MEASUREMENT OF TEMPERATURE

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About Course

At the end of this chapter, you should be able to:

  • Explain what temperature is
  • Describe physical properties of substances which change with temperature.
  • Measure the temperature with thermometers
  • Describe suitability of alcohol and mercury for use in liquid-in-glass thermometers.
  • Describe the relationship between the Celsius and Kelvin scales.
  • Describe the structure and use of a thermocouple thermometer.
  • Demonstrate the measurement of temperature using an appropriate thermometer.

Temperature, the measure of the average heat or thermal energy of the particles in a substance, is measured under condition of the fact that some properties of the substances making the matter change with the temperature or change in temperature. These properties are among others, density, electric resistance and expansivity.

The thermodynamic scale is the one that is used for scientific measurement of the temperature. The standard unit used to measure temperature is called kelvin (K), the temperature itself being given the letter T.

The Celsius scale is now defined by . The two fixed points on this scale are the ice point (0 0C) and the steam point (100 0C). The ice point and the triple point differ by 0.01K.

Any temperature scale depends on the particular property on which it is based. In setting up a scale of temperature we must:

  • choose a property that varies with temperature,
  • assume that it varies uniformly with temperature.

KNOWLEDGE

  • The definition of Temperature: as average kinetic energy of the particles of a substance
  • Physical properties of substances: such as density, electrical resistance etc. of substances
  • Structure of thermal couple: consisting different metals, two junctions, sensitive galvanometer
  • Appropriate use of thermometers: Liquid in glass thermometers and thermocouple
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Course Content

PHYSICAL PROPERTIES AND MEASUREMENT OF TEMPERATURE
o Temperature is a measure of the average kinetic energy of the particles that make up a substance. o The properties such as density, resistance, expansivity, etc. usually vary with temperature of substances. o Temperature is measured by using different types of thermometer. o In order to measure the temperature, the thermometers use different properties of substances which change with the change in temperature. o Among the liquids used in thermometers, mercury is judged to be the most adequate for its high sensitivity to change in temperature, its colour, its high boiling and low freezing points as compared to other liquids. o Among the liquids, mercury is most preferred because its properties such as colour, conductivity, expansivity, freezing and boiling points, etc. are more suitable for measuring the temperature. o A clinical thermometer is most suitable for measuring the body temperature because of its suitable range of temperature (32˚C to 43˚C) and the constriction allowing it to take reading even after it has been removed from the source of temperature. o A thermopile and thermocouple are privileged of liquid-in-glass thermometer for their special features as far as measuring temperature is concerned: (i) They can measure a very wide range of temperatures from about - 200˚C to 1500˚C; (ii) They can measure rapidly changing temperatures; (iii) They have long leads and can therefore measure very hot places at a distance.

  • PHYSICAL PROPERTIES AND MEASUREMENT OF TEMPERATURE
    00:00
  • LIQUID-IN-GLASS THERMOMETERS and other types
    00:00

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