zhang17-2

zhang17-2 - r Linearly depends on T For most metals...

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1/26/2010 1 r Linearly depends on T For most metals, resistivity increases approximately linearly with temperature over a limited temperature range r : resistivity at temperature T ρ o : resistivity at reference temperature T o : temperature coefficient of resistivity )] ( 1 [ o o T T r

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1/26/2010 2 For most metals, resistivity increases with increasing temperature With a higher temperature , the metal’s constituent atoms vibrate with increasing amplitude More difficult for electrons to pass through because electrons will bump into atoms more frequently The amplitude of vibration increases with increasing temperature, more difficult for electrons to pass through For semiconductors and insulators , it is quite the opposite: Resistivity decreases with increasing temperature In these materials, electrons are not able to move freely at zero temperature The higher the temperature, the more electrons can move freely resistivity decreases with increasing T
1/26/2010 3 Positive for metals Negative for semiconductors and insulators T-dependence of resistivity results in T-dependent resistance Let )] ( 1 [ 0 o T T R R 0 0 0 ture at tempera resistance the : T A l R r )] ( 1 [ o o T T A l R R l T T R o o )] ( 1 [ )] ( 1 [ o o T T R l R

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1/26/2010 4 Right after the switch is closed, the filament is cold (room temperature). At low T, R is small Small R large current I, i.e., a current spike right after the switch is closed
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zhang17-2 - r Linearly depends on T For most metals...

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