MODULE mod7A mod7B mod7C mod7D mod7E mod7F mod7G mod7H mod7I mod7J mod7K mod7L mod8A mod8B mod8C mod8D mod8E mod8F mod8G mod8H mod8I mod8J mod8K mod8L mod9A mod9B mod9C mod9D mod9E mod9F mod9G mod9H mod9I mod9J mod9K mod9L 8ia1
8Ia1 Heat energy and temperature 1
Name _____________________________ Class ____________
Which volume of water gets hot quicker?
Heat energy and temperature are not the same.
You are going to heat two different volumes of water to find out which volume of water gets hot quicker. You will give them the same amount of heat energy by heating them for the same length of time.
Prediction
I think the ______________________ (biggest/smallest) volume of water will get hot quicker.
Apparatus
- Water - Heatproof mat
- Beaker - Bunsen burner
- Thermometer - Measuring cylinder
- Tripod - Stopclock
- Gauze - Eye protection
thermometer
gauze
heatproof mat
tripod beaker
water
Label the diagram using the words in the box.
Method
1 Measure 100 cm3 of water and pour it into the beaker.
2 Measure the temperature of the water, and write it in the table.
3 Light the Bunsen burner.
4 Put the beaker on the gauze and start the stopclock.
5 Write down the temperature every two minutes until the water has been heated for 10 minutes.
6 Repeat steps 1 to 5, but this time use 200 cm3 of water.
Wear eye protection.
Recording your results
Time (mins)
Temperature of 100 cm3 water (ºC)
Temperature of 200 cm3 water (ºC)
0
2
4
6
8
10
Considering your results/conclusions
The temperature of the water in the first beaker went up by _____________________ °C.
The temperature of the water in the second beaker went up by _____________________ °C.
Both beakers were given the same amount of heat energy. The temperature went up the most in the
beaker with _____________________ (100 cm3/200 cm3) of water in it.
The beaker which had the water with the highest temperature was beaker ____________________ .
Both beakers were given the same amount of _____________________ energy but the water with
the _____________________ volume had the highest temperature.
Thermometers measure how _____________________ things are, not how much heat energy is
in them.
[ observing, considering ]
8Ia2 Heat energy and temperature 2
Heat energy and temperature are not the same thing. You are going to investigate what happens when different volumes of water are given the same amount of heat energy.
1 Make a prediction. Which volume of water do you think will get the hottest?
ear eye protection.
Heat 100 cm3 of water for 10 minutes, and measure its temperature every 2 minutes. Then repeat the experiment using 200 cm3 of water.
Planning
2 Describe how you will carry out your investigation. Use the information above to help you.
3 Draw a labelled diagram to show your apparatus.
4 How are you going to make sure that both beakers get the same amount of heat energy?
5 Draw a table ready for your results, then carry out your experiment.
6 Draw a line graph to show how the temperature of the water changed. Time should be on the horizontal axis.
7 Which volume of water reached the highest temperature? Was your prediction correct?
[ planning, observing, presenting, considering ]
8Ia3 Temperature survey
Plan a survey to find out which temperatures people know.
1 Who will you ask?
2 How will you ask the questions?
3 What questions will you ask? The results table below will help you.
4 How many people do you need to ask? Explain why you have chosen this number of people.
5 How will you record their ages? You could use age ranges such as: 12-13, 14-15, 16-19, 20 or over
6 Where will you find out the correct answers?
7 How are you going to present your results? You could use a table like the one below.
8 How will you summarise the results?
Person 1
Person 2
Person 3
Person 4
Person 5
Person 6
Person 7
Name
Age range
Different temperatures
Guess °C
Actual °C
Boiling water
Melting ice
Room temperature
Hottest temperature reached on Earth
Hot oven
Safe fridge temperature
Safe freezer temperature
Considering your results/conclusion
9 Will you draw a graph of your results or use a spreadsheet?
10 Which age group was the most accurate? Why do you think this was so?
8Ia4 Temperature versus heat
The temperature of something tells us how hot it is in degrees Celsius (°C). It does not tell us how much heat energy is in it.
The water in both beakers is at the same temperature but the water in the large beaker has 5 times as much heat energy in it.
1 Fill in the gaps in the sentences using words from the box below. You can use each word once, more than once, or not at all.
The amount of heat _____________________ in an object depends on
_____________________ things: its temperature, its mass, and the _____________________
it is made from.
A tank full of hot water at 60 °C contains _____________________ heat energy than a cup
full of water at the same temperature because there is _____________________ water in it.
