Energy Transfer b

7/28/2019 Energy Transfer b

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Conduction and Convection 09/07/2013Aim:

To explain the processes of conduction and convection

Starter:

Touch all of the following objects in the lab

Which is the coolest and hottest? Shirt

Stand

Bunsen Tube

Bunsen Chimney Bench

Chair Leg

Double Lesson


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Heating and Cooling insulator a material that is hard for heat energy to flow through.

conductor a material that is easy for heat energy to flow through dueto its free electrons

fluid a liquid or gas

Conduction

heat travelling by particles colliding together.

Main heat transfer mechanism in solids.

Fluids make bad conductors Convection Currents

Main heat transfer mechanism in liquids In your own words explain convection currents

In your own words explain convection currents



Radiation

Heat energy transfer by Infra Red electromagnetic waves (likevisible light)

Does not need particles and is thus the only heat transfermechanism in a vacuum


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Rod 2Rod 1

The faster the heat travels through the rod the quicker the

pins will drop.

Conductors can be compared to see which is the best.

Wax melts and tellsus that the heat hasarrived


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CopperSteel

Both steel and copper are good conductors.

What happens when copper and steel are heate

Conduction of heat

They are both metals and all metals are goodconductors.


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Copperglass

Glass will conduct heat but it is a non-metal.

Conduction of heat

What happens when copper and glass are heated?

Non-metals are poor conductors (insulators).


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Conduction


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Hot Cold

As the solid gets hotter the particles vibrate faster.These extra vibrations are passed along the rod. This ishow the heat spreads and we call this CONDUCTION

NON-METAL

Particle model for conduction



METAL

Positive ions pass the energy on by collisionMetals also have free electrons

The free electrons move throughthe metal and help conduction.

The electrons pass on energyby colliding with the ions (andother electrons)

Particle model for the best conductors





fluid a liquid or gas

Conduction



Fluids make bad conductors Convection Currents

Main heat transfer mechanism in liquids In your own words explain convection currents




Radiation





Conduction in Fluids A fluid is a liquid or a gas

Fluids do not conduct well

Demo Boiling water in your hand



Demos 2 gas jars with hot water

Convection Loop



Heating a Gas



Look at this particle model of a liquid How does the particle motion compare with solids?

How will heat spread through a liquid?



particlesbecome hot

gain kineticenergy

spread out

less dense

water rises(floats up)

particlescool down

lose kineticenergy

move closer

more densewater falls(sinks down)

Particles ina smallregion ofwater



Convection

l





fluid a liquid or gas Conduction



Fluids make bad conductors

Convection Currents

Main heat transfer mechanism in fluids In a paragraph or a set a notes explain convection currents

Radiation





Convection Currents in Kettles



Tea Bag Demo Remove all the tea leaves

Light the top of the bag

Thi k h h t ill d i th di



Heat

HeatHeat

Which way will the paddle wheels move?

Think how heat will spread in these diagrams

Heat

Heat

A



Heat

Heat Heat

Heat

Heat

clockwise anti-clockwise

Answers


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Sea Breeze


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C d i d C i


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Conduction and Convection recapAim:

To explain the processes of conduction and convection

R di ti d I l ti 09/07/2013


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Radiation and Insulation 09/07/2013Aim:

To explain the processes of radiation

To identify the main mechanisms of insulation

Starter:

How many senses do you have?

Can you feel where the sun is with your eyes closed?


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How does heat get to us from the sun?

