Transcript Lesson 9 Thermal Expansion Conduction..

Thermal effects - Do now!
• Make a list of
good and bad
conductors of
heat
Learning today
• Thermal expansion of solids, liquids
and gases
• Conduction of heat energy.
• Conduction experiments
• Insulation
Thermal expansion
• When a material is heated, its volume
will increase slightly
• Why?
• Demos
Thermal energy transfer
Can you quickly and quietly gather
around Ms Cornish?
Thermal expansion- Copy
• When a material is heated, its volume will increase
slightly, Why?
• The kinetic theory explains thermal
expansion as follows:
• As the particles are heated they gain
kinetic energy and vibrate more.
• The particles take up more space so
the material will expand.
• Important the particles size remains
the same it is the space between them
that increases.
Task - Thermal Expansion
• Explain in terms of molecules, how
thermal expansion takes place in a
solid and in a gas
4 marks
• Do question 1 & 2 page 105
Thermal Expansion
• Explain in terms of molecules, how thermal
expansion takes place in a solid and in a gas 4 marks
• SOLID higher temperature means greater KE for the
particles
• particles vibrate more and take up more space.
• GAS KE of particles greater
• and there is greater separation of the particles and
take up more space
• OR increased pressure causes container to get bigger
Graphs
Graphs
top
marks
Graph
• y-axis labelled θ / 0C
[1]
• plots occupying at least half of grid on
suitable scale
start at about 50 0C on the y - axis
[1]
• all plots correct to ½ square
[1]
• well judged single, smooth curve line,
not ‘point-to-point’
[1]
• thin line
[1]
Graph Mark scheme
Conduction
Heat can travel by
Conduction
Hot particles vibrate more, so collide
with adjacent particles. The heat
energy travels from hot to cooler
areas.
hot
cold
Temperature
TEMPERATURE is measure of internal
energy that determines the direction of flow of
thermal (heat ) energy between two bodies in
thermal contact
Heat flows from where its hot
to where its not
HOT
COLD
until the two bodies reach thermal
Heat can travel by
Conduction
Metals are good conductors of heat
Why
?
Heat can travel by
Conduction
Metals are good conductors of heat
They have
free electrons
that can move
from atom to
atom carrying
thermal
energy too
Heat can travel by
Conduction
Most gases are poor conductors of heat
(insulators)
Why
?
Heat can travel by
Conduction
Gases are poor conductors of heat
(insulators)
The atoms are
too far apart for
the vibrations to
be passed easily.
What is conduction?
How are the particles arranged in a solid, a liquid and a gas?
solid
liquid
gas
Particles that are very close together can transfer heat
energy as they vibrate. This type of heat transfer is called
conduction.
Conduction is the method of heat transfer in solids but
not liquids and gases. Why?
What type of solids are the best conductors?
18 of 32
© Boardworks Ltd 2006
How do non-metals conduct heat?
19 of 32
© Boardworks Ltd 2006
Conduction
Can you quickly and quietly gather
around Ms Cornish?
Conduction
Conduction – Copy
09/04/2015
Conduction is all about when heat is transferred through a
_________. The heat is passed on by ___________ in the
molecules. These vibrations get LARGER when the solid has
more ENERGY (i.e. when it is being __________).
View Animation
Metals are _______ conductors than non-metals. This is
because the heat is carried by free ________ that can
carry the energy around the metal and give it to other
electrons and ions.
Metals are the best conductors, non–metals and liquids are
poor conductors and gases are the worst.
Words – vibrations, electrons, solid, heated, better
Metals are different
The outer e_______
lectrons for metal
atoms drift, and are free to move.
When the metal is
heated, this ‘Sea of
inetic
electrons’ gain k_____
energy and transfer it
throughout the metal.
Insulators, such as w___
ood and p____,
lastic do not
have this ‘Sea of electrons’ which is why they
do not conduct heat as well as metals.
© Boardworks Ltd 2003
Why does metal feel colder than wood, if they
are both at the same temperature?
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.
© Boardworks Ltd 2003
Do Now
question
4&5
Fair – test
controlling
the variables
Insulating layers of air
Other uses of a trapped insulating layer of air are-
Clothing
Ceiling tiles
Cavity walls
Fibreglass
Fur coats
Wallpaper
© Boardworks Ltd 2003
Insulators
insulating layer of air
Double glazing keeps your
house warmer because the
ir between the
layer of a__
panes of glass is a poor
onductor so it acts like an
c_______,
i_______,
nsulator it reduces heat loss
by conduction from your house.
Double glazing
© Boardworks Ltd 2003
Task
1. Explain how
to reduce heat
loss in a house
use page 109
Mark scheme
• 5 (a) (i) conduction
1
• (ii) particles vibrate OR electrons move
and carry energy
1
• pass on energy from one particle to the
next
1
[3 Marks]
Thermal Energy Transfer
Heat can travel by
Convection
Heat can travel by
Convection
A hot fluid expands, so is less dense, so
rises. Cold fluid takes its place. A
convection current can be formed.
Examples of Convection
Heat cannot travel in solids
by convection.
Why
?
Thermal energy transfer
Can you quickly and quietly gather
around Ms Cornish?
Draw the sentence
1.
2.
3.
4.
5.
6.
A fluid is a liquid or gas
When a fluid is heated it expands
This makes it less dense than the surrounding fluid
The heated fluid rises because it is less dense
Cooler fluid takes its place
In this way a circular convection current can be
formed
7. Convection currents can occur in kettles
8. Convection currents also cause wind.
Task
Do questions
1 to 3 page
111
There’s another way!
¡Uno mas!
Infrared radiation
Infrared radiation
Heat can travel by infrared radiation
(“Hot light”!)
Infrared radiation
Infrared radiation can travel through a
vacuum (and through air)
An experiment!
Can you gather
again around Mr
Porter?
Infrared radiation
Black objects are good absorbers of
infrared radiation.
Infrared radiation
Shiny objects reflect infrared
radiation.
Nottingham
Forest winning
the champions
league in 1979
Infrared radiation
Which would cool fastest?
100°C
100°C
Shiny!
Let’s try!
1. Carefully fill two cans with boiling
water.
2. Take their temperature every 5
minutes, filling in the table Mr Porter
has just given you.
Whilst you’re doing that you can do a
brain map of the previous pages!
Infrared radiation
Black objects are good EMITTERS of IR
radiation
100°C
100°C
Shiny!
Brain maps again!
Brain maps again!
• Few words
• Colours
• Pictures
Brain map
Mr Porter will put the Powerpoint on
loop. Can you brain-map the
information?