A cup full of water at 50 °C contains _____________________ heat energy than the same
mass of water at 100 °C because the water is at a _____________________ temperature.
energy higher less lower material more same three
2 Look at the diagrams below and tick the one of each pair that has the most heat energy in it. In each case, explain your answer.
q q
a large bowl of porridge at 30 °C small bowl of porridge at 30 °C
______________________________________________________________________
b small pan of soup at 80 °C the same size pan of soup at 50 °C
c a small mug of coffee at 80 °C a large mug of coffee at 80 °C
d a pot full of tea at 85 °C the same amount of tea at 95 °C
3 a What units are used to measure heat energy? __________________________________
b What units are used for temperature? _______________________________________
c What instrument do we use for measuring temperature? _________________________
_____________________________________________________________________
[ knowledge ]
8Ia5 Thermometers
You need to use a thermometer or a temperature sensor if you want to measure temperature. The table shows some of the different types of thermometers and temperature sensors available today.
Thermometer
Mercury in glass
Range: -39 °C to 630 °C
Advantages: accurate, mercury expands easily and is easy to see.
Disadvantages: expensive, dangerous if broken (mercury is poisonous).
Alcohol in glass
Range: -117 °C to 79 °C
Advantages: cheap, can be used in very cold areas.
Disadvantages: may not be accurate (alcohol sticks to the glass).
Sensor
Thermistor
This is a resistor and the resistance varies with temperature. It is used as part of an electric circuit.
Range: depends on the type of thermistor used.
Advantages: can give continuous readings, provides an electrical signal which can be used by computer equipment.
Disadvantages: may have limited range, not very accurate.
Thermocouple
Two metals joined in a circuit can generate a small voltage when there is a difference in temperature between the two ends.
Range: depends on metals used.
Advantages: cheap, gives continuous readings, can measure the temperature of very small objects.
Disadvantages: not always very accurate.
Liquid crystal
Some crystals change colour when their temperature changes.
Range: depends on the types of liquid crystals used.
Advantage: cheap, easy to read.
Disadvantages: not very accurate.
Different thermometers and sensors measure different temperature ranges. If you need to measure the temperature, you need to choose the right thermometer or sensor for the job.
1 Many school science departments used to use mercury in glass thermometers, but now use alcohol in glass instead. Write down two reasons why you think they changed.
2 An expedition to the Antarctic needs to choose a thermometer to take with them. Which kind of thermometer would you recommend? Explain your answer.
3 If you feel ill, your parents or a doctor may take your temperature. Which kind of thermometer do you think your parents would use? Explain your answer.
4 Liquid crystals can be made into flexible strips that can be held against someone's forehead. Why do you think these thermometers are often used to take the temperature of young babies.
5 Which kind of sensor could be used to control the temperature inside a fridge? Explain your answer.
8Ia6 How much energy?
It is easy to measure how hot something is by using a thermometer. It is much more difficult to measure how much heat energy is in something. However, we can measure how much energy is put into something. The amount of energy it takes to heat up 1 kg of a substance by 1°C is called the specific heat capacity of a substance.
This experiment was set up to find out how much heat energy is needed to heat up different materials.
A 50 watt heater is placed into some liquids and metals. The heater transfers 50 J of energy every second.
How liquids are heated. How metals are heated.
1 What is the variable which is being changed in the investigation above?
2 a Write down the variables which must be kept the same to keep it a fair test. (You should be able to write down at least three.)
b How can these variables be kept the same?
One kilogram of each substance was heated for 10 minutes and the temperature change recorded in the table below.
Substance
Temperature change after 10 mins (°C)
7
brine (salt water)
paraffin
13
aluminium
33
iron
60
copper
75
3 If 2 kg of each substance were heated, what do you think the temperature changes would be? The results in the table can be used to calculate the specific heat capacities of the different materials.
4 a How much energy is transferred by the heater in 10 minutes?
b Calculate the specific heat capacities of the materials above. To do this divide the energy transferred by the temperature rise.
5 The values you calculated will not be exactly the same as the specific heat capacities given in text books. Suggest why your values might be different, and how the experiment could be made more accurate.
[ knowledge, numeracy ]
8Ib1Good conductors? 1
Materials which let heat travel along them are good conductors. Some materials are better conductors than others.
- Bunsen burner - Copper rod
- Glass rod - Iron rod
- Heatproof mat - Tripod
- Wrap-around - Wire
temperature sensor - Datalogger
- Stopclock
The rods will get very hot. Let them cool down before you touch them.
