Physics Stack Exchange is a question and answer site for active researchers, academics and students of physics. It's 100% free.

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

Surely, upon an increase in temperature, the atoms within the thermistor would vibrate with more energy and therefore more vigorously, hence making the electrons flowing through the electric circuit more likely to collide with one of the atoms, so increasing resistance.

However, the effect of temperature on a thermistor is contrary to this. I can't understand how it can be.

It's analogous to running across a playground: if everyone is still you're less likely to collide with someone, however if everyone is constantly moving from left to right then a collision is more likely.

So why does an increase in temperature decrease the resistance of a thermistor?

share|cite|improve this question
up vote 8 down vote accepted

Thermistor with this particular temperature behavior are commonly semiconductors. In a semi-conductor, there is an energy gap between the (filled) valence and the (empty) conduction band. At zero temperature, no charges are in the conduction band and the resistance should be infinite as the system behaves basically like an insulator.

If you turn on the temperature, some electrons will start to occupy the conduction band and thus contribute to conduction, lowering the resistivity.

share|cite|improve this answer

Using your playground example....

Imagine if you had to pass a message (electricity) across the playground, when cold you would have to stretch between each fixed person to pass this message. When hot, more people fill the gaps, the message is easier to pass.

Hope this helps :)

share|cite|improve this answer

Olly, the first part of your thinking is correct, as the atoms receive more energy, the electrons do collide more energetically, but they also move "away" from the atom's center. The further they are from the center, the easier it is for an electric field to "move" them. This means that for the same effort (voltage), more electrons are moved (larger current). Since R = E/I, the effective resistance decreases as the current increases (for the same voltage).

share|cite|improve this answer

protected by Community Oct 3 '14 at 11:06

Thank you for your interest in this question. Because it has attracted low-quality or spam answers that had to be removed, posting an answer now requires 10 reputation on this site.

Would you like to answer one of these unanswered questions instead?

Not the answer you're looking for? Browse other questions tagged or ask your own question.