In winter, we generally see people standing near a fire to protect themselves from the cold.
When they stand near the fire, they get some part of heat by convection.
while some part of heat reaches them by radiation as well.
The radiation does not need any medium to travel unlike other modes of heat transfer such as conduction and convection.
Radiation is the emission or transmission of energy in the form of waves or particles through space or through a material medium.
We shall study radiation in some detail here.
It would be much better if we study by comparing it with conduction and convection.
Conduction is heat transfer by direct contact
convection is heat transfer by a movement of a fluid (liquid or gas)
Here, the conduction is taking place between the kettle and stove while convection in the liquid.
The radiation is shown to be travelling in the from of waves there is no direct contact.
Radiation of heat occurs in form of the flow of electromagnetic waves.
Thus, whenever anything burns, the heat propagation occurs because of all three modes of the heat transfer.
Heat from the sun is radiation.
For its propagation, it does not need the assistance of the particles movement.
In conduction and convection, the heat propagates because of movement of particles of the medium.
The heat transmitted through the radiation is absorbed by the objects directly without any medium and they get heated.
Solar heat falls on us, then, a part of the radiated heat is absorbed, a part is reflected while the other left gets transmitted.
When radiated heat falls on a mirror, then, most of the heat gets reflected.
But when we talk about any metal, then, most of the radiated heat gets absorbed.
while that on water, major portion of the heat gets transmitted.
So, when someone gives same amount of heat to a mirror, water and a metal, then, the metal will get more heated in comparison to others.
This is because the metal has absorbed the maximum heat.
Now, since, we have studied radiation, let's try to summarize all that we have learnt till now.
Radiation is a mode of heat transfer which does not necessarily need any medium to travel.
It can travel through vacuum as well.
Radiation of heat happens because of movement of electromagnetic waves.