1 Read the instructions here and then fill in your prediction on the next page.
2 Fasten one of the rods to the tripod using a piece of wire.
3 Set up the rest of the apparatus as shown in the diagram.
4 Light the Bunsen burner.
5 Stand the Bunsen burner under the end of the rod and start the stopclock. Stop it when the temperature at the other end of the rod has gone up by 5 °C. Write the time in the table on the next page.
6 Repeat steps 2 to 5 for the other materials. Make sure the temperature probe is the same distance from the Bunsen burner flame each time.
Fill in the gaps using words from the box. You may not need to use all of the words. You may need to use some words more than once.
When I heat the end of a rod the ___________________ will travel along the rod by conduction.
The temperature of the rod will increase. I think the ___________________ at the end of the rod
made of ___________________ will go up the fastest, because ___________________ is a metal,
and ___________________ are good heat conductors.
copper glass heat iron metals temperature
Material
glass
Draw a bar chart to show your results.
Fill in the gaps in the sentences using words from the box. You may not need to use all of the words, and you may need to use some words more than once.
I have made this a fair test by having the temperature probe the same distance from the heated end of the rod each time.
The temperature at the end of the ___________________ rod went up the fastest. This means that
heat travels fastest along ___________________ , so this is the best ___________________ .
The temperature of the ___________________ took longest to rise. This means that heat energy
travelled along this rod the slowest, so this is the worst ___________________ . It is an
___________________ .
conductor copper glass insulator iron metals
[ observing, presenting, considering ]
8Ib2 Good conductors? 2
Which materials are good conductors?
Materials that let heat travel along them are good conductors. Some materials
are better conductors than others. You are going to find out which material is the
best conductor.
- Rods of different materials - Tripod
- Bunsen burner - Beaker
- Heatproof mat - Wire
- Wrap-around - Hot water
1 Which rod do you think will be the best conductor? Explain why you think so.
2 How can you test the materials to see which is the best conductor? The diagram above suggests one method, but this method may not be suitable for all materials.
3 Write a method for your investigation. Remember to say how you will make sure it is a fair test.
4 Draw a table for your results.
5 Show your plan to your teacher before you start.
6 Record your results in your table. Draw a bar chart to show your results.
7 Write a list of the materials you tested in order, with the best conductor first.
8 Was your prediction correct?
Evaluation
9 Is there any way you could improve this investigation if you did it again?
[ planning, observing, presenting, considering, evaluating ]
8Ib3 Heat flow
A material that allows vibrations to be passed on easily from particle to particle is a good conductor of heat. A poor conductor is also called an insulator. Metals are good conductors. Glass, air, wood and plastic are poor conductors and therefore are good insulators.
Complete the table below.
Item
What it is made of
How it helps or prevents heat flow
Conductor or insulator?
kettle element
(heater)
steel
Allows heat to flow to the water.
conductor
kettle handle
plastic
pot
pottery
Stops heat flowing out of the food inside.
base of the iron
ironing board
wood and
cover
padded fabric
wok
metal (steel or aluminium)
stirrer
wood
table mats
cork
8Ib4 Heat and insulation
Look carefully at the picture.
1 Colour metal objects in green.
2 Colour all the insulators yellow.
3 Colour all the hot things in red.
4 Complete the table below for five more of the insulators in the picture.
Insulator
Does it use trapped air?
8Ib5 Conducting heat
A material which allows heat energy to pass on easily from particle to particle is a good conductor of heat. A poor conductor is called an insulator. Glass, air, wood and plastic are poor conductors.
1 These drawing pins are stuck to a metal rod with wax. Which pin will fall off first? Explain your answer in terms of the particle model of matter.
2 Good conductors allow heat to be transferred quickly, so if you touch them they feel cold.
a Which window frame will feel colder when you touch it?
b Is the glass a conductor or insulator?
c Double glazing has an air gap between two sheets of glass. Why is double glazing better than single glazing at stopping heat escaping?
3 Some Inuit people live in igloos made of ice. Why does the igloo stay warm inside?
4 What is the advantage of putting the potatoes on the metal spikes while cooking them?
5 Explain why the water is boiling at the top of this tube but the ice has not melted.
6 Look in your kitchen at home and make a list of five conductors and five insulators. Put them in a table like this:
8Ib6 Cold feet
The person on the left is wearing insulated boots, so the heat from his body is not transferred to the snow he is standing on.
The person on the right is well wrapped up, apart from his feet. He has cold feet, but why is the rest of his body cold?
The penguins are well insulated with a layer of fat and feathers, but they do not have any insulation on their feet, so why aren't the penguins cold?