S l f I f R d


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Some examples of Infra Red

Movie - Walking in Woodland

Man in Chair

Movie - Firemen

Heating and Cooling
http://localhost/var/www/apps/conversion/tmp/scratch_8/Energy%20-%20Transfer%20-%2004%20-%20Movie%20IR%20Clip%20Woman%20in%20Wood.mpghttp://localhost/var/www/apps/conversion/tmp/scratch_8/Energy%20-%20Transfer%20-%2004%20-%20Movie%20IR%20Clip%20Man%20in%20Chair.mpghttp://localhost/var/www/apps/conversion/tmp/scratch_8/Physics%201a%20-%20Heat%20-%2001%20-%20Movie%20IR%20Clip%20Through%20Smoke.mpghttp://localhost/var/www/apps/conversion/tmp/scratch_8/Energy%20-%20Transfer%20-%2004%20-%20Movie%20IR%20Clip%20Firemen%20Hot%20Smoke%20Rising.mpghttp://localhost/var/www/apps/conversion/tmp/scratch_8/Energy%20-%20Transfer%20-%2004%20-%20Movie%20IR%20Clip%20Firemen%20Hot%20Smoke%20Rising.mpghttp://localhost/var/www/apps/conversion/tmp/scratch_8/Energy%20-%20Transfer%20-%2004%20-%20Movie%20IR%20Clip%20Firemen%20Hot%20Smoke%20Rising.mpghttp://localhost/var/www/apps/conversion/tmp/scratch_8/Energy%20-%20Transfer%20-%2004%20-%20Movie%20IR%20Clip%20Firemen%20Hot%20Smoke%20Rising.mpghttp://localhost/var/www/apps/conversion/tmp/scratch_8/Energy%20-%20Transfer%20-%2004%20-%20Movie%20IR%20Clip%20Firemen%20Hot%20Smoke%20Rising.mpghttp://localhost/var/www/apps/conversion/tmp/scratch_8/Physics%201a%20-%20Heat%20-%2001%20-%20Movie%20IR%20Clip%20Through%20Smoke.mpghttp://localhost/var/www/apps/conversion/tmp/scratch_8/Energy%20-%20Transfer%20-%2004%20-%20Movie%20IR%20Clip%20Man%20in%20Chair.mpghttp://localhost/var/www/apps/conversion/tmp/scratch_8/Energy%20-%20Transfer%20-%2004%20-%20Movie%20IR%20Clip%20Woman%20in%20Wood.mpghttp://localhost/var/www/apps/conversion/tmp/scratch_8/Energy%20-%20Transfer%20-%2004%20-%20Movie%20IR%20Clip%20Woman%20in%20Wood.mpghttp://localhost/var/www/apps/conversion/tmp/scratch_8/Energy%20-%20Transfer%20-%2004%20-%20Movie%20IR%20Clip%20Woman%20in%20Wood.mpghttp://localhost/var/www/apps/conversion/tmp/scratch_8/Energy%20-%20Transfer%20-%2004%20-%20Movie%20IR%20Clip%20Woman%20in%20Wood.mpg


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Convection Currents

Main heat transfer mechanism in liquids


Radiation



Black matt objects absorb and emit the most infra red radiation

Shiny white objects absorb and emit the least infra red radiation

Mi i P ti l


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Mini Practical Wrap a dark piece of foil around one

hand and a light one around the other

Which hand gets hot first when heldnear to a Bunsen?

h l


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Investigating thermal absorption

h l


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Investigating thermal emission

Heating and Cooling


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Convection Currents

Main heat transfer mechanism in liquids


Radiation



Black matt objects absorb and emit the most infra red radiation

Shiny white objects absorb and emit the least infra red radiation

Infrared radiati n true r false?


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Infrared radiation true or false?

Which type of heat transfer?


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Which type of heat transfer?

Insulation


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Insulation Charlie forgot to take the chicken out of the freezer last night! Will his plan to defrost the chicken in time for lunch work?

Effective Insulators


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Effective Insulators Think about the following effective insulating materials

What do they have in common?

Why are they good insulators?

Duvet filling Expanded polystyreneHair Cotton

Insulation


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Insulation Insulation will slow down heat flow

Keep cold things cold and hot things hot

Some materials make good insulators (e.g. ceramics)

Most insulators are improved by:

trapping pockets of air

pockets are too small for convection currents air is a bad conductor

How does a vacuum flask work?


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How is a vacuum flask able to keep hot drinks hot and colddrinks cold?

How does a vacuum flask work?

2. The plastic (or cork) lid is aninsulator and the screw topprevents convectioncurrentsescaping from the flask.

1. There is a vacuum between twolayers of glass or steel, whichprevents heat leaving orentering by conduction.

3. The walls have silvery surfaces,which prevent heat leaving or

entering by radiation.


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Movie

Multiple choice quiz
http://localhost/var/www/apps/conversion/tmp/scratch_8/Energy%20-%20Transfer%20-%2004%20-%20Movie%20Energy%20Types%20and%20Transfers,%20Thermal%20Transfers%20-%20CB.avihttp://localhost/var/www/apps/conversion/tmp/scratch_8/Energy%20-%20Transfer%20-%2004%20-%20Movie%20Energy%20Types%20and%20Transfers,%20Thermal%20Transfers%20-%20CB.avi


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Multiple-choice quiz

Insulation recap


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Insulation recap

Aims

Identify that gases are poor conductors of heat. Investigate the best way to insulate a test tube of hot

water.

