Chapter- Transfer of heat ( ICSE CLASS 8)
Effects of heat
● When a body is heated, it brings about some changes in its properties called Effects of heat
● When heat is imparted to a matter, it's molecules starts vibrating/moving faster, increasing average kinetic Energy of molecules. Rise in temperature due to increase of average K.E.
At particular temperature when no rise in temperature, heat given
used up to change the state of matter.
When body is heated , gap between molecules increase and in turn, body expands
● Effects are-1. Change in temperature
2. Change in State
3. Change in shape
● Factors affecting Change in temperature-
1. Heat imparted
2. Mass of the body
3. Nature of the material of the body
● Change of state takes place when heat is either imparted or taken away from the body at particular temperature.
1. Solid to liquid - Melting
2. Liquid to Solid - Freezing
3. Liquid to Gas - Vaporization
4. Gas to Liquid- Condensation
5. Solid to Gas - Sublimation
6. Gas to Solid - deposition
● Change in size of a body may occur due to heat . Body expands on heating.
● Thermal Expansion- Expansion in a body on heating.
Thermal Expansion
● Expansion of a substance on heating is called the Thermal Expansion.
● Types- 1. Linear Expansion ( increase in length on heating)
☆ Factors affecting linear Expansion:-
i) material of wire/rod
ii) original length
Iii) rise in temperature
2. Superficial Expansion ( increase in area on heating)
☆ Factors affecting superficial Expansion
i) material of sheet/ surface
ii) original Area
Iii) rise in temperature
3. Cubical Expansion ( increase in volume on heating)
☆Factors affecting cubical Expansion
i) nature of material
ii) original volume
Iii) rise in temperature
● Relation between coefficient of linear Expansion , coefficient of superficial Expansion and coefficient of cubical Expansion is
α = coefficient of linear expansion
β = coefficient of areal expansion
γ = coefficient of volume expansion
α = β /2= γ /3
●Liquids expand more than solids and Gases expand more than Liquids.
● Expansivity of different substances are different.
● Due to differences in Expansivity of metals, a bimetallic strip bend on heating. This property of bimetallic strips is used in thermostats.
Thermostat is a device used to control temperature by making and breaking the circuit, .used in electric iron , oven , refrigerator etc.
● Invar , an alloy of iron and nickel has negligible expansion so used in pendulum clock.
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