Measurement of temperature

2.2.1 Thermal expansion of solids, liquids and gases

2.2.3 Thermal capacity

Measurement of temperature

  1. Concepts

    1. A physical property that varies with temperature may be used to measure temperature, e.g. thermal expansion
    2. Sensitivity is the smallest temperature change that can be detected
    3. Range is the range of temperature that can be measured
    4. Linearity is the uniformity of change
    5. Fixed points are needed to calibrate thermometers, such as the melting & boiling point of water

  2. Application

    1. A liquid-in-glass thermometer consists of a liquid, generally mercury or alcohol, in a bulb & stem where the liquid can expand and contract; a temperature scale can be fixed on the stem after calibration using fixed points, such as splitting the distance between the melting point of water at 0 °C and the boiling point of water at 100 °C into 100 equal gradations
    2. A thermocouple consists of two dissimilar metallic wires that are coupled at the probe tip and extended to the reference junction, such as in an ice bath; a difference of temperature produces a voltage that can be used to calculate the temperature difference between the junctions and thus the measured temperature
    3. Thermocouples have a large range, fast responsivity and high sensitivity