Temperature Scales - JEE Important Topic

In our daily life, we use the term temperature to define how hot or cold an object is, temperature is actually the measure of the average kinetic energy of particles in a matter. In chemistry, the temperature is considered a very important parameter as it affects the rate of chemical reactions. Temperature is also the reason behind the physical changes like changes in the state of matter. A solid changes to a liquid when the temperature is increased. In this topic, we’ll learn about the different types of temperature measurement methods and types of temperature scales used.

Different Scales of Temperature

The temperature scale is a parameter for measuring temperature. Temperature is mainly measured using four different scales.

• Kelvin Scale: The Kelvin scale was invented by a British physicist, William Thompson, popularly known as Lord Kelvin. The kinetic theory of molecular motion is the basis of the kelvin scale. It is also known as the absolute scale of temperature. Absolute zero is the temperature at which no molecular motion occurs on the Kelvin scale, and is considered the coldest possible temperature. On the Kelvin scale, the freezing point of water is 273K, and the boiling point of water is 373K. There are no negative values on this scale. The Kelvin scale is used in scientific calculations and the SI unit of temperature is kelvin represented by K.

• Celsius Scale: This scale was created by Swedish astronomer Anders Celsius. It is abbreviated by the symbol ${}^{\circ}C$. This is a common unit of temperature. The freezing point of water on the Celsius scale is taken as ${0}^{\circ}C$and the boiling point is taken as ${100}^{\circ}C$. 

• Fahrenheit Scale: This scale was invented by a German physicist, Daniel Gabriel Fahrenheit. The symbol of the Fahrenheit Scale is ${}^{\circ}F$. On the Fahrenheit Scale, the freezing point of water is ${32}^{\circ}F$and the boiling point is ${212}^{\circ}F$. This scale is used in the United States. 

• Reaumur Scale: This scale was introduced by Rene-Antoine Ferchault de Reaumur. On this scale, zero represents the freezing point of water and 80 represents the boiling point. 

Relationship Between Different Scales

• The relationship between Kelvin and Celsius scales is given by C = K - 273.

• Here, C is the temperature in Celsius and K is the temperature in Kelvin.

• The relationship between Fahrenheit and Kelvin scale is given by 

• $F=\dfrac{9}{5}(K-273)+32$

• Here, F is the temperature in Fahrenheit and K is the temperature in Kelvin

• The relationship between Celsius and Fahrenheit scale is given by $F=\left(\dfrac{9}{5}\times C\right)+32$

Here,  F is the temperature in Fahrenheit and C is the temperature in Celsius.

Devices to Measure Temperature

The device widely used for the measurement of temperature is the thermometer.  The mercury thermometer was first invented by Gabriel Fahrenheit in 1974, which consisted of a long narrow glass tube with scales marked on it to measure the temperature. At one end of the glass tube, there is a small bulb containing mercury in it. The glass tube contains a capillary where mercury expands whenever the thermometer comes in contact with a hot object. There are two types of mercury thermometers:

• Clinical Thermometer: They are used in homes, clinics, and hospitals to measure the human body temperature. Thermometer scales include both the Celsius scale and the Fahrenheit scales marked on the two sides of the glass tube. They can measure temperature from ${35}^{\circ}C$ or ${94}^{\circ}F$ to ${42}^{\circ}C$ or ${108}^{\circ}F$.

• Laboratory Thermometer: These thermometers are used in laboratories to measure boiling points, melting points and other temperatures. The thermometer scale used here is celsius. They can measure temperature ranging from $-{10}^{\circ}C$ to $-{110}^{\circ}C$.

• Digital Thermometer: Digital thermometer displays the temperature numerically on a digital screen. They are a good alternative to mercury thermometers as they don’t use mercury, which is hard to dispose of.

• Infrared Thermometer: Infrared thermometer is a thermometer which measures temperature from a portion of the thermal radiation emitted by the object being measured.

Other than thermometers, thermocouples, thermistors, RTD’s are some other devices that are used to measure temperature.

Conclusion

There are four different types of scales used in measuring temperature. These include the Kelvin scale, Celsius Scale, Fahrenheit Scale and Reaumur Scale. All these scales have different symbols and different values of boiling and freezing point of water. The temperature of one scale can be converted into the temperature of another scale by using the relationships between different scales. Different devices have been invented to measure temperature, but the most used device is the thermometer, which can further be of many types such as: clinical thermometer, laboratory thermometer, digital thermometer and infrared thermometer.