t / C T / K – 273.15 t temperature (measured in degree Celcius)
T absolute temperature (measured in kelvin)
0 K is the lowest possible temperature attainable for any object; it is called absolute zero. At this temperature all heat has been removed from the object.
The equation that defines temperature on the Celsius scale is: temperature (measured in degree Celcius) temperature (measured in kelvin) 273.15
Thermometric Property THERMOMETRIC PROPERTY
A thermometric property is a physical property that changes measurably with temperature.
For example, length of the column of liquid; emf (electromotive force) of thermocouple; volume of a gas at constant pressure; pressure of a gas at constant volume; electrical resistance; colour.2
Demonstrations of Some
Thermometric Properties Thermometers based on each of these properties can be used to demonstrate the property itself.
Length of liquid column
When a liquid is heated, it expands (its volume increases). If the liquid is in a thin capillary tube, the length of the column of liquid increases as the liquid expands. Thus, as the temperature increases, the length of the column of liquid increases. The mercury and alcohol thermometers are based on this principle (Fig 8.2).
Bulb 35 Mercury Narrow bend –60 Alcohol Fig 8.2: Clinical and laboratory thermometers Emf of thermocouple
If two different metals are joined together to form a complete circuit and the two junctions maintained at different temperatures, a small emf appears in the circuit which causes a very small electrical current to flow around the loop (Fig 8.3). The greater the
–40 –20 0 20 40 60 80 100 °C
Average body temperature
36 37 38 39 40 41 42 43 °C
2We will deal with emf and electrical resistance in more detail in Chapters 16 and 18 respectively. 124 INVESTIGATING PHYSICS
