Understanding Heat Transfer, Conduction, Convection and

Report
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
If a cup of hot coffee and an ice cube were left
on the table in this room what would happen
to them? Why?
The cup of coffee will cool until it reaches
room temperature. The ice cube will melt and
then the liquid will cool to room temperature.
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Heat always moves from a warmer place to a
cooler place.
Hot objects in a cooler room will cool to room
temperature.
Cold objects in a warmer room will heat up to
room temperature.
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These are:
 Conduction
 Convection
 Radiation
When you heat a metal strip at one end, the heat
travels to the other end.
As you heat the metal, the particles vibrate, these
vibrations make the adjacent particles vibrate, and so on
and so on, the vibrations are passed along the metal and
so is the heat. We call this? Conduction

Conduction is the process
of heat transfer through a
medium or material
without any movement of
the medium or material
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Metal is a conductor, wood is an insulator. The
metal conducts the heat away from your hands, the
wood does not conduct the heat away from your
hands as well as the metal, so the wood feels
warmer than the metal.
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Some materials conduct heat more rapidly
than others
Such materials are called thermal
conductors
Most metals are good thermal conductors
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Poor heat conductors are called insulators
They conduct heat much more slowly
Examples :
wood, rubber, asbestos,
plastic, glass, water and air
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Material
Thermal
conductivity
(W/mk)
Brass
106
Iron
84
Water
0.56
Wood
0.13
Air
0.024
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Which is the best
conductor?
--> Brass
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Thermal conductors:
We use metals to make
cooking utensils so that
the food inside cooks or
heats up quickly.
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
Boilers in a factory or
power station have to
rapidly convert heat to
steam.
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
Radiators have to
conduct heat from a hot
source before they can
warm the air around
them.
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Thermal insulators:
Thermal insulators are good at keeping heat out AND
keeping heat in.
Your winter scarf is a thermal insulator.
It prevents the heat from
your body from escaping
into the cold air.
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Handles of cooking utensils
Walls of buildings
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Second method of heat transfer
What happens to the particles in a liquid or a
gas when you heat them?
The particles spread out and
become less dense.
What
A liquid
isfluid
aorfluid?
gas.
This effects
movement.
Cooler, more d____,
ense fluids
sink through w_____,
armer less
dense fluids.
In effect warmer liquids and
gases r___
ise up.
Cooler liquids and gases s___.
ink
Cools at the
surface
Cooler
water sinks
Convection
current
Hot water
rises
Definition!
 Convection
is the transfer of heat
from one place to another by the
movement of currents in liquids or
gases
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As air is heated up on the road, it rises and cool air
replaces the warm air. This sets up a convection current.
Where is the
freezer
compartment
put in a fridge?
It is put at the
top, because
cool air sinks,
so it cools the
food on the
way down.
Freezer
compartment
It is warmer
at the
bottom, so
this warmer
air rises and
a convection
current is
set up.
A
C
B
Explanation:
Explanation:
A
B
Third method of heat transfer
How does heat energy get
from the Sun to the Earth?
?
There are no particles
between the Sun and the
Earth so it CANNOT
travel by conduction or
by convection.
RADIATION
Radiation travels in straight lines
True/False
Radiation can travel through a vacuum
True/False
Radiation requires particles to travel
True/False
Radiation travels at the speed of light
True/False
Four containers were filled with warm water. Which
container would have the warmest water after ten minutes?
Dull metal
Shiny metal
Shiny black
Dull black
shiny metal container would be the warmest after ten
The __________
minutes because its shiny surface reflects heat radiation
_______ back
dull black container
into the container so less is lost. The ________
emitting heat
would be the coolest because it is the best at _______
radiation.
Four containers were placed equidistant from a heater. Which
container would have the warmest water after ten minutes?
Dull metal
Shiny metal
Shiny black
Dull black
dull black container would be the warmest after ten
The __________
radiation the best.
minutes because its surface absorbs heat _______
shiny metal container would be the coolest because it is
The _________
the poorest at __________
absorbing heat radiation.
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Radiation is the transfer
of heat, in the form of
waves, from one place
to another without a
medium.
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1.
2.
3.
Nature of surface of body
Total surface area of body
Temperature difference between the
body and its surrounding
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1. Black, white or coloured
2. Rough, smooth or shiny
Which types
of surfaces
make better
radiators?
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Increase in surface
area, increases
amount of heat
radiated per second
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The greater the temperature difference, the
more heat is radiated per second
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How does heat from the Sun reach the
Earth?
Sun
Earth
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Sunlight is radiated through space to our
planet in the absence of matter.
The sun transfers heat through millions of
kilometres of space.
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White clothes
Houses painted in light colours
Black pipes on solar water heaters
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Styrofoam for food is white
Box covered with lid
Brightly polished kettle keeps the
liquid warm
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How does the design of the spacesuit help
astronaut survive in outer space?
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Which features of these buildings help keep the heat out?
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Why does hot air rise and cold air sink?
Cool air is more dense than warm air, so the
cool air ‘falls through’ the warm air.
Why are boilers placed beneath hot water
tanks in people’s homes?
Hot water rises.
So when the boiler heats the water, and the hot water
rises, the water tank is filled with hot water.
Why are houses painted white in hot countries?
White reflects heat radiation and keeps the house cooler.
Why are shiny foil blankets wrapped around marathon
runners at the end of a race?
The shiny metal reflects the heat radiation from the runner
back in, this stops the runner getting cold.
1.
Which of the following is not a
method of heat transfer?
A.
Radiation
B.
Insulation
C.
Conduction
D.
Convection
2. In which of the following are
the particles closest together?
A.
Solid
B.
Liquid
C.
Gas
D.
Fluid
3. How does heat energy reach
the Earth from the Sun?
A.
Radiation
B.
Conduction
C.
Convection
D.
Insulation
4. Which is the best surface for
reflecting heat radiation?
A.
Shiny white
B.
Dull white
C.
Shiny black
D.
Dull black
5. Which is the best surface for
absorbing heat radiation?
A.
Shiny white
B.
Dull white
C.
Shiny black
D.
Dull black

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