activation energy [Archive]

Rose Mary Chacko

May26-04, 05:12 AM

William R. Frensley

May26-04, 01:56 PM

<jabberwocky><div class="vbmenu_control"><a href="jabberwocky:;" onClick="newWindow=window.open('','usenetCode','toolbar=no, location=no,scrollbars=yes,resizable=yes,status=no ,width=650,height=400'); newWindow.document.write('<HTML><HEAD><TITLE>Usenet ASCII</TITLE></HEAD><BODY topmargin=0 leftmargin=0 BGCOLOR=#F1F1F1><table border=0 width=625><td bgcolor=midnightblue><font color=#F1F1F1>This Usenet message\'s original ASCII form: </font></td></tr><tr><td width=449><br><br><font face=courier><UL><PRE>\nRose Mary Chacko wrote:\n> Could anyone tell me what is the meaning of activation energy in a thermistor?\n\nIf an activation energy is quoted for a thermistor, it is presumably a negative\ntemperature coefficient type that uses a doped semiconductor to sense the\ntemperature. The semiconductor has a band of states that permits electrons to\nflow so as to conduct current, and a number of localized states at a lower\nenergy which immobilize any electrons residing in them. The difference between\nthese levels is the activation energy. The temperature dependence arises\nbecause the conductance (reciprocal of the resistance) is proportional to\nthe number of electrons in the conduction band. This number is in turn\nproportional to a Boltzmann factor of the form exp[-(activation energy)/kT],\nwhere kT is Boltzmann\'s constant times the absolute temperature.\nkT = 0.0259 eV at T=300K. With this information, you can calculate the\ntemperature coefficient of the thermistor.\n\n- Bill Frensley\n\n</UL></PRE></font></td></tr></table></BODY><HTML>');"> <IMG SRC=/images/buttons/ip.gif BORDER=0 ALIGN=CENTER ALT="View this Usenet post in original ASCII form">  View this Usenet post in original ASCII form </a></div><P></jabberwocky>Rose Mary Chacko wrote:
> Could anyone tell me what is the meaning of activation energy in a thermistor?

If an activation energy is quoted for a thermistor, it is presumably a negative
temperature coefficient type that uses a doped semiconductor to sense the
temperature. The semiconductor has a band of states that permits electrons to
flow so as to conduct current, and a number of localized states at a lower
energy which immobilize any electrons residing in them. The difference between
these levels is the activation energy. The temperature dependence arises
because the conductance (reciprocal of the resistance) is proportional to
the number of electrons in the conduction band. This number is in turn
proportional to a Boltzmann factor of the form \exp[-(activation energy)/kT],
where kT is Boltzmann's constant times the absolute temperature.
kT = .0259 eV at T=300K. With this information, you can calculate the
temperature coefficient of the thermistor.

- Bill Frensley