Thermal electromotive force (EMF) is generated when dissimilar metals touch, creating a small voltage. The thermoelectric effect directly converts temperature differences into voltage and vice versa. Specifically, the Seebeck effect produces a voltage when two different conductors or semiconductors have a temperature difference at their junction, proportional to the temperature difference. This physical principle is used in thermocouples for temperature measurement. The Peltier effect involves heating or cooling at the junction of two conductors when an electric current passes through.

1. Prepared by
Md. Kabir Ahamed
Student of
Department of Applied Physics & Electronics
Bangabandhu Sheikh Mujibur Rahman Science &
Technology University, Gopalganj – 8100

3. What is Thermal Electromotive Force (EMF)?
Reference: http://www.pidtechinsights.com/2012/03/13/thermal-electromotive-force-emf/
Thermal electromotive force (EMF) is generated when the
dissimilar metals that make up terminals, contact springs and
contacts touch. This electromotive force, measured in micro
volts, could be very small or large and can create undesirable
noise during electrical measurements.
What do you understand by thermoelectric effect?
The thermoelectric effect is the direct conversion of
temperature differences to electric voltage and vice-versa.

5. The Seebeck effect is a phenomenon in which a temperature
difference between two dissimilar electrical conductors or
semiconductors produces a voltage difference between the two
substances.
Reference: http://www.pidtechinsights.com/2012/03/13/thermal-electromotive-force-emf/
In 1821 German physicist Thomas
Johann Seebeck discovered that a
compass needle would be
deflected by a closed loop formed
by two metals joined in two
places, with a temperature
difference between the junctions.
This was because the metals
responded differently to the
temperature difference, creating a
current loop and a magnetic field.

6. Reference: http://searchnetworking.techtarget.com/definition/Seebeck-effect/
The voltage produced is proportional to the temperature difference
between the two junctions. The proportionality constant (a) is known
as the Seebeck coefficient, and often referred to as the thermoelectric
power or thermopower.
The Seebeck voltage does not depend on the distribution of
temperature along the metals between the junctions. This is the
physical basis for a thermocouple, which is used often for temperature
measurement.
E = a (Th - Tc)
Here,
E = Generated EMF
a = Seebeck Constant
Th = Temperature on hot junction
Tc = Temperature on cold junction

7. Reference: http://searchnetworking.techtarget.com/definition/Seebeck-effect/
The voltages produced by Seebeck effect are small, usually only a few
microvolts (millionths of a volt) per kelvin of temperature difference at
the junction. If the temperature difference is large enough, some
Seebeck-effect devices can produce a few millivolts. Numerous such
devices can be connected in series to increase the output voltage or in
parallel to increase the maximum deliverable current. Large arrays of
Seebeck-effect devices can provide useful, small-scale electrical power
if a large temperature difference is maintained across the junctions.
In 2008, physicists discovered what they are calling the spin Seebeck
effect. The spin Seebeck effect is seen when heat is applied to a
magnetized metal. As a result, electrons rearrange themselves
according to their spin. Unlike ordinary electron movement, this
rearrangement does not create heat as a waste product. The spin
Seebeck effect could lead to the development of smaller, faster and
more energy-efficient microchips as well as spintronics devices.

9. The Peltier effect is the presence of heating or cooling at an
electrified junction of two different conductors.
Reference: http://en.wikipedia.org/wiki/Thermoelectric_effect/

10. When a current is made to flow through a junction between two
conductors A and B, heat may be generated (or removed) at the
junction. The Peltier heat generated at the junction per unit
time, Q is equal to,
Reference: http://en.wikipedia.org/wiki/Thermoelectric_effect/
where ПA and ПB is the Peltier coefficient of conductor A and B
respectively, and I is the electric current (from A to B).
The Peltier coefficients represent how much heat is carried per
unit charge. Since charge current must be continuous across a
junction, the associated heat flow will develop a discontinuity if
ПA and ПB are different.
Q = (ПA – ПB) I