Chapter 8!

-Thermal energy always flow from a region of higher temperature to a region of lower temperature.

-Thermal energy can be transferred by:-conduction,convection and radiation.

-When thermal equilibriumis reached between two bodies.there is no net flow of thermal energy between them.



what is conduction?

-conduction is a process of thermal energy transfer without any flow of the material medium.

• Thermal energy flows through the material of each rod without any flow of the material iself. Such a transfer of thermal energy without any movement of the material medium is called conduction.


• Different materials conduct heat at different rates.

-a poor conductor of heat is insulation.

what is a convection?

-convection is the transfer of thermal energy by means of currents in a fluid(liquid or gas)

-a convection current is the movement of fluid caused by the change in density in various parts of the fluid.

WHAT IS A radiation?

-Radiation is the continual emission ofinfrared waves fromthe surface of all bodies,transmitted without the aid of a medium.

-Absorption radiation is absorbed by all objects and surfaces.(causes a rise in temperature.)

-emission by all objects and surfaces where it causes temperature of the object themselves to fall.

-a good emitter of a radiant heat is also a good absorber of radiant heat.

Factors affecting rate of infrared radiation

colour and texture of the surface

• black surfaces are better absorbers og infrared radiation.

surface temperature

• the higher the temperature of the surface of the object relative to the surrounding temperature, the higer the rate of infrared radiation

surface area

• the object with the larger surface area will emit infrared radiation at a higher rate

applications of conduction

uses of good conductors of heat:

-cooking utensils

-soldering iron rods

-heat exchangers

insulators of heat:

-handles of appliances and utensils

-table mats

-sawdust

-wooden ladles

-woollen clothes

-fibre glass, felt and expanded polystyrene foam

common applicatons of convection

1. electric kettle- the heating coil of an electric kettle is placed at the bottom to aid transfer of thermal energy in water by convection

2. household hot water system

3. air-conditioner - the air is recirculated and the temperature of the air will eventually fall to the desired level

4. refrigerator - the convection of currents inside the refrigeration cabinet help cool the contents inside

common applications of radiation

1. teapots - shiny containers can keep cold liquids cool for a longer time than black containers

2. the greenhouse - the infrared radiation emitted by the contents in the greenhouse is different compared to the infrared radiation emitted by the sun. the infrared radiation emitted by the contents gets trapped. the amount of infrared radiation builds up over time, causing the temperature to increase

3. vacuum flask-designed to keep liquids hot by minimising heat loss through radiation,evaporation,conduction and convection.

Done! :D