Name and define the mode of transfer of heat in which heat is transferred in the absence of a medium.
Dear Student,
Mode of transfer of heat are:
1.) conduction
2.) convection
3.) radiation
1.) Conduction Heat can be conducted between two bodies which are in contact with each other; heat "flows" from one to the other.
The movement caused within a fluid by the tendency of hotter and therefore less dense material to rise, and colder, denser material to sink under the influence of gravity, which consequently results in transfer of heat.
3.) Radiation is the mode in which heat is transferred in the absence of medium.
Radiation Radiation is the simplest means of heat transfer. Heat radiation is carried not by moving atoms (as in conduction or convection) but by electromagnetic waves. Radiation is the only way that heat can move through a vacuum, and is the reason that even a closed thermos bottle (which has a vacuum between the inner and outer parts) will eventually come to the same temperature as its surroundings.
Mode of transfer of heat are:
1.) conduction
2.) convection
3.) radiation
1.) Conduction Heat can be conducted between two bodies which are in contact with each other; heat "flows" from one to the other.
- Materials which conduct heat well are called conductors of heat. Electrical conductors (such as metals) are good conductors of heat.
- Materials which do not conduct heat well are called insulators. Electrical insulators (for example, wood or glass) are usually good insulators of heat. Materials with low density, such as air or foamed plastic, are normally also good insulators unless they happen to be electrical conductors. To prevent heat from moving from one place to another, we usually place an insulator between. Once a good insulator becomes hot, however, it stays that way for a long time, because it is difficult for the material to lose heat by conduction. Think of a hot ceramic pan and a hot metal pan:
The movement caused within a fluid by the tendency of hotter and therefore less dense material to rise, and colder, denser material to sink under the influence of gravity, which consequently results in transfer of heat.
3.) Radiation is the mode in which heat is transferred in the absence of medium.
Radiation Radiation is the simplest means of heat transfer. Heat radiation is carried not by moving atoms (as in conduction or convection) but by electromagnetic waves. Radiation is the only way that heat can move through a vacuum, and is the reason that even a closed thermos bottle (which has a vacuum between the inner and outer parts) will eventually come to the same temperature as its surroundings.
Heat transfer is most efficient by convection, then by conduction; radiation is the least efficient and slowest means of heat transfer. Low efficiency of heat transfer means that vacuums make excellent insulation.
Regards