# Thermal effects - Do now! Make a list of good and bad conductors of heat.

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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 gas4 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 / 0 C[1] plots occupying at least half of grid on suitable scale start at about 50 0 C 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 until the two bodies reach thermal equilibrium – the same temperature HOT COLD

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.

© Boardworks Ltd 200618 of 32 How are the particles arranged in a solid, a liquid and a gas? What is conduction? solid liquid gas Particles 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

03/07/2015 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 __________). 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 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 oodlastic

© 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.

Fair – test controlling the variables Do Now question 4 & 5

© Boardworks Ltd 2003 Insulating layers of air Other uses of a trapped insulating layer of air are- Clothing Cavity walls Ceiling tiles Fibreglass Wallpaper Fur coats

© Boardworks Ltd 2003 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 onductor nsulator

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

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.A fluid is a liquid or gas 2.When a fluid is heated it expands 3.This makes it less dense than the surrounding fluid 4.The heated fluid rises because it is less dense 5.Cooler fluid takes its place 6.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!

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 Shiny objects reflect infrared radiation. Nottingham Forest winning the champions league in 1979

Infrared radiation Which would cool fastest? 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 Shiny!

Brain maps again!

Few words Colours Pictures

Brain map Mr Porter will put the Powerpoint on loop. Can you brain-map the information?

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