Explanation:
A process that involves transfer of heat from a hot substance to a cold substance by coming in contact with each other is known as conduction.
For example, a person has his hands cupped around a ceramic mug of hot chocolate then heat is transferring from ceramic mug to the hands.
Whereas a process in which heat energy is transferred in a wave-like motion through the space is known as radiation.
For example, a person is toasting a marshmallow above the fire is getting heat energy in the form of radiation.
Also, third person who is roasting a hot dog above the glowing coals is getting heat energy in the form of radiation.
Hence, we can conclude that primary source of heat transfer for person 1 is conduction, and for both person 2 and 3 is radiation.