1 a Human body temperature is usually 37 °C. What will be the temperature of the blood at point A?
b What will happen to the heat energy in the blood as it flows through the blood vessels at B?
c How will the temperature of the blood at C compare with the temperature of the blood at A?
d What will happen to the temperature of the blood as it flows back into the body?
e How will this affect the temperature of the rest of the body?
2 What do you notice about the arrangement of the blood vessels in humans and in penguins?
3 Copy the diagram of the penguin's foot. On your copy, show where the blood will be warm and cold, and explain how the arrangement of blood vessels helps to keep the penguin warm.
Emperor penguins live a long way from the sea. When a pair have mated and the female has laid an egg, the male bird looks after the egg while the female travels to the sea to feed. He keeps the egg warm by holding it on his feet, under a flap of skin.
4 How is the egg insulated from:
a the cold air
b the snow?
5 How do the blood vessels in the flap of skin help to keep the egg warm?
6 If your body cools down too much, you can suffer from hypothermia. Find out what the symptoms of hypothermia are, and how to treat someone with hypothermia.
[ knowledge, literacy, research ]
8Ic1 Making a thermometer
How can you make your own thermometer?
- Conical flask - Large bowl
- Beaker - Crushed ice
- Water - Water bath set to 50°C
- Thin bore glass tubing fitted in a bung - Coloured dye
- Ruler - Eye protection - Marker pens
Be very careful with the glass tubing. It can break easily.
1 Fill a bowl with crushed ice.
2 Put a little coloured dye in the flask, then fill it to the top with cold water. Stand it in the bowl of crushed ice and leave it for 15 minutes.
3 Carefully push the rubber bung into the top of the flask. You should see the coloured water in the glass tube. Mark the level of the water in the tube.
4 Put the flask into a water bath, and leave it for 15 minutes.
5 Mark the new level of the water in the glass tube.
6 Divide the distance between your two marks into 5 equal divisions.
7 Leave your flask on the bench for 15 minutes (or until the next lesson). Mark the new level of the water.
1 a What temperature does the bottom mark on your tube represent?
b What temperature does the top mark represent?
c How many degrees does each division represent?
2 What was the room temperature you measured using your thermometer?
3 Why did you only mark ten-degree divisions?
4 How could you work out how much the water rises for each degree?
5 Why is this not a very accurate thermometer?
6 How could you change the thermometer to make it faster to use?
8Ic2 Explaining convection
A purple chemical can be used to show convection currents. The jumbled up sentences below explain how convection currents form. Cut out the statements below, and stick them into your book in the correct order.
[ knowledge, literacy ]
---------------------------------------------------------------------------------------------------------
The purple crystal starts to dissolve and colours the water purple.
The rising water transfers some heat energy to the cooler water around it. Eventually it becomes the same temperature as the water around it, which is now a little warmer than it was to start with.
When the particles take up more space, the water is less dense than the water around it, and it starts to rise. You can see this happening because some of the purple dye is carried upwards with the water.
Eventually the convection current will spread heat energy (and the purple dye!) through all the water in the beaker.
The cool water warms up and starts to rise. A convection current has formed.
The water particles that are being heated start to move faster. They take up more space.
The beaker is heated underneath the purple crystal.
Heat energy is conducted through the glass of the beaker and starts to heat the water.
A purple crystal is dropped into the water.
Cooler water moves in to take the place of the warm water. More of the purple crystal dissolves.
8Ic3 The heat goes on 1
Complete the sentences using the words in the box. You may need some words more than once.
When a liquid is heated the _______________________ part of the liquid rises.
Cooler liquid _______________________ in to replace it. This creates a flow
which is called a _______________________ current. Convection happens in
_______________________ as well as in liquids. A hot drink is
_______________________ by convection currents. Bubble wrap has lots of
pockets of trapped _______________________ . Heat does not travel through
air by _______________________ very well. Because the air is
air
conduction
convection
cooled
gases
hottermoves
radiation
reflect space
trapped
warm
_____________________ , heat is not lost by _____________________ either.
The energy from the Sun travels to the Earth by _______________________ .
Radiation can travel through transparent things and through
_______________________ .
Shiny materials _______________________ radiation. Foil can be used to help
keep the body _______________________ .
8Ic4 Conduction and convection
1 For each statement decide if it is true or false.
If it is true write it in your book.
If it is not true write a correct version in your book.
a A fluid is a gas or a liquid.
b Convection can take place in all fluids.
c Convection cannot take place in a solid because the particles can only vibrate and not move from one place to another.
d Heat energy travels through space (a vacuum) by convection.
e Heat energy travels through solids by conduction.
f A liquid will sink when it is hotter than the liquid around it.
g Conduction cannot take place in a liquid.
h Air, water and steam are all fluids.
i Heat energy travels through gases by convection.
j When air loses its heat it becomes less dense and sinks.
