Thermoelectric Thermometer

Introduction to thermoelectric thermometer:

A thermometer is used to measure temperature  of a body. Temperature may be defined as a thermal condition of a body which determines its ability to transfer heat to other bodies. The thermal equilibrium of two bodies  kept in contact for a ling time can be tested by a third body which is a device used to measure temperature. Such a device is called thermometer. A device which measures the thermal condition of a body i scaled thermometer.

Thermometers are classified depending upon the physical property of substance  used  in them such as Liquid thermometers , Gas thermometers, Resistance thermometers , Thermoelectric thermometers, Radiation thermometers, Va pour pressure thermometers.

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Thermoelectric thermometer


When the junctions of two dissimilar metals are maintained at different temperatures an emf is generated. This effect is called thermoelectric effect or Seebeck effect. The pair of metals used to generate the emf  is referred to as a thermocouple. The emf causes a current in the circuit as shown by the deflection produced in a galvanometer  introduced in the circuit as shown in the figure below.

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The emf increases with the temperature difference between teh hot and cold junctions of a thermocouple. It reaches a maximum value at a certain temperature of thehot junction called neutral temperature.

Thermoelectric thermometer is based on the thermoelectric effect. Keeping the cold junction in melting ice and heating the hot junction to different temperatures determined by a constant volume hydrogen thermometer, the emf at each temperature is measured. A calibration curve is drawn plotting emf against temperature. Then the temperature of any body can be found from the graph by measuring the emf, keeping the body in contact with the hot junction.

Thermocouples are used to measure temperatures in the range of -250^0 C to 3000^0 C.