thermal effects - do now! make a list of good and bad conductors of heat

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 of particles greater • and there is greater separation of the particles and

take up more space

• OR increased pressure causes container to get bigger

http://www.schoolphysics.co.uk/animations/Heating_a_gas/index.html

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

ConductionLearning today•Insulation•Convection •A trick

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

TemperatureTEMPERATURE 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

until the two bodies reach thermal equilibrium – the same temperature

HOT COLD


Metals are good conductors of heat

Why?


Metals are good conductors of heatThey have

free electrons that can move from atom to atom carrying

thermal energy too


Most gases are poor conductors of heat (insulators)

Why?


Gases are poor conductors of heat (insulators)

The atoms are too far apart for the vibrations to be passed easily.

© Boardworks Ltd 200618 of 32

How are the particles arranged in a solid, a liquid and a gas?

What is conduction?

solid liquid gasParticles that are very close together can transfer heat energy as they vibrate. This type of heat transfer is called conduction.

What type of solids are the best conductors?

Conduction is the method of heat transfer in solids but not liquids and gases. Why?

© Boardworks Ltd 200619 of 32

How do non-metals conduct heat?

Conduction

Can you quickly and quietly gather around Ms Cornish?

Conduction

18/04/23

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 __________).

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.

Conduction – Copy Conduction – Copy

Words – vibrations, electrons, solid, heated, better

View Animation

© Boardworks Ltd 2003

Metals are different

The outer e_______ for metal atoms drift, and are free to move.

When the metal is heated, this ‘Sea of electrons’ gain k_____ energy and transfer it throughout the metal.

Insulators, such as w___ and p____, do not have this ‘Sea of electrons’ which is why they do not conduct heat as well as metals.

lectrons

inetic

ood lastic


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.

Fair – test controlling

the variables

Do Now question 4 & 5 p

109Boiling tube

Learning today• Insulation• Convection • A trick


Insulating layers of air

Other uses of a trapped insulating layer of air are-

Clothing

Cavity wallsCeiling tiles

Fibreglass

WallpaperFur coats


Insulators

Double glazing

insulating layer of air

Double glazing keeps your house warmer because the layer of a__ between the panes of glass is a poor c_______, so it acts like an i_______, it reduces heat loss by conduction from your house.

ir

onductornsulator

Task 1. Explain how to reduce heat

loss in a house use page 109

Thermal Energy Transfer

Heat can travel by Convection

Heat can travel by Convection – Copy

A hot fluid expands, so is less dense, so rises. Cold fluid takes its place. A convection current can be formed.

Examples of Convection

Thermal energy transfer

Demos

Heat cannot travel in solids by convection.

Why?

Convection the process

1. A fluid is a liquid or gas2. When a fluid is heated it expands3. This makes it less dense than the surrounding

fluid4. The heated fluid rises because it is less dense5. Cooler fluid takes its place6. In this way a circular convection current can

be formed7. Convection currents can occur in kettles8. Convection currents also cause wind.

Keywords for Convection -copy

• Fluids – air or liquid • when heated • expands • Less dense and rises

• Dense cool air or liquid takes it place • Convection current

Heat cannot travel in solids by convection.

Why?

Convection Current

• Set light to the top of the bag and wait. • The flame will burn downwards, sending a fine

stream of ash into the air. • As the flame nears the paper the tea bag

continues burning, but by this time the upward convection current is sufficient to draw the last remnants of the bag upwards and they simply float away, leaving the paper untouched.

Task Do questions 1 to 3 page

111

Do Now Conduction question

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]

Keywords for Convection -copy

• Fluids – air or liquid • when heated • expands • Less dense and rises

• Dense cool air or liquid takes it place • Convection current

Heating fluids

What happens to the particles in a liquid or a gas when you heat them?

The particles spread out and become less dense.

This effects fluid movement.What is a fluid?A liquid or gas.

Fluid movement -copy

Cooler, more d____, fluids sink through w_____, less dense fluids.

In effect warmer liquids and gases r___ up.

Cooler liquids and gases s___.

ensearmer

ise

ink

Water movement

Hot water rises

Cooler water sinks

Convection current

Cools at the surface

Why is it windy at the seaside?

Cold air sinks

Where is the freezer

compartment put in a fridge?

Freezer compartmen

t

It is put at the top, because cool air sinks, so it cools the food on the way down.

It is warmer at the

bottom, so this warmer

air rises and a

convection current is

set up.

Convection questions

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 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.

There’s another way!

¡Uno mas!

Infrared radiation

The 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

Infrared radiation - copyInfrared radiation - copy

Heat can travel by infrared radiation (“Hot light”!)

Infrared Infrared radiation - copyradiation - copy

Infrared radiation can travel through a vacuum (and through air)

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

Emission experiment –copy and complete Four containers were filled with warm water. Which container would have the warmest water after ten minutes?

Shiny metal

Dull metal

Dull black

Shiny black

The __________ container would be the warmest after ten minutes because its shiny surface reflects heat _______ back into the container so less is lost. The ________ container would be the coolest because it is the best at _______ heat radiation.

shiny metalradiation

dull blackemitting

Absorption experiment- copy and complete

Four containers were placed equidistant from a radiative heater, which container would have the warmest water after ten minutes?

The __________ container would be the warmest after ten minutes because its surface absorbs heat _______ the best. The _________ container would be the coolest because it is the poorest at __________ heat radiation.

dull blackradiation

shiny metalabsorbing

Shiny metal

Dull metal

Dull black

Shiny black

Radiation questions – please do

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.

Infrared radiationInfrared radiation

Which would cool fastest?

100°C 100°C

Shiny!

Infrared radiationInfrared radiation

Black objects are good EMITTERS of IR radiation

100°C 100°C

Shiny!

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

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?

thermal effects - do now! make a list of good and bad conductors of heat

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