2 a Which food will be the coldest in this fridge?
b Explain your answer.
3 a Which cake will bake faster in this oven?
b Explain your answer
[ literacy, knowledge ]
8Ic5 The heat goes on 2
1 Why can't the Sun's heat reach us by conduction or convection?
2 Explain how a radiator warms the room by convection. Use a diagram to help you to explain.
3 Bubble wrap contains trapped gas. How does this help to insulate something wrapped in it?
4 Which items in the pictures below work by conduction and which by convection? Write a sentence for each one. The first one has been done for you.
a b
c d
e f
8Ic6 Using convection
Heating causes particles to gain more kinetic energy and move around at higher speeds. The fluid expands and its volume becomes greater. The mass of material in the fluid does not change, so it becomes less dense. In a mixture of hot and cold fluids the cold, denser fluid sinks and the hot, less dense fluid rises. This creates convection currents.
The diagram shows how water is heated in many homes.
1 Write out these sentences in order, so that they explain how your taps are supplied with hot water.
A The water expands so its volume becomes bigger.
B Cooler water flows in to replace it.
C The header tank provides the pressure to push the hot water to the taps.
D Water is heated in the boiler.
E Heating causes the particles to gain more kinetic energy and move around at higher speeds.
F The cooler water is heated.
G After a time, a supply of hot water collects in the storage tank. The water in the tank becomes hot from the top down.
H This means that the warm water becomes less dense and rises to the storage tank.
2 Why is there an expansion pipe at the top?
3 Insulators are used to prevent heat loss or to hold heat in for a long time. Storage heaters in the home contain bricks, which take a while to heat up.
a Heat from inside the bricks reaches the surface of the bricks very slowly once the heat is switched off. Why does it take a long time?
b How is the air around the bricks warmed up?
c Explain how this system heats up a room.
4 Hot water tanks often have two heating elements in them.
a Which heating element would you switch on to heat the whole tank? Explain your answer.
b What is the advantage of having the other heating element in place? (Hint: Think about how much it costs to heat the whole tank of water.)
5 Why do you think the ice box in a fridge is at the top?
8Ic7 Convection currents
Convection currents occur when hot air rises and cold air sinks. Hot air rises because it expands when heated and becomes less dense. This means that the same mass of air takes up more volume. As the warm air rises and meets cooler air it cools down and because of this it becomes denser. If it becomes more dense than the surrounding air it will start to sink. The same process takes place in liquids.
Convection currents can also start with air being cooled. In this case the cold air is more dense than the air surrounding it, and it sinks.
1 Why are the cooling pipes at the top of the fridge? How is the rest of the air in the fridge cooled? Explain in as much detail as you can.
2 How does the food in the fridge cool down?
3 The pipes behind the fridge are warm. Where has the energy come from to warm these pipes?
4 How does the heat get away from the back of the fridge?
Sean poured out two hot cups of coffee. Carla put a saucer on top of hers, but Sean did not. They had a discussion about whether or not the cover made a difference to how long the coffee stayed hot. They decided to carry out an investigation. These are their results.
Time in minutes
Covered coffee temperature (°C)
90
82
74
67
61
56
Uncovered coffee temperature (°C)
77
65
54
44
38
5 Plot a graph of their results. Put time along the horizontal axis.
6 What is the difference in temperature between the two cups of coffee after 5 minutes?
7 Approximately how long does it take each cup to cool to 50 °C?
8 How does the cover prevent heat escaping? (There are two ways.)
[ knowledge, presenting, considering ]
8Id1 Testing insulation 1
Which is the best material for insulating the walls of a house?
Insulators are materials that do not let heat go through them. Many insulators rely on trapped air.
Label this diagram using words from the apparatus list.
- Large beaker
- Small beaker
- Thermometer
- Hot water
- Insulating materials
- Cling film
Fill in the gaps using words from the apparatus list.
I will put a small beaker inside a large ____________________ .
I will put some ___________________ ___________________ into the gap between the beakers.
I will fill the small beaker with ___________________ ___________________ and put a
___________________into it.
I will cover the top of the beaker with cling film.
I will write down the temperature and start the ___________________ .
I will write down the temperature every 2 minutes for 20 minutes.
I will repeat the experiment with different ___________________ ___________________ .
