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    Hi, I was wondering whether anyone could give me a simple (GCSE) explanation as to why the resistance of a thermistor decreases as the temperature increases? Thanks in advance
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    (Original post by VioletPhillippo)
    Hi, I was wondering whether anyone could give me a simple (GCSE) explanation as to why the resistance of a thermistor decreases as the temperature increases? Thanks in advance
    In a normal metallic conductor, increasing the temperature increases the resistance because the metallic ions in the lattice vibrate with more energy, which obstructs the free flow of electrons, hence causing a resistance. However, thermistors are made from semiconductors which behave differently. In a semiconductor, at low temperatures, there are barely any free charge carriers and hence a very low conductivity. As the temperature of the semiconductor is increases, charge carriers gain energy and some are 'promoted' to a higher energy level where they are free to move around. Simply, as the temperature of the semiconductor is increased, the number of free charge carriers and hence conductivity also increases.

    As the temperature increases, the ions or atoms in the semiconductor will also vibrate more vigerously (like in a metal) which will cause a resistance, but the effect of the increasing conductivity from the freed charge carriers is much bigger than the effect of increasing resistivity from the vibrating lattice so the overall effect is a decrease in resistance.
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    (Original post by Chlorophile)
    In a normal metallic conductor, increasing the temperature increases the resistance because the metallic ions in the lattice vibrate with more energy, which obstructs the free flow of electrons, hence causing a resistance. However, thermistors are made from semiconductors which behave differently. In a semiconductor, at low temperatures, there are barely any free charge carriers and hence a very low conductivity. As the temperature of the semiconductor is increases, charge carriers gain energy and some are 'promoted' to a higher energy level where they are free to move around. Simply, as the temperature of the semiconductor is increased, the number of free charge carriers and hence conductivity also increases.

    As the temperature increases, the ions or atoms in the semiconductor will also vibrate more vigerously (like in a metal) which will cause a resistance, but the effect of the increasing conductivity from the freed charge carriers is much bigger than the effect of increasing resistivity from the vibrating lattice so the overall effect is a decrease in resistance.
    Thank you, that was really helpful
 
 
 
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