Heat is a form of energy that gets transferred system to the surroundings because of temperature differences. The energy gets transferred from higher temperature to lower temperature either by conduction, convection, or radiation.
Conduction mode of heat transfer occurs in solids in which molecules are directly in contact with each other, where heat gets transferred by molecular excitement.
In convection mode of heat transfer heat by actual movement of molecules of the medium. This mode of heat transfer occurs in a fluid medium because of density and temperature gradient.
In the radiation mode of heat transfer, heat energy gets transferred through all media and vacuum. The heat energy gets transferred as electromagnetic waves. The transfer of UV rays from the Sun to the earth and space is an example of Radiation.
Hence, Radiation is the fastest mode of heat transfer because the heat gets transferred as electromagnetic waves. Radiation transfer energy in a vacuum also.
