What type of heat transfer involves no contact at all?
There are 3 common mechanisms of heat transfer: conduction, convection and radiation. In conduction, heat is transferred from one part of an object to the other or between objects in direct contact with each other. An example of conduction is the heating of a tea cup when hot tea is poured into it. Convection is a form of heat transfer in which the heat is transferred by the bulk movement of fluids (liquid and gases). The heating of water on a stove or heating a room by using an electric heater are examples of convective heat transfer. In the case of convection, the objects are not in direct contact with each other, but there is a medium connecting them. Radiation is the transfer of heat by electromagnetic radiation and it does not even require a medium, let alone contact. All bodies radiate heat. The solar radiation that heats up the Earth is an excellent example of radiative heat transfer.
Thus, radiation is the mechanism of heat transfer which does not require any contact (either directly or through an intervening medium).
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