THERMOELECTRICITY NOTES
B.Sc. Physics Lecture Notes
SEEBACK EFFECT
In 1821 Seeback find that current flow in a circuit consisting of two dissimilar metals when one junction are heated
while the other junction kept cold. This were remarkable experiment because no cell are used in the circuit. He
connect a plate of bismuth between copper wires connected to a galvanometer.
He find that if one of the junctions heated while the other are kept cold, then current flow through the
galvanometer. He repeat his experiment by taking a thermocouple of Fe and Cu. If both the junctions are at 0°C
there are no deflection in the galvanometer. When one of the junctions are kept constant at 0°C i.e., at the
temperature of the melting point of ice and the other junction are heated gradually, current flow in the circuit. It
were found that current flow from copper to iron at the hot junction and iron to copper at the cold junction. The
current increase until the hot junction are at a temperature 270°C. If the heating are continued beyond the 270°C,
the current decrease and finally current are zero at 540°C.
It were discover by Cumming in 1823 that on increasing the temperature of hot junction beyond 540°C the
direction of current are reversed. It flow from iron to copper through the hot junction and copper to iron through the
cold junction. The current produced in this way without the use of a cell or a battery are known as thermo-electric
current and The EMF produced in this way are called thermo-EMF, this branch of electricity are known as thermo-
electricity. The effect are known as Seeback effect.
EXPLANATION OF SEEBACK EFFECT
The free electrons inside a material can considered to constitute an electron gas. The electron density are different
in different metals. When two such dissimilar metals are joined together, electrons moves from the metal of higher
electron density to the metal of lower density. Thus potential difference are set up at the junction which are known
as contact potential difference. When the two junctions are at the same temperature there are no flow of current in
the circuit. If one of the junctions are at higher temperature, emf are set up in the circuit which results in the flow of
current. The temperature of the junction at which maximum current flow in a circuit are known as the neutral
temperature for that couple. The neutral temperature for a given thermocouple are fixed and remain constant
whatever may be the temperature of the cold junction.
If graph are plotted between the temperature of the hot junction and the thermo-EMF, the cold junction being kept
at 0°C, the graph are parabolic curve. The thermo-EMF E vary with temperature according to E = at + bt², where a
and b are constants. The point A represent the neutral temperature. The point B are the Temperature of inversion
beyond which the direction of current are reversed. The temperature of inversion are not fixed. It are as much above
the neutral temperature as cold junction are below the neutral temperature. Suppose the temperature of the cold
junction = Tc, Neutral temperature = Tn, Temperature of inversion = Ti.
B.Sc. Physics Lecture Notes
SEEBACK EFFECT
In 1821 Seeback find that current flow in a circuit consisting of two dissimilar metals when one junction are heated
while the other junction kept cold. This were remarkable experiment because no cell are used in the circuit. He
connect a plate of bismuth between copper wires connected to a galvanometer.
He find that if one of the junctions heated while the other are kept cold, then current flow through the
galvanometer. He repeat his experiment by taking a thermocouple of Fe and Cu. If both the junctions are at 0°C
there are no deflection in the galvanometer. When one of the junctions are kept constant at 0°C i.e., at the
temperature of the melting point of ice and the other junction are heated gradually, current flow in the circuit. It
were found that current flow from copper to iron at the hot junction and iron to copper at the cold junction. The
current increase until the hot junction are at a temperature 270°C. If the heating are continued beyond the 270°C,
the current decrease and finally current are zero at 540°C.
It were discover by Cumming in 1823 that on increasing the temperature of hot junction beyond 540°C the
direction of current are reversed. It flow from iron to copper through the hot junction and copper to iron through the
cold junction. The current produced in this way without the use of a cell or a battery are known as thermo-electric
current and The EMF produced in this way are called thermo-EMF, this branch of electricity are known as thermo-
electricity. The effect are known as Seeback effect.
EXPLANATION OF SEEBACK EFFECT
The free electrons inside a material can considered to constitute an electron gas. The electron density are different
in different metals. When two such dissimilar metals are joined together, electrons moves from the metal of higher
electron density to the metal of lower density. Thus potential difference are set up at the junction which are known
as contact potential difference. When the two junctions are at the same temperature there are no flow of current in
the circuit. If one of the junctions are at higher temperature, emf are set up in the circuit which results in the flow of
current. The temperature of the junction at which maximum current flow in a circuit are known as the neutral
temperature for that couple. The neutral temperature for a given thermocouple are fixed and remain constant
whatever may be the temperature of the cold junction.
If graph are plotted between the temperature of the hot junction and the thermo-EMF, the cold junction being kept
at 0°C, the graph are parabolic curve. The thermo-EMF E vary with temperature according to E = at + bt², where a
and b are constants. The point A represent the neutral temperature. The point B are the Temperature of inversion
beyond which the direction of current are reversed. The temperature of inversion are not fixed. It are as much above
the neutral temperature as cold junction are below the neutral temperature. Suppose the temperature of the cold
junction = Tc, Neutral temperature = Tn, Temperature of inversion = Ti.
