Explanation:
Conduction, convection and radiation are the modes of heat transfer:
Conduction:
Microscopic level of heat transfer
Also called as thermal diffusion(takes place due to atomic vibrations) and is highly invisible
Primarily occurs in solid-solid systems and stagnant liquids
Convection:
Macroscopic level of heat transfer
Primary occurs in fluids(involves bulk movement of fluids)
2 types of convection are possible — with external source of energy (forced convection) and without external source of energy (free convection)
Radiation:
Transfer occurs through electromagnetic waves
No medium is required unlike conduction and convection. Radiation can occur even in vacuum.
These are different processes of transferring energy from one place to another.
Radiation is the sunlight and (heat). It travels as electromagnetic wave and does not need matter to transfer energy. Hence radiation is the only mode of transferring energy in vaccuum, for example, light of visible and invisible wavelengths reaches from the sun and other stars as electromagnetic radiaton. Human body emits heat wave as radiation.
Convection and conduction refers to energy transfer through the motion of matter. The difference is how the molecules of matter move during the energy transfer.
Convection is that mode of energy transfer when matter also transfer from one place to another during energy transfer. Molecules of liquids and gases can move. So convection occurs in liquids and gases. It is visible when water is boiled on a gas burner.
Molecules of solids are too tightly bound to move. They vibrate about some average positions in space. Conduction is that mode of energy transfer when matter on average is not transferred from one place to another. Propagation of sound through solid wall is an example.
