermistor?
    Thanks
    Put simply...
    In the metal in the lamp, all the available electrons can already take part in conduction.

    In the semiconductor thermistor only a fraction of the electrons can take part in conduction.

    Heating the semiconductor produces more electrons that can take part in conduction, reducing the resistance.
    In the metal, increasing its temperature does not increase the number of available electrons. They were all available to begin with.

    http://en.wikipedia.org/wiki/Conduction_band
    http://hyperphysics.phy-astr.gsu.edu...lids/band.html
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    (Original post by Stonebridge)
    Put simply...
    In the metal in the lamp, all the available electrons can already take part in conduction.

    In the semiconductor thermistor only a fraction of the electrons can take part in conduction.

    Heating the semiconductor produces more electrons that can take part in conduction, reducing the resistance.
    In the metal, increasing its temperature does not increase the number of available electrons. They were all available to begin with.

    http://en.wikipedia.org/wiki/Conduction_band
    http://hyperphysics.phy-astr.gsu.edu...lids/band.html
    So in the filament of a lamp, inside the metal, all the ions have already completely lost all of their electrons. So the number of free electrons already is at a maximum in the metal. Heating the filament has no effect on the number of free electrons as the atoms have already released all of their electrons. Thermal excitation of the ions is not possible. However in the thermistor all ions have lost no electrons, so thermal excitation of atoms is possible. When heating the thermistor more electrons become free to carry the charge, so current increases.

    Is this right?
    Thanks a ton.
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    (Original post by krisshP)
    So in the filament of a lamp, inside the metal, all the ions have already completely lost all of their electrons. So the number of free electrons already is at a maximum in the metal. Heating the filament has no effect on the number of free electrons as the atoms have already released all of their electrons. Thermal excitation of the ions is not possible. However in the thermistor all ions have lost no electrons, so thermal excitation of atoms is possible. When heating the thermistor more electrons become free to carry the charge, so current increases.

    Is this right?
    Thanks a ton.
    That's about it. Yes.
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    (Original post by stonebridge)
    that's about it. Yes.
    thanks!!!
 
 
 

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