Measurement of Temperature

Measurement of Temperature

Temperature is the measurement of the hotness and coldness of a body. It is measured with the help of a device called thermometer. The three units in which temperature is measured are Celsius, Fahrenheit, and Kelvin. Hence, there are three different scales for measuring temperature. Every unit can be converted to another unit with the help of a conversion formula that we are going to study in this lesson.


What Is Temperature?

The definition of temperature says that it is a measure of the hotness and coldness of a body. It is not easy to give an exact definition of temperature. Based on our physiological sensations, we can express the level of temperature qualitatively with words like hot, cold, warm, etc. Temperature is simply an average measure of the kinetic energy for particles of matter, the more is their kinetic energy, the higher the temperature of the body/object.


Measurement of Temperature

Measurement of temperature describes the process of measuring the temperature of an object or a body.


Temperature Measurement: Temperature is measured with thermometers that may be calibrated to a variety of temperature scales because it is a relative measurement. For accurate measurement of temperature, scales based on reference points must be used. There are three main scales commonly used to measure the temperature:


 The Fahrenheit scale, whose symbol is (°F).

The Celsius scale, whose symbol is (°C).

The Kelvin scale, whose symbol is (K).

Each of these scales has different reference points and uses a different set of divisions based on them. The Celsius scale is generally used for most temperature measuring purposes.


Device to Measure Temperature

There are several materials whose properties change with the temperature in a repeatable and predictable manner and this forms a way for accurate temperature measurement. The glass thermometer is one of the most common devices for measuring temperature. The glass thermometer is a glass tube filled with mercury or some other liquid, in which mercury acts as the working fluid. Temperature increase causes the fluid to expand and mercury changes its property with respect to the temperature. As the temperature increases the volume of mercury also increases. So, the temperature can be determined by measuring the volume of the fluid and temperature can be read simply by observing the level of the fluid in the thermometer. Generally, we use a mercury-in-glass thermometer.



Similarly, there are a few other instruments that are used for the measurement of temperature: 


Thermocouples

Thermistors

Infrared thermometer

Resistance temperature detector (RTD)

Pyrometer

Langmuir probes (for measuring electron temperature of a plasma)


Temperature vs Heat

In thermodynamics, heat and temperature are closely related concepts with precise definitions. Heat should not be confused with temperature but they can directly be related. The following table shows how temperature and heat are different from each other.


TemperatureHeat
Temperature is the measure of the degree of hotness or coldness.Heat is the transfer of thermal energy between molecules and is measured in Joules.
Temperature describes the average kinetic energy of molecules.Heat measures how energy moves or flows.
SI unit is KelvinSI unit is Joule
The unit of Temperature: Fahrenheit ÂºF, Celsius ºC, Kelvin KThe unit of heat: Joules (J) and Calories (Cal)

The symbol of temperature is "T"

The symbol of heat is "Q" 

Temperature Scales 

Temperature scales measure the hotness and coldness of a body, The three temperature scales are Celsius, Fahrenheit, and Kelvin. According to the Kelvin scale, the freezing and the boiling point of water are 273.15K and 373.15K respectively. According to the Fahrenheit scale, the freezing and the boiling point of water are 32°F and 212°F respectively. According to the Celsius scale, the freezing and the boiling point of water are 0°C and 100°C respectively.

Temperature Scales Conversion 
Using conversion formulas, temperatures can be converted from one scale to another. In temperature conversion the value of temperature changes from one unit to another. The three main conversions of temperature are:

Between Celsius and Kelvin.
Between Fahrenheit and Kelvin.
Between Celsius and Fahrenheit.

The following table shows the conversion formulas of the different units of temperature:
Conversion of Temperature  FromFormulas
Celsius to Kelvin  K = C +273.15
Kelvin to CelciusC = K −273.15
Fahrenheit to Celsius C = (F−32)59
Celsius to FahrenheitF = C95+32
Fahrenheit to Kelvin  K = (F−32)59+273.15 
Kelvin to Fahrenheit



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