Transmission of Heat (Methods of Transmission of Heat)- Conduction, Convection, and Radiation Meaning

Transmission of Heat: The transfer of heat from one place to another is called the transmission of heat. It has three methods - conduction, convection, and radiation.

(1) Conduction - When the heated particles of matter give their heat to their adjacent particles without changing the place and the whole object becomes hot. This method of transmission of heat is called conduction 

In this method, the medium is required for the transmission of heat, but the medium's heated particles do not move. Molecules of solids are not free to move from one place to another, hence the transmission of heat in solids is done by this method.

Transmission of heat to liquids and gases is greatly reduced by conduction. Transmission of heat to solids and mercury is by conduction only. The transmission of heat by conduction in the matter is called 'Thermal Conductivity'.

Heat conductivity depends on the nature of the substance and the higher the conductivity of the substances, the higher the heat conductivity.

Depending on the conductivity of heat, we can classify substances in three ways.

(i) Conductor - The materials through which heat conducts easily. The heat conductivity of such substances is high. All metals, acidic water, human body, etc. are good conductors of heat.

(ii) Bad conductor - The substances which do not conduct heat easily or have very little is called kuchalak.

Wood, glass, air, gases, silica, textiles, wool, rubber, etc. are bad conductors of heat. Bad conductors are good insulators. Good insulating properties of cloth, wool, etc. are due to the air trapped between their fibers.

(iii) Thermal Insulator - The substances which do not conduct heat at all are called insulators. Eg - Ebonite, Asbestos, etc.

Transmission of Heat - Conduction, Convection, and Radiation Meaning
Transmission of Heat - Conduction, Convection, and Radiation Meaning

2. Convection - Conduction of heat in gases and liquids is done by convection method. Transmission of heat by Convection is not possible in solids. 

In this method, the particles of liquid and gas take heat from the hot part and lightly lift themselves and go towards the cold part. To replace them, particles come down from the cold part again. Thus, the heat flow in the convection method is caused by convection currents due to changes in the density of the medium from bottom to top.

Note: Earth's atmosphere is heated by the convection method.

3. Radiation - In this method, the medium is not required for the transmission of heat. It transmits heat to the vacuum. 

In this method, heat is transmitted in a straight line from the hot object to the cold object without the help of any medium and the speed of light without heating the medium. In radiation, heat moves in the form of waves called electromagnetic waves.

For example, the heat of the sun reaches the Earth by radiation method.

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