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3. • Thermal energy or heat flows from a place of higher temperature to a
place of lower temperature
• The 3 ways in which heat may be transferred are:
• Conduction
• Convection
• radiation

4. Conduction
• Conduction is the process whereby heat is transmitted through a
medium from one particle to another without any flow of the
material medium.
• There are 2 methods whereby conduction can take place, namely:
• Collisions between neighbouring particles, and
• Flow of free electrons (for heat conductors only)
• Therefore, conductors are able to transmit heat faster as both
mechanisms above take place at the same time, whereas insulators
can transmit heat only through collisions between particles.

5. Conduction

6. Conduction: Flow of free electrons
• Electrons near heat source gain energy and move faster.
• Free electrons can move between the particles and collide with other
electrons, allowing the less energetic electrons to gain energy and move
faster.
• This process continues to spread the heat to cooler parts.

7. Conduction in solids/liquids/gas
• In liquids and especially gases, particles are relatively far apart and
collisions between them are less frequent despite their more vigorous
vibrations of larger amplitudes
• Hence, the conduction of heat through liquids and gases is very much
slower as compared to that of solids

8. Convection
• Convection is the process whereby where heat is transmitted from
one place to another by the movement of heated particles of a gas or
liquid.
• It is the main mode of heat transfer in fluids.
• The main mechanism of convection is the change in density of liquids.

9. Convection: mechanism of action
• Fluid nearer to heat source gains heat and expands.
• Expansion causes decrease in density for the fluid nearer to heat source, causing it to
rise.
• The hotter fluid rises over the cooler fluid while the cooler fluid rushes in to take the
space.
• The process continues and a convection current is formed.
• Convection is faster than conduction as there is bulk movement (all the molecules
get hot and move up, thus it is faster than conduction.
• To form a convection current
• Heating elements are usually placed at the bottom to heat the air so as to make it
rise make the cool air sinks for it to be heated.
• Cooling elements are placed at the top to allow the air cooled by the element to sink
and allow the warm air to move up and be cooled.

10. Convection

11. Sea breeze and land breeze
• Sea breezes and
Land breezes are
also caused by
convection
currents.

12. Radiation
• Radiation is a method of heat transfer whereby the source of heat
transmits energy in the form of electromagnetic waves without the
aid of a medium.
• Radiation acts in all directions.
• An object that is a good emitter of radiation is also a good absorber of
radiation.

13. Radiation – factors affecting rate
• There are several factors which affect the emission or absorption of
radiation of an object:
• Temperature of the object: The higher the temperature the more radiation it
emits.
• Surface of the object: Dark and Dull surfaces tend to be good radiators of
radiation.
• Surface area of the object: Objects with a larger surface area will emit
infrared radiation at a higher rate.

14. Common applications of convection
• Electric Kettles:
• The heating coil is placed at the bottom of the kettle to aid transfer of thermal
energy in water by convection.
• Household hot water systems
• Air conditioners:
• It is installed near the ceiling of a room to facilitate setting up of convection
currents.
• As cool air is denser, it sinks and the warm air is drawn into the air – con where it
is cooled.

15. Radiation

16. Conduction
Describe thermal
conduction in all
solids in terms of
atomic or
molecular lattice
vibrations and
also in
terms of the
movement of free
(delocalised)
electrons in
metallic
conductors.
https://www.youtu
be.com/watch?v=
Eizsm5V8c_c
Convection
https://www.schoolphysics.co.uk/age11-
14/Heat%20energy/Transfer%20of%20heat
%20energy/text/Convection_/index.html
https://www.stevespanglerscience.com/lab/ex
periments/colorful-convection-currents/
investigate some real-life
applications of convection
currents:
1. sea and land breezes,
2. a house’s hot water
system,
3. fires used in tin mines to
ventilate the shafts,
4. hot air balloons, etc.
Radiation
https://www.bbc.co.uk/bite
size/guides/zttrd2p/revisio
n/3
Heat Transfer

17. Describe the features of a thermos
flask how they stop heat transfer
through:
1. Conduction.
2. Convection.
3. Radiation.

18. H.W
Research the methods used to insulate homes:
cavity wall insulation,
double glazed windows,
loft insulation, etc.