how can we say that heat from the sun reach the earth by radiation and not by conduction and convection
Answers
The sun's light and heat cannot reach us by conduction or convection because space is almost completely empty. There is nothing to transfer the energy from the sun to the earth. When the sunlight hits the earth, some of its radiation is absorbed and some is reflected.
in Conduction and convection , Particles of the medium is required.
These particles transfer heat from one place to another...
For example , In conduction , When a body gets heated , the Particles of the body only oscilate about its mean position and pass this oscillation to its neighbouring particle.
By doing so , Particles do not move place to place for the transfer of heat and heat is then transferred...
In convection , particle of the medium is must as in this process , particle of the medium , move one place to other and carry enery ( heat )
But , there is no particles or medium between the Earth and Sun...We call it space or Vacuum...But still heat reaches to Earth...So this is obvious that there is one more process rather than Conduction and Convection...Which is nothing just called Radiation...
In radiation to transfer the heat...no medium is required...Hope this help...