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Thermal Energy
Heat transferDescribe the 3 ways that heat transfer occursDecribe the process through which heat
transfer occurs in solids (describe what happens to the particles)
Thermal conductionIn non- metals the process of thermal
conduction is slow- it takes a long time for the atoms/ molecules to pass on their heat
Non- metals are not good conductors.They are good insulators
This means that non- metals are good/ bad at transferring heat
Examples of good conductors & insulatorsComplete the following table:
Good conductors Good insulators
copper glass plastic silvergold aluminium rubber airwood gases animal fur
Thermal convectionIn which states does this process occur?
Describe the process and explain why it occurs
Explain why convection can not take place in solids
Thermal convectionDecide whether the following are true or false:Hot air rises because it is more denseThe particles are closer together in lessdense
substancesColder air sinks because it is more denseConvection happens in solids, liquids and
gasesParticles are closer together in more dense
substances
To understand how heat can be transferred by convection, the idea of density is important.
If water, oil and air are mixed up, they will settle out in order of density - which one will rise to the top?
The air is least dense and the water is the most dense – it depends on how far apart the particles are.
Thermal convection
The movement of hotter areas in a liquid can be seen using potassium permanganate as a dye:
H E A T
This cycle is called a convection current.
Explain how the convection current moves using the idea of density?
The diagrams on the left will help you.
Thermal convection
Convection currents can’t occur in solids because the particles are held in fixed positions - but can they occur in gases?
Place a candle at one side of a litre beaker.
Place a piece of card down the centre, leaving a gap of 2cm at the bottom.
Make some smoke with smouldering spills and watch the path of the smoke.
Can you explain why this happens?
Thermal convection
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?
Thermal convection
Convection currents in a pan of boiling water.
4. Radiation
Heat can move by travelling as Infra Red waves
These are electromagnetic waves, like light waves, but with a longer wavelength.
This means that infra red waves act very much like light waves:
They can travel through a vacuum
They travel at 300,000,000 m/s
They can be reflected
They can’t travel through opaque materials.
Energy : heat transfer
Paint 4 thermometer bulbs with the following colours
Black White Silver Red
Place the thermometers into very hot water for 1 minute.
Take it out of the water, start the stopwatch and read the temperature.
Take the temperature every 30 seconds and put the answers in the results table on the next page.
4. Radiation
Energy : heat transfer
Colour 0 min
0.5 min
1 min
1.5 min
2 min
2.5 min
3 min
3.5 min
4 min
Temp Change
Black
White
Silver
Red
Which colour radiated most heat?
Black
4. Radiation
Energy : heat transfer
Either :
a) Draw a bar chart of your results.
Put temperature change on the y axis and colour on the x axis.
ORb) Draw a line graph of your results.
Put temperature on the y axis and time on the x axis.
Draw 4 lines on the graph, one for each colour.
4. Radiation
Energy : heat transfer
2. Why does take-away food often come in aluminium containers?
3. Why do elephants have big ears?
4. Radiation
Energy : heat transfer
1. How does a cup of tea lose heat by conduction, convection, evaporation and radiation?
5. A cup of tea takes up to 30 minutes to go cold.
This depends on the colour and shape of the cup.
Design an investigation to find out the best shape and colour of a cup to keep tea warm for longer.
4. Radiation
Energy : heat transfer
Thermos (vacuum) flask
This means that hot liquids placed inside the bottle lose hardly any heat and stay hot for very long times.
Also, cold liquids … even ice cream … stay cold for longer as the heat cannot easily get into them.
Thermos, (or vacuum), flasks are very good at slowing heat from moving into or
out of them.
They vastly reduce how quickly heat energy moves.
Glass bottle or stainless steel (unbreakable ?)
Tight fitting insulated bottle cap (lid)
Why is it important that this is insulated?
Why is it important this is designed like this?
Why is it important that this is tight fitting ?
Silvered (bright and shiny) inside and outside
covering
with hollow container walls and no particles inside i.e. vacuum
Thermos lid/cup
Insulated placers to keep the bottle safely and firmly in place, and away from the
outside wall of the container
Why is it important this is silver in colour?
Glass bottle or stainless steel (unbreakable ?)
Tight fitting insulated bottle cap (lid)
•Insulated so that there’s hardly any heat transfer by conduction
- So no heat transfer by conduction or convection
•Tight fitting so that there’s less (almost none) heat transfer by convection
Silvered (bright and shiny) inside and outside
covering
with hollow container walls and no particles inside i.e. vacuum
Thermos lid/cup
this limits the amount of heat transfer
(absorption and emission) by radiation