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.
1.  What Is Temperature? 
2.  Measurement of Temperature 
3.  Device to Measure Temperature 
4.  Temperature vs Heat 
5.  Temperature Scales 
6.  Temperature Scales Conversion 
7.  FAQs on Temperature 
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 mercuryinglass 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.
Temperature  Heat 

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 Kelvin  SI unit is Joule 
The unit of Temperature: Fahrenheit ^{º}F, Celsius ºC, Kelvin K  The 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 From  Formulas 

Celsius to Kelvin  \( \text{ K = C }+ 273.15\) 
Kelvin to Celcius  \( \text {C = K }− 273.15\) 
Fahrenheit to Celsius  \( \text {C = (F}  32) \dfrac59 \) 
Celsius to Fahrenheit  \( \text {F = C} \dfrac95 + 32 \) 
Fahrenheit to Kelvin  \(\text{ K = (F}  32) \dfrac59 + 273.15\) 
Kelvin to Fahrenheit  \( \text {F = (K}  273.15 ) \dfrac95 +32 \) 
Important Notes:
 Temperature is simply an average measure of the kinetic energy for particles of matter.
 The Celsius scale is generally used for most temperature measuring purposes.
 The Fahrenheit (°F) temperature scale is used in the United States.
Solved Examples on Temperature

Example 1: Noah knows that onedegree Celsius is equal to 273.15 Kelvin. He wants to calculate 30°C in Kelvin. How much is 30°C in Kelvin?
Solution: Given, Onedegree Celsius is equal to 273.15 Kelvin. From the temperature conversion formula, we can convert Celsius to Kelvin that is, K = C + 273.15. Putting the value: K = 30 + 273.15K = 303.15 K.
Therefore, 30°C in Kelvin is 303.15 K 
Example 2: Isabella knows the body temperature is generally 37ºC. Now she wants to know the body temperature in Fahrenheit. Can you help her?
Solution:Given, the body temperature on the Celcius scale is 37ºC. Using the formula of conversion from Celsius to Fahrenheit is \( \text {F = (C}× \dfrac95) + 32 \)
Substituting the value, we get \(\text F=37^\circ \text C \times \dfrac {9}{5} + 32 \text F = 98.6\)
Therefore, the body temperature in Fahrenheit is 98.6F. 
Example 3: Joseph knows that the freezing point of water on the kelvin scale is 273.15K. He wants to know the freezing point of water on the Fahrenheit scale. Can you help him find the answer?
Solution: Given, the freezing point of water on the Kelvin scale is 273.15K. We know that \(\text{F = (K}  273.15 )\dfrac{9}{5}+32\). So, by substituting the value of K, the freezing point of water on the Fahrenheit scale is 32°F.
Practice Questions on Temperature
FAQs on Temperature
What does Temperature Measure?
Temperature measures the hotness and coldness of a body. In other words, when we measure the temperature of an object, we actually measure the average kinetic energy of all the particles in the object.
What is Temperature?
Temperature is a physical quantity that expresses the hotness and coldness of a body in Celsius, Fahrenheit or Kelvin scale.
Which Temperature Scales have no Negative Values?
Kelvin scale has no negative values and the lowest value that it shows is 0.
Which Temperature Scale is the Most Commonly Used?
Fahrenheit is most commonly used temperature scale.
Which Temperature Scale is Most Commonly Used for Scientific Researches?
Kelvin scale is most commonly used for scientific researches.