Mavs04
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Hi, I’m a bit confused about why the resistance of a filament lamp increases with current (and therefore with temperature).

I know that the current can be the flow of any charged particle, like through a metal it’s the delocalised electrons or through a molten/aqueous ionic compound it’s the ions, but through a filament lamp is the current the flow of delocalised of electrons or the flow of metal ions - I’m pretty sure the metal ions aren’t free to move (apart from vibrations) - but just checking lol.

But if this is true then I’m really confused about how it’s possible that the resistance of an nct thermistor decreases as temperature increases! 😭

Ty!
Last edited by Mavs04; 4 months ago
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uberteknik
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(Original post by Mavs04)
Hi, I’m a bit confused about why the resistance of a filament lamp increases with current (and therefore with temperature).

I know that the current can be the flow of any charged particle, like through a metal it’s the delocalised electrons or through a molten/aqueous ionic compound it’s the ions, but through a filament lamp is the current the flow of delocalised of electrons or the flow of metal ions - I’m pretty sure the metal ions aren’t free to move (apart from vibrations) - but just checking lol.

But if this is true then I’m really confused about how it’s possible that the resistance of an nct thermistor decreases as temperature increases! 😭

Ty!
The atoms in a conductor are fixed and electrons delocalise, as you say, with increasing temperature. However, the fixed atoms gain vibrational energy. This also means more atomic collisions occur to capture free electrons and thus making it more difficult for them to move through the structure. i.e. resistance increases with temperature.

NTC Thermistors are constructed from semiconductor materials where covalent bonds dominate the atomic structure. Outer (valance) band electrons are shared and bonds are formed between three, four or five atoms. As temperature increases, electrons from lower energy bands gain energy and are promoted to the outer valence (conduction) band. NB the electrons are not delocalised but hop between shared bond atoms. More electrons for conduction are then available for conduction through that valence band electron sharing. i.e. More valence electrons = more available to migrate = greater current and hence resistance decreases with increasing temperature.
Last edited by uberteknik; 4 months ago
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