Thermo E.M.F.
by
J. K. Mishra
Email : j.k.mishra@poornima.org
OUTLINE

Thermoelectric Effects

Seeback coefficient

Experimental arrangement

Applications
2
SEEBECK EFFECT

In 1821, Thomas Seebeck found that an electric
current would flow continuously in a closed circuit
made up of two different metals, if the junctions of
the metals were maintained at two different
temperatures.
S= dV / dT;
S is the Seebeck Coefficient with units of Volts per Kelvin
S is positive when the direction of electric current is same
as the direction of thermal current
3
THERMOELECTRIC EFFECT
Electrically conductive material exhibit three
types of thermoelectric phenomena
 Seeback effect
 Peltier effect
 Thomson effect
4
5
And there it glows
SEEBECK EFFECT
voltmeter
V
V

T
Hot
Cold
Two different metals
6
SEEBECK EFFECT
The Seebeck effect is the conversion of
temperature difference directly into electricity.
 It is named after German Physicist Thomas
Johann Seebeck.
 In 1821, he discovered that a compass needle
would be deflected by a closed loop formed by
two metals joined in two places with
temperature difference between two junctions.
 This was because the metals responded
differently to the temperature difference
creating a current loop and magnetic field.

7
Seebeck
Thermomagnetic effect
Danish Physicist Hans Christian Oersted rectified the mistake
and coined the term “Thermoelectricity”
TC
TH
++
--
V
TC
TH
e8
I
CAUSE OF SEEBECK EFFECT
 Number density of e- varies for different metals
 At the junction
to another.
e- migrate from one metal
 It sets up an opposing electric field.
 As a result potential difference is developed.
9
This effect is called Seebeck effect
This combination of two metals in such a
manner is called “Thermocouple”
The E.M.F. generated in a thermocouple is
called as Thermo E.M.F.
The Current which flows through the circuit is
called as Thermoelectric current.
10
Experimental set-up for Thermo EMF
+
.
-
( )
LRB
RH
HRB
Potentiometer
G
Daniel cell
THot
sand
Hot plate
TRT
Thermocouple
11
Experimental procedure
1. Primary circuit is used to calculate per unit length
resistance of potentiometer
2. Potentiometer is used to measure the thermo EMF
developed .
3. Temperature is varied using hot plate and thermo EMF is
measured as a function of thermal gradient.
12
Applications
1. Thermocouple is used as temperature measurement
device in high temperature furnaces.
2. Seeback coefficient can tell the type of carriers (electron
or hole) present in the material.
3. Carrier concentration of a semiconductor can also be
estimated.
13
References: Y. C. Bhatt
14