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Conduction and convection

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Starter Experiment
- Put wood, glass and a metal rod in the
beaker of water.
- Keep checking if you can feel the ends
sticking out get warm.
-Put the materials in order of how quickly
they heated up. With fastest first.
-CAREFUL HOT WATER!! STAND UP!
Heat transfer
Lo:
Describe how energy is
transferred by particles in
conduction and convection.
Conduction
CONDUCTION is when heat moves through a solid.
Metals are better conductors of heat than plastic or
wood.
These parts are made
of plastic or wood:
These parts are made
of metal:
16/05/2019
9.2 Conductors and insulators
Conduction of heat
Conduction is the
way in which heat
energy is
transferred in
solids.
Metals are the
best conductors of
heat.
9.2 Conductors and insulators
Good conductors
A saucepan conducts heat
from a heat source
through its base to heat
the food inside. Copper is
a very good conductor;
expensive pans often have
a copper base.
9.2 Conductors and insulators
More good conductors
The skewer through a kebab
conducts heat to its centre, cooking
it more quickly.
The soleplate of an
iron conducts
heat through
it to reach
cloth being
ironed.
9.2 Conductors and insulators
Insulators
Insulators do not conduct heat
Examples of insulators:
- paper
- wood
- air
- plastic
9.2 Conductors and insulators
Using insulators
The lagging on hot water pipes
is an insulator. It stops the
heat energy getting out which
would lead to the water cooling
down.
9.2 Conductors and insulators
Paper is an insulator
Fish and chips are
sometimes wrapped in
several sheets of paper
to keep them hot.
Conduction
In this experiment we saw that liquid
water is a poor conductor of heat. The
ice cube did not melt even though the
water above it was boiling. Q. So why
does all the water in a pan get hot?
Air is also a poor conductor of
heat. This is how many types of
house insulation and clothing
keep us warm.
16/05/2019
Copy and fill in the gaps.
Energy always travels from hot things to
cold things. One way that energy can be
transferred is by conduction. Conduction
is the transfer of energy in solids. Heat
travels from one particle to the particle
next to it. In the experiment the heat
energy is transferred along the rods by
conduction.
Cold, energy, molecule, transferred, heat,
conduction, hot, particle
Copy and fill in the gaps.
Energy always travels from hot things to
cold things. One way that energy can be
transferred is by conduction. Conduction
is the transfer of energy in solids. Heat
is transferred from one particle to the
particle next to it. In the experiment the
heat energy is transferred along the rods
by conduction.
Cold, energy, molecule, transferred, heat,
conduction, hot, particle
9.3 Convection
Convection
When an area of air or water heats up it moves
upwards.
This is convection.
Convection is the way in which heat energy is
transferred in liquids and gases.
Why does it rise?
Convection happens because liquids such as water expand
when they get hot.
The particles in the water get further apart.
heat
This means the volume of the water increases.
Why does it rise?
Although the volume of the water increases, its mass stays the
same.
This means its density is less than cold water
Convection
Things which are less dense than water bob up and float on
water, like leaves on a pond.
The same thing happens in the air – a litre of helium has less
mass than a litre of air and so helium balloons float up through
the air
The same happens to warm water or air. It rises through the
colder water or air around it.
Convection currents
When water is heated
…it expands
…becomes less dense
…and rises
Cooler denser water moves in
…and is heated in turn
…and rises
As the warm water rises
…it cools
…becomes denser
…and falls again
Using convection
The glider uses convection
currents, called thermals, to
stay in the air.
Birds, like this soaring eagle,
use convection currents to
rise and fall with very little
effort.
9.3 Using convection
Heating a room
Can you explain how the whole room is heated by convection?
9.3 Using convection
Hot water tank in a house
Where is the water hottest?
Which pipe, X or Y, brings cold
water into the tank?
Which pipe, X or Y, takes hot
water out of the tank?
9.3 Using convection
Kettles and fridges
How does convection heat all
the water in the kettle?
How does convection cool the
whole of the fridge?
Convection
Convection is all about when a gas or liquid (“fluid”)
moves and carries heat with it. When the fluid is heated
it ____________. This means that it will become less
__________ than the colder fluid around it. Because of
this the warmer fluid will try to “_______” over the colder
fluid, and this is why warm air rises. This is called a
convection ___________. This is how heat reaches us
from the ___________ in this room.
Words to use: expands, radiators, dense, heated, current, float
16/05/2019
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