Material 1 was ___________________
Material 2 was ___________________
Material 3 was ___________________
Temperature (ºC)
Material 1
Material 2
Material 3
12
14
16
18
20
Temperature change
I have found out that the best insulating material is ___________________ .
This is because the temperature of the water only went down by ___________________ when I
used this material. This was less of a decrease than with the other materials.
Is there any way you could have made your investigation better?
_______________________________________________________________________________
[ observing, considering, evaluation ]
8Id2 Testing insulation 2
Insulators are materials that do not let heat go through them. Many insulators rely on trapped air. You can investigate which materials would make the best insulators.
- Large beakers
- Small beakers
- Thermometers
1 Draw a labelled diagram to show how you will use your apparatus.
2 Describe how you will carry out your investigation.
- How many materials will you test?
- Which materials will you test?
- How often will you measure the temperature?
- How long will your investigation last?
3 How will you make it a fair test?
4 Record your results in a neat table.
5 Plot a line graph to show your results.
6 Which was the best insulator? How do you know?
7 Could you improve your experiment if you had time to do it again? Explain how.
8 How could you use the apparatus to find out if double glazing is a good insulator?
8Id3 Saving energy 1
Some of the answers to these questions are shown jumbled up in brackets at the end of the question.
1 Materials which do not allow heat to go through them are called ______________________ . (latorssinu)
2 Bubble wrap is a good insulator because it contains _________________________________ . (artdepp ria)
3 Put a circle around the insulating methods used that contain trapped air.
4 Insulating our homes saves burning ______________________ . (flossi flues)
5 It important to use less fossil fuels because they are non- ______________________ . (ablenewre)
6 Put the following words into the correct column in the table:
bubble wrap metal taps
copper pipes duck feathers
brass door handles
wool carpet wooden door
Conductor
8Id4 Saving energy 2
1 Explain why bubble wrap is a good insulator. Use ideas about particles in your explanation.
2 Why will insulating our homes save burning fossil fuels?
3 Why is it important to use less fossil fuels?
4 Copy the table below, and put the following words into the correct column:
bubble wrap metal opper pipes duck feathers
brass door handles wool carpet wooden door
5 a Write down all the insulating methods used in the house below that use trapped air.
b Write down the insulating methods that stop air moving.
8Id5 Hot homes
Most of us like to live in a warm home. A lot of heat energy escapes through the walls, roof, etc. We need to reduce the heat loss, because it saves money and cuts down on the amount of fossil fuels used.
The table below compares houses with and without insulation. The first column shows how much of the total heat energy lost in an uninsulated house is lost through the walls, windows, etc. The second column shows how much energy is lost when different kinds of insulation are fitted, compared to the total energy loss for the uninsulated house.
NO INSULATION
INSULATION
cavity wall 30%
cavity wall filling 15%
single glazing 15%
double glazing 8%
floor 15%
carpet on floor 10%
door 15%
door with draught excluder 8%
loft 25%
loft and insulation 12%
wall
windows
floor
door
loft
Total
30%
15%
25%
100%
1 Look at the pictures of houses below. Use the key to the symbols to work out how much energy each house loses compared with the uninsulated house.
a b c
2 How much energy does each kind of insulation save? Put your answers in a table. (Hint: Carpets save 5%.)
3 Which kind of insulation saves the most energy?
4 Draw a picture of a fully insulated house, using the symbols in the key, and work out how much energy it loses compared with the uninsulated home.
5 Design a leaflet explaining why we should insulate our homes. Include a bar chart to show how much energy the different kinds of insulation save.
[ knowledge, presenting, numeracy ]
8Ie1 Cooling wax 1
In this experiment you will measure the temperature of a liquid as it cools down and turns back into a solid.
- Beaker of hot water - Thermometer
- Tube of hot, waxy liquid - Stop clock
- Test tube rack - Eye protection
- Test tube holder
Take care! The wax will be hot. Use a test tube holder to move the wax from the hot water into the rack.
Copy this diagram into your book and label it using words from the apparatus list.
1 Copy this graph into your book. Continue the line on this graph to show what you think will happen to the temperature.
1 Copy the table on the next page into your book. The time must go up to 20 minutes.
2 Measure the temperature of the hot wax while it is still in the hot water. Write it down in the table.
3 Using a test tube holder take the tube out of the water, and stand it in the test tube rack. Start timing.
4 After one minute, measure the temperature of the wax. Do not stop the clock. Write the result in the table. Look carefully at the wax and decide if it is a solid, a liquid, or a mixture of the two.
