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