Insulating Homes 09/07/2013


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Insulating Homes 09/07/2013Aim To name methods of insulating housing

To state what types of heat transfer they prevent To explain how they work

Anagrams


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Anagrams

Losing Energy


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In order to reduceelectricity bills andpollution, we need tokeep energy lossesfrom our homes to a

minimum.

We lose energy from the roof, the door,

the walls and the windows.

Losing Energy

Home Insulation


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Home Insulation

As we go through the next few slides complete the table below

Dont copy the words on the slides, read and summarise

Method Heat transfermechanism prevented

How?

Curtain Convection

Radiation

Curtains


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Curtains reduce draughts [convection currents]leaving the house. They are opaque and so dontallow much radiated heat to pass through them.

Curtains

Home Insulation


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Home Insulation

As we go through the next few slides complete the table below

Dont copy the words on the slides, read and summarise

Method Heat transfermechanism prevented

How?

Curtain Convection

Radiation

They reduce draughts (convectioncurrents)

Opaque so prevent IR travelling out

Double Glazing


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A great deal of energy is lostthrough windows.

By adding an extra pane, thetrapped air in between acts as aninsulator to reduce heat loss byconduction.

The insulating effect of the gapcan be improved further bysucking all the air out to create avacuum.

Double glazing is expensive anddifficult to smash without aspecial hammer.

Double Glazing

Cavity Wall Insulation


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Most outside walls have an emptyspace between the 2 layers ofbricks called a cavity.

This reduces heat loss byconductionthrough the bricks.

Cavity wall foam insulation ispumped in between the bricks toprevent convectionwithin the

cavity.

Cavity Wall Insulation

Loft Insulation


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The air heated by centralheating is less dense than the

cooler air around it and rises.

The ceilings get heated andeventually the heat escapesthrough the roof.

Loft insulation contains trappedair which forms an insulatinglayer between the rooms andthe attic.

Loft Insulation

Radiators


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Radiators heat the wall a greatdeal - this wastes heat energy.

Placing shiny silver coated card

between the wall and theradiator reduces heat loss byradiation by reflecting it backinto the room.

Radiators

Draught Excluders


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Draughts are convection

currents.A great deal of heat energy islost in this way but it is theeasiest type to prevent.

Draught excluders are hairy orspongy strips which close gapsand prevent the convectioncurrents escaping.

Draught Excluders

Insulation and heat transfer


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Insulation and heat transfer

Insulation and heat loss true or false?


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Insulation and heat loss true or false?

Sim Energy


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Sim Energy We will be going to the computer room to play sim

energy

The program is in year 10\teachers\physics\sim energy Double click on sim energy.exe

Flat

Semi-Detatched

Detatched
http://localhost/var/www/apps/conversion/tmp/scratch_8/sim%20energy/sim_level1_flat.swfhttp://localhost/var/www/apps/conversion/tmp/scratch_8/sim%20energy/sim_level1_semi.swfhttp://localhost/var/www/apps/conversion/tmp/scratch_8/sim%20energy/sim_level1_detached.swfhttp://localhost/var/www/apps/conversion/tmp/scratch_8/sim%20energy/sim_level1_detached.swfhttp://localhost/var/www/apps/conversion/tmp/scratch_8/sim%20energy/sim_level1_semi.swfhttp://localhost/var/www/apps/conversion/tmp/scratch_8/sim%20energy/sim_level1_semi.swfhttp://localhost/var/www/apps/conversion/tmp/scratch_8/sim%20energy/sim_level1_semi.swfhttp://localhost/var/www/apps/conversion/tmp/scratch_8/sim%20energy/sim_level1_flat.swf


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Movie: Arctic Clothing

Keeping Warm recap
http://localhost/var/www/apps/conversion/tmp/scratch_8/Energy%20-%20Transfer%20-%2005%20-%20Movie%20Antartic%20Clothing%20-%20175.mpghttp://localhost/var/www/apps/conversion/tmp/scratch_8/Energy%20-%20Transfer%20-%2005%20-%20Movie%20Antartic%20Clothing%20-%20175.mpg


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Keeping Warm recapAim To name methods of insulating housing

To state what types of heat transfer they prevent To explain how they work

Plenary

Whiteboards types, methods and mechanisms

Documents

Energy Transfer b