Introduction to heat and temperature

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Heat :

• Heat is the form energy which gives us the sen­sa­tion of warmth.

• Heat flows from a hot body to a cold body when they are placed in ther­mal contact.

• It is mea­sured by an instru­ment called ‘Calorime­ter’.

• It can be also defined as it is the mea­sure­ment of aver­age kinetic energy of mol­e­cules of an object.

• The total amount of heat in an object depends upon the fol­low­ing factors:

              1. The total num­ber of mol­e­cules in the  object or the mass of the object

              2.  The aver­age kinetic energy of the mol­e­cules of the object.

•  SI unit : Joule (J).

•  CGS unit: calo­rie (Cal)

•  MKS unit : kilocalorie(Kcal)

• 4.2 joule = 1 Cal

• 1000 Cal = 1 Kcal

• 4200 J = 1Kcal

• 1 Calo­rie: The amount of heat required to raise the tem­per­a­ture of 1 gm water at 40 through 10 is called 1 calorie.

Tem­per­a­ture: 

• Tem­per­a­ture is the degree of hot­ness and cold­ness of an object.
• In other words, tem­per­a­ture is the ther­mal con­di­tion of a body which deter­mines flow of heat from it to another body in its contact.
• It also can be said that tem­per­a­ture is the aver­age kinetic energy of mol­e­cules.
• A device which is used for mea­sur­ing the tem­per­a­ture of a body is called ther­mome­ter. The ther­mome­ter works on the basis of prin­ci­ple that “when a body is heater, it expands and con­tracts on cooling.”
• SI unit: kelvin

Tem­per­a­ture scale:

• In gen­eral ther­mome­ters are cal­i­brated in centi­grade scale, Fahren­heit scale and Kelvin scale.

Centi­grade scale:

• The lower fixed point is  and upper fixed point is .
• The inter­val between these two fixed points is divided into 100 equal parts and each part is called one degree centigrade.

Fahren­heit scale:

• The lower fixed point is  and upper fixed point is .
• The inter­val between these two points is divided into 180 equal parts and each part is called one degree Fahrenheit.

Kelvin scale:

• The lower fixed point is 273K and the upper fixed point is 373K.
• The inter­val between these two points is divided into 100 equal divi­sions and each divi­sion is called one kelvin.

In short

Lower fixed points : 

Upper fixed points: 

Con­ver­sion of temperature

If C, F and K are the read­ings on Centi­grade, Fahren­heit and Kelvin scales, we can con­vert tem­per­a­ture from one scale to another scale using fol­low­ing relation.