Sunday, 18 January 2015


Firstly , when a temperature difference occurs between two bodies or a body with its surroundings , heat transfer occurs.
There are basically three modes of heat transfer :--

(1.) Conduction  :-- Conduction is mode of                                      heat transfer in which heat                                is transferred via direct                                             contact.

For e.g  :-- If we touch a hot plate or pot , we are going to feel the heat because we are touching it , its because of direct contact and is due to conduction.

Conduction generally occurs in solids and liquids.

In conduction heat is transferred due to the vibrations and collisions between the medium particles which occurs due to the source of heat.

(2.) Convection  :-- Convection is the transfer                               of heat due to the actual                                   movement of the medium                                 particles.

Convection generally occurs in fluids ( liquids and gases ).

For e.g :-- When a liquid is heated it expands                  and this lowers its density.

The less dense liquid rises and its place is taken by more dense colder liquid.
This movement of liquid is responsible for the heat transfer and this is the basic principle behind convection.

(3.) Radiation  :-- Radiation is the transfer of                               heat via indirect contact or                               not touching.

It is basically heat travelling through air or space.
It is also described as the flow of heat from one place to another by means of electromagnetic waves.
It is very common because it is the primary method of heat transfer like in case of fire and sun.

For e.g :-- If we sit near fire we feel warmth , it is due to radiation.

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