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Designing a conduction experiment
Can you design an experiment to investigate how well
different materials conduct heat? Remember to make your
experiment a fair test to ensure you get reliable results.
The available apparatus includes:
wax blobs tripod
metal, glass and
ceramic rods
thumb tacks
Bunsen burner
stopwatch
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Investigating conduction
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Conduction in metals and nonmetals
If you touch a piece of wood and a piece of copper metal
that are both at room temperature (about 21 °C), which
material feels warmer?
The wood feels
warmer because it is
a poor conductor.
The wood cannot conduct heat away from your hand as
quickly as the copper, which is a good conductor.
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Conduction in nonmetals
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Conduction in metals
Metals are good conductors
of heat because:
metals contain many free
electrons
the free electrons can
move between atoms at
high speed
the free electrons carry
energy from high-energy
atoms to low-energy
atoms further away from
the heat source.
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Conduction in metals
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Conduction in liquids
Metals are good conductors of heat and almost all
nonmetals are poor conductors of heat.
Are liquids good at conducting heat?
Use some gauze to hold an ice cube
at the bottom of a tube of water.
Carefully heat the water at
the top of the tube only
until this water is boiling.
If the liquid is good at
conducting, the ice should
quickly melt – it doesn’t.
Liquids are poor conductors of heat (i.e. good insulators).
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Conduction in gases
Are gases good at conducting heat?
Carefully hold a safety match
1 cm away from a Bunsen
burner flame. (Do not put the
match in the flame!)
If a gas is a good conductor,
the air between the flame and
the match should conduct heat
and light the match – it doesn’t.
Gases are poor conductors of heat (i.e. good insulators).
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Conductor or insulator?
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Convection and density
The density of a substance depends on how far apart its
particles are.
If water, oil and air are mixed
together, they will settle out in
order of density. Which one
will rise to the top?
The air is least dense and
rises to the top. The water is
the most dense and sinks to
the bottom.
This is important in explaining
how heat is transferred by
convection.
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Convection currents in a liquid
The movement of hotter
areas in a liquid can be
seen using potassium
permanganate as a dye.
This cycle is called a
convection current.
Can you use the concept
of density to explain how
the convection current
moves?
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How does convection in a liquid occur?
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Explaining convection
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Convection currents in a coal mine
When shaft mining was first used to mine coal, convection
currents caused by an underground fire were used to
ventilate the shafts.
Why do you think miners don’t use this method anymore?
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