5 Take the temperature of the wax each minute and write it in the table.
6 Keep taking the temperature until all the wax has turned into a solid.
2 Record your results in a table like this.
3 Draw a graph of your results. You will need axes like these:
4 a Was the shape of the graph the same as you predicted?
b If not, how was it different?
5 What happened to the temperature of the wax while it was a liquid?
6 What happened to the temperature when the wax was changing from a liquid into a solid?
7 What happened to the temperature when the wax was all solid?
8 What was the freezing point of the wax?
9 Sketch a graph to show what you think would happen to the temperature if you heated the wax up again until it had all melted.
8Ie2 Cooling wax 2
- Test tube rack - Stopclock
- Tube of hot, waxy liquid - Eye protection
Take care! The wax
will be hot. Use a test tube holder to move
the wax from the hot water into the rack.
1 What do you think will happen to the temperature of the liquid as it cools down?
2 Sketch a graph of temperature against time to show what you expect to happen.
3 Will the temperature carry on falling when the liquid is changing into a solid? Give a reason for your answer if you can.
4 Explain what will happen to the particles of the wax when the liquid freezes.
5 Write a method for your experiment. You will need to say how often you will measure the temperature so that you get enough results, and how you will make your investigation safe.
6 Design a results table to show the time, the temperature and the state of the substance. Don't forget that you will need to take a reading at the start of the experiment (at time zero). Now carry out your experiment.
7 Fill in your results table neatly.
8 Draw a graph of temperature against time. Draw a line of best fit. Is it a straight line, a curve, or a bit of both?
9 Does the graph look like your prediction? If not, describe how it is different.
10 Explain what happens to the temperature of the liquid as it turns back into a solid.
11 What is the freezing point of the substance?
12 What would happen to the temperature of the wax if you left the tube to cool for a long time? Would the temperature carry on going down for ever?
13 Sketch a graph to show what you think would happen to the temperature if you heated the wax up again until it had all melted.
[ planning, observing, presenting, considering, knowledge ]
8Ie3 Changes of state
This graph shows what happens to the temperature of a pure substance when it is heated. The diagrams show what is happening to the particles in the substance, and the statements explain what is happening.
Cut out the drawings and statements, and match them up with each other. Decide which ones go with each letter on the graph. Stick the graph into your book, then stick in the drawings and statements in the correct order.
DO not make a double sided photocopy of this worksheet
a The liquid is hotter. The particles are moving around faster, and the liquid has expanded.
1
b The substance has completely melted. The particles are moving around with no fixed arrangement.
c The gas is hotter. The particles are moving around faster.
3
d The solid is hotter. The particles are vibrating more and the solid has expanded.
e The substance is a solid. The particles are fixed in place and vibrating.
5
f The liquid is starting to evaporate. The temperature has stopped going up, because the heat energy is being used to give the particles enough speed to escape from the liquid.
g The solid is starting to melt. Some of the particles have broken away from their fixed arrangement. The temperature has stopped going up, because the heat energy is being used to break the bonds between the particles.
h All the liquid has evaporated.
8Ie4 On the beach
Look carefully at the picture above, then answer these questions.
1 Which things in the picture are receiving energy by radiation?
2 Which things are stopping heat radiation?
3 Which things in the picture are transferring energy by conduction?
4 Which things are stopping heat energy being conducted?
5 Which things in the picture are caused by convection?
[ revision ]
8Ie5 Keeping cool 1
Fill in the gaps using words from the boxes. You may not need to use all the words, and you may need to use some words more than once.
1 The drink is ______________ than the
______________ . Heat energy will flow from the
______________ to the ______________ . When the
______________ in the ice cubes have enough
energy, they will start to break away from their
______________ arrangement, and the ice will start to
______________ .
colder drink evaporate fixed freeze ice cubes melt particles warmer
2 It takes energy to ______________ a solid. When the
liquid freezes and becomes a ______________ again,
this extra energy is given out as ______________ . If
you get molten candle wax on your hand it can be very
painful. The extra ______________ energy produced
when the wax ______________ goes into your hand.
freeze freezes heat light liquid melt melts solid
3 Our bodies need to stay at a constant
______________ . If we get too ______________ ,
we sweat. When the ______________ in the sweat
evaporates, it ______________ the energy it needs
from our bodies. This helps to ______________ us
down. Sweating works even ______________ if there
is a breeze because the ______________ air helps the
sweat to evaporate ______________ .
absorbs better cold cool evaporates faster freezes gives out
hot moving slower temperature water worse
8Ie6 Keeping cool 2
1 Some ice cubes have just been put into a glass of water. The water is at room temperature.
a What will happen to the temperature of the water? Why?
b What will happen to the temperature of the ice cubes?
c Explain why this happens.
