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Construction of Thermoelectric Thermometer
Posted Date:
15 Aug 2007
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Posted By: Jose Mathew
Member Level: Platinum Posted Date: 15 Aug 2007
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TOPIC : CONSTRUCTION OF THERMO ELECTRIC THERMOMETER
INTRODUCTION
Thermoelectircy refers to phenomena that occur at junctions of dissimilar conductors or within a single conductor. When a temperature difference exists between the junctions or across a conductor.
In 1821, Thomson Johann Seebeck, a German Physicist, discovered that a current flowed in an electric circuit made of two different conductors, when the two junctions in the circuit were kept at different temperatures. A magnetic compass needle held close to such a circuit showed deflection due to the magnetic field produced by the current. This meant current flowing through the conductors. The two junction circuit is called thermocouple. The thermoelectric current rather small, generally of the order of µa is used to measure current. The effect is reversible. If the hot and cold junctions are interchanged, the direction of current reverses.
THEORY
When two dissimilar metals joined together ends. And one junction of the thermocouple is kept at any fixed temperature (cold) and the other junction is kept in the region of heating, an e.m.f is developed between the two junctions. This is due to the flow of current. This current is called thermo electric current.
APPARATUS
Copper wire, constant wire, thermometer, two beakers and a micro ammeter, coconut oil, ice cubes, spirit lamp.
PROCEDURE
Copper and constant wires are joined to form a thermocouple. W connected the wires that should not be touch except at their ends. One of the junction of a thermocouple is kept cold as zero degree. To this, we took a beaker with ice inside it and dipped one junction to it. The other junction is kept as hot. To this we took oil in beaker and boiled it by the spirit lamp. And a thermometer dipped in this oil to measure the temperature and the other junction (hot) is dipped in this oil.
Picture -1
The reading of micro ammeter is noted that connected to the junction at the centre of the copper wire and the temperature of the hot junction is also noted.
Then a graph is plotted with temperature along x axis and thermo electric current along y axis.
OBSERVATIONS
(I) The direction of current
Hot junction is T1, & Cold junction is T2, then the direction of current is (in copper –constantan)
Picture-2
(ii) The variation of current with increasing temperature, when temperature of the cold junction is 24oc.
Table-1
(iii) the gauge of the copper wire. – 0.3 mm
the gauge of the constantan wire – 0.3 mm
RESULT
? The current is produced due to the difference between cold and hot junction.
? The producing current depends upon the Nature of the metals forming thermocouple.
? The thermo electric current is directly proportional to the temperature of the hot junction.
? When the area of cross section is high the producing electricity is higher.
? When the length increases the producing thermo electricity is decreases.
? The direction of current depends upon the type of metals forming thermo couple.
REFERENCE
? Plus two PHYSICS – XAVIER & Joy – Rosary Publications – 2006
? NCERT TEXT – Plus two PHYSICS.
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