The Student Room Group

Thermistors - charge carriers?

I've been told that I need to include more detail in my report, on how thermistors work.

My thought was that the resistance of the metal thermistor is affected by the temperature, hence, the voltage/current changes etc - but apparently thats wrong.

He mentioned 'charge carriers', but I have no idea how to relate that to it....

Help?

Thanks :tsr: :biggrin:
Reply 1
The number of charge carriers (electrons) free to move in the thermistor varies with its temperature.
Reply 2
the drift velocity of the the charge carriers(electrons) slightly decrease in a thermistor as the tempreture increases but number of charge carriers increases significantly,so thats why their resistance decrease with the the increase of temperature and hence they conduct electricity you can use the equation I=nAvq for more explianation where n is number of charge carriers and v is the drift velocity and q is the charge of the electron A is the cross secotional area..hope that helps,I'm not that good in thermal physics but I think that was what is needed
Reply 3
Also note that the charge carriers may not neccessarily be electrons, they can just as likely be holes, yes HOLES. These are the absence of electrons, and in physics we treat this as a positively charged particle that moves through the latice. Read about the Hall probe to find out how they find out if electrons or holes conduct the electricity.
That should give you all the extra brownie point you need.

Also the drop in drift velocity is due to internal resistance. The kinetic energy in an electron can be worked out simply by multiplying its charge by the electric field that is acting on it (or the voltage across the thermistor). The drop in drift velocity is due to the drop in voltage drop across the thermistor. This effect of course is dependant completely on a large increase in current being drawn.
Given a voltage source (ie a battery with no internal resistance) being attached to the thermistor the drift velocity should stay the same.