The thermometric substances and temperature scales used in the construction of various thermometers
In the aspects of physical and biological sciences, the concept of temperature plays an important role. This is because the temperature of an objects is directly related to the average kinetic energy of the atoms and molecules composting the object. The science of measurement of temperature of temperature is thermometer and the instrument used for measuring temperature is a thermometer. Our perception of hot and cold is usually a measure of how rapidly energy exchange occurs between objects. If a hot and a cold body are brought together into contact, the hotter body keeps on cooling whereas the colder body becomes hotter and hotter until both bodies attain same temperature. As hotness is a measure of energy, we can say that energy has flown from the hotter body to the colder body.
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THERMOMETRIC SUBSTANCES
In order to construct a thermometer we use a substance that has some physical property which changes continuously as the temperature changes. Such substance is known as a thermometric substance. Consequently there are five good thermometric substances which are.
- Mercury and alcohol
- All gases
- platinum
- Thermocouples
- Radiant energy
TEMPERATURE SCALE
temperature is occasionally defined as the degree of hotness or coldness of a body and is a quantity which is such that when two bodies are placed in contact, Heat flows from the body at the higher temperature to the one at the lower temperature. Therefore to measure temperature scale must be established.
Instruments for measuring ordinary temperatures are known as thermometers as those for measuring high temperatures are known as pyrometers. It has also been found that a gas will not occupy any volume at a certain temperature. This temperature is known as absolute zero temperature. The temperatures measured with absolute zero as basis are called absolute temperatures. Absolute temperature is stated in degree centigrade. The point of absolute temperature is found to occur at 273°C below the freezing point of water.
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CONSTANT VOLUME GAS THERMOMETER
constant volume gas thermometers are use for standardization purposes. These thermometers use gas as the thermometric substance. Among the main advantages of the constant volume gas thermometer over the mercury in glass thermometer includes
- Gases produce large proportionate increase of volume and pressure when heated. Thus gas thermometers are more sensitive.
- Gases can be obtained in a high state of purity, and thus the thermometers are reproducible to the same degree of accuracy no matter the place of use.
- They can be used to cover a very wide range of temperature between -270 to 1500°C.
THERMOCOUPLE THERMOMETER
The thermocouple thermometer depends upon the seeback effect, namely that when wires of two dissimilar metals are joined together end to end, and the two junctions so created are kept at different temperatures, an electromotive force is developed in the circuit. Such an arrangement is called a thermocouple. The magnitude of e.m.f developed in a thermocouple and it's direction of flow depends on the nature of the given pair of wires and also on the temperature of difference between the junctions. The dependence of the e.m.f generated in a thermocouple thermometer.
An optical pyrometer
THERMODYNAMIC TEMPERATURE SCALE
This is the standard temperature scale adopted for scientific measurements. Thermodynamic temperature is measured in Kelvin K.
The thermodynamic temperature scale uses one fixed point, the triple point of water. The triple point of water is the temperature at which melting ice, pure water and saturated water vapour coexist in equilibrium. The triple point temperature is defined as 273.16K. But on the thermodynamics scale, the ice point has a temperature of 273.15K while the steam point has 373.15K.
CONCLUSION
Temperature is a fundamental quantity in physical science. The use of a thermometer to measure temperature relies on the Zeroth law which states that if two bodies are separately in equilibrium with a third body then all the three bodies are in thermal equilibrium with each other. The science of measurement is thermometer while the instrument used for measuring temperature is a thermometer.
REFERENCES
- Temperature and thermometers
- Thermometers used to measure temperature
- wikipedia: Scale of temperature
- wikipedia: Thermometers
- Wikipedia: Temperature
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