There 3 modes in which heat is transferrred.They are conduction,convection, and radiation.Conduction is the process that only transfer heat when gets contact with the object and heat producer.Convection is the process in which hot air or water goes up and cold one comes down,when cold one gets hot it and goes up and hot on becomes cold and come down is known as convection.Radiation needs no medium for transfer of heat .
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- 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: which cools faster?
Convection
![](http://www.bluffton.edu/~bergerd/nsc_111/images/waterconvect.gif)
What we commonly call a "rolling boil" results from convection. Hot fluids rise through surrounding, cooler fluid because they are less dense; cooler fluids sink through warmer fluids because they are more dense. This causes circular motion of the fluid away from a source of heat. Convection in water drives ocean currents; convection in air drives weather patterns; and convection of molten rock inside the earth is thought to drive plate tectonics.
![](http://www.bluffton.edu/~bergerd/nsc_111/images/earthconvect.jpg)
Convection leads to the counterintuitive fact that good insulators (like air) can transfer heat efficiently -- as long as the air is allowed to move freely. Trapped air, as between panes of a double window, cannot transfer heat well because it cannot mix with air of a different temperature.
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.
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- MODES OF HEAT TRANSFER : There are three modes of heat transfer namely conduction, convection and radiation.
- Conduction : Conduction refers to the heat transfer that occurs across the medium. Medium can be solid or a fluid
- Convection : Convection refers to the heat transfer that will occur between a surface and a moving fluid when they are at different temperatures.
- Radiation : In radiation, in the absence of intervening medium, there is net heat transfer between two surfaces at different temperatures in the form of electromagnetic waves
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1. conduction: this mode of heat transfer usually takes place in solids because the molecules are closely packed.
2. convection: this mode of heat transfer is in gases and liquids .
3. radiation: this mode of heat transfer requires no medium . one such example is that the sun transfers heat to the earth by radiation
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1.conduction
the process by which heat or electricity is directly transmitted through the material of a substance when there is a difference of temperature or of electrical potential between adjoining regions, without movement of the material.
2.Convection
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
the emission of energy as electromagnetic waves or as moving subatomic particles, especially high-energy particles which cause ionization.
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The three basic modes of heat transfer are as follows -
1)conduction
2)convection
3)radiation
Conduction of heat: Heat conduction is a process in which heat is transferred from the hotter part to the colder part in a body without involving any actual movement of the molecules of the body. Heat transfer takes place from one molecule to another molecule as a result of the vibratory motion of the molecules. Heat transfer through the process of conduction occurs in substances which are in direct contact with each other. It generally takes place in solids.
For example: When frying vegetables in a pan. Heat transfer takes place from flame to the pan and then to the vegetables.
Based on the conductivity of heat, substances can be classified as conductors and insulators. Substances which conduct heat easily are known as conductors and those that do not conduct heat are known as insulators.
Convection of heat: In this process, heat is transferred in the liquid and gases from a region of higher temperature to a region of lower temperature. Convection heat transfer occurs partly due to the actual movement of molecules or due to the mass transfer.
For example: Heating of milk in a pan.
Radiation of heat: It is the process in which heat is transferred from one body to another body without involving the molecules or the medium. Radiation heat transfer does not depend on the medium.
For example: In a microwave the substances are heated directly without any heating medium.
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Conduction:It is the process of the transfer of heat energy from one particle of the solid to another without any actual movement of the particle
Convection:It Is the process of transfer of heat in liquids with the movement of molecules from one part of the fluid to another
Radiation:It is the transfer of heat energy from a hot body to a cold body without heating the space between and which does not require any medium
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No 1 conduction
No 2 convection
No 3 radiation
Conduction. the heat transfer by the adjacent particle to the another is known as conduction
Convection. The heat transfer by liquid or gas by the moment of liquid or gas is known as convection
Radiation. The heat transfer do not use any type of medium is known as radiation
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?1. conduction: this mode of heat transfer usually takes place in solids because the molecules are closely packed.
?2. convection: this mode of heat transfer is in gases and liquids .
?3. radiation: this mode of heat transfer requires no medium . one such example is that the sun transfers heat to the earth by radiation
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Conduction- conduction is a process through which the heat is transferred by the solid particles from the first and to another and the particles are the object that are good conductors of heat can only perform the process of conduction for example of plastic scale cannot perform the process of conduction but a metal strip can perform the process of conduction because metals are the good conductors of heat.
Radiation- there is no mode for that why the mode of heat transfer called radiation is used by the sun to reach the earth surface
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