what are the various type to transfer heat?
from Class 7th questions CBSE
Answers
Required Answer:-
There are different modes of Heats
- Convection
- Conduction
- Radiation
Convection:-
Convection is a mode of transfer of heat in fluids( Liquid and Gas ). It take place due to actual movement of the heated particles within the material. It cannot take place in solids as the particles of solids cannot move out of their places.
Conduction:-
Conduction can take place only when
- there is a temperature difference between two bodies
- the bodies at different temperature are in direct contact.
Radiation:-
Radiation is the mode of transfer of heat from a hot body to a cold body directly, without any contact or medium between them.
The radiation carrying heat energy is called Thermal Radiation.
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Ques: What is Heat?
Ans: Heat is a form of energy which can flow from a body at higher temperature to another at lower temperature.
Answer:
Heat can travel shift from one place to another in several ways. The different modes of heat transfer include:
- Conduction
- Convection
- Radiation
Meanwhile, if the temperature difference exists between the two systems, heat will find a way to transfer from the higher to the lower system.
Convention,Conduction, Radiation
what is conduction ?
Conduction is defined as
The process in which heat flows from objects with higher temperature to objects with lower temperature.
An area of higher kinetic energy transfers thermal energy towards the lower kinetic energy area. High-speed particles clash with particles moving at a slow speed, as a result, slow speed particles increase their kinetic energy. This is a typical form of heat transfer and takes place through physical contact. Conduction is also known as thermal conduction or heat conduction.
Conduction Equation
The coefficient of thermal conductivity shows that a metal body conducts heat better when it comes to conduction. The rate of conduction can be calculated by the following equation:
Q = [K.A.(Thot−Tcold)]d
Where,
Q is the transfer of heat per unit time
K is the thermal conductivity of the body
A is the area of heat transfer
Thot is the temperature of the hot region
Tcold is the temperature of the cold region
d is the thickness of the body
Conduction Examples
Following are the examples of conduction:
Ironing of clothes is an example of conduction where the heat is conducted from the iron to the clothes.
Heat is transferred from hands to ice cube resulting in the melting of an ice cube when held in hands.
Heat conduction through the sand at the beaches. This can be experienced during summers. Sand is a good conductor of heat.
What is Convection?
Convection is defined as
The movement of fluid molecules from higher temperature regions to lower temperature regions.
Convection Equation
As the temperature of the liquid increases, the liquid’s volume also has to increase by the same factor and this effect is known as displacement. The equation to calculate the rate of convection is as follows:
Q = hc ∙ A ∙ (Ts – Tf)
Where,
Q is the heat transferred per unit time
Hc is the coefficient of convective heat transfer
A is the area of heat transfer
Ts is the surface temperature
Tf is the fluid temperature
Convection Examples
Examples of convection include:
Boiling of water, that is molecules that are denser move at the bottom while the molecules which are less dense move upwards resulting in the circular motion of the molecules so that water gets heated.
Warm water around the equator moves towards the poles while cooler water at the poles moves towards the equator.
Blood circulation in warm-blooded animals takes place with the help of convection, thereby regulating the body temperature.
What is Radiation?
Thermal radiation is generated by the emission of electromagnetic waves. These waves carry away the energy from the emitting body. Radiation takes place through a vacuum or transparent medium which can be either solid or liquid. Thermal radiation is the result of the random motion of molecules in the matter. The movement of charged electrons and protons is responsible for the emission of electromagnetic radiation.
Radiation Equation
As temperature rises, the wavelengths in the spectra of the radiation emitted decreases and shorter wavelengths radiations are emitted. Thermal radiation can be calculated by Stefan-Boltzmann law:
P = e ∙ σ ∙ A· (Tr – Tc)4
Where,
P is the net power of radiation
A is the area of radiation
Tr is the radiator temperature
Tc is the surrounding temperature
e is emissivity and σ is Stefan’s constant
Radiation Example
Following are the examples of radiation:
Microwave radiation emitted in the oven is an example of radiation.
UV rays coming from the sun is an example of radiation.
The release of alpha particles during the decaying of Uranium-238 into Thorium-234 is an example of radiation.
Unit of Heat Transfer
SI system Joule
MKS system cal
Rate of transfer of heat
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