2 a Describe the arrangement and movement of the particles in an ice cube.
b How will the arrangement and movement of the particles change as the ice cube absorbs energy from the water?
3 Our bodies produce sweat when we are too hot. Explain how sweating helps us to cool down. (Hint: You will need to think about evaporation.)
4 Sam is heating some water using a Bunsen burner and measuring the temperature with a thermometer that reads from -10 °C to 120 °C.
a What is the highest temperature that the water in the beaker will reach?
b What happens to the energy being put into the water when it has reached this temperature?
c Write a few sentences to explain to Sam why he need not worry about breaking the thermometer by making it too hot.
8Ie7 Relative humidity
Why can you sometimes see your breath on a cold day? Why do some days feel 'muggy' and damp? It is all to do with relative humidity.
The air can only hold a certain amount of water vapour. If there is not much water vapour in the air, water in puddles or sweat can evaporate easily. If the air is holding almost as much water vapour as it can, evaporation happens much more slowly. The amount of water vapour in the air compared to the maximum amount it can hold is called the relative humidity. When the air can hold no more water vapour, the relative humidity is 100%. You can tell when the humidity is high because the air feels 'close' and sweat on your skin does not dry up.
The amount of water vapour that the air can hold depends on the temperature. Warm air can hold more water vapour than cold air. When you breathe, the air inside your lungs absorbs heat energy from your body and its temperature rises. Water evaporates from the fluid lining your lungs, and is taken out of your body when you breathe out. If the air outside your body is cold, your breath cools down. The cooler air cannot hold as much water vapour, so some of it condenses to form tiny drops of water which you can see.
Relative humidity is measured using a 'wet bulb' and a 'dry bulb' thermometer. The difference between the two readings is used to calculate the relative humidity.
1 What is relative humidity?
2 Would you prefer to run a race on a day with a relative humidity of 30% or 90%? Explain your answer.
3 The ground is often wet in the early morning, even if it has not been raining. Why does this happen? (Hint: Think what happens to the temperature of the air at night.)
4 a A wet bulb thermometer usually gives a lower reading than a dry bulb thermometer, even when they are next to each other. Explain why this happens, using ideas about energy and evaporation.
b If the air temperature is the same, would you expect the wet bulb thermometer to give a lower reading on a day of low humidity, or when the humidity is high? Explain your answer.
c Why do you need to take readings from both thermometers to work out the relative humidity?
8I Summary Sheets
Heating and cooling
Heat and temperature
When we know the temperature of something we know how hot it is, not how much heat energy is in it.
Temperature is measured in degrees Celsius (ºC).
Heat (thermal) energy is measured in joules (J).
The amount of heat or thermal energy in something depends upon
- how hot it is (its temperature)
- the material it is made from
- its mass.
Travelling heat
The kinetic theory or particle model of matter helps to explain how some forms of heat energy travel. The theory suggests that everything is made of moving or vibrating particles. When these particles are heated they move faster.
When the particles vibrate faster the material expands.
When the air particles in the balloon are heated, they move apart and the air expands and becomes less dense. This causes the hot air to rise, and the balloon rises too.
Thermal energy can travel in three different ways.
Conduction takes place in solids and can also happen in liquids (although not very well). The particles in a solid are held together tightly. When they gain energy they vibrate faster and the vibrations are passed on. Particles are not as close in a liquid, so conduction is not very good. Metals are the best conductors. Most other solids are poor conductors.
Something which does not conduct heat very well is an insulator. Liquids, gases, and solids which contain a lot of trapped air are insulators.
Convection takes place in liquids and gases.
When the air near the fire is heated, the particles spread further apart and the air becomes less dense and rises. As it rises it meets cooler air and passes the energy on. Having passed on the energy, it cools and becomes denser. The denser air sinks, setting up a cycle or convection current.
Heat can be transferred through empty space by infrared radiation. Radiation does not require the movement of particles. Any hot or warm object gives off or emits radiation. When something takes in heat energy from radiation, it is said to absorb it.
Infrared radiation travels as waves. It can be reflected and it can also be focused.
Changes of state
Substances can change state when they are heated
or cooled. The melting point and the freezing point
of a substance are the same temperature. The
temperature of a substance does not change while it is melting, even if it is still being heated.
8I Target Sheet
Topic
Targets
Before the unit
I have learned this
I have revised this
8Ia
Know another name for heat energy.
Know the units for measuring temperature and heat.
Know that heat energy can be transferred.
Know the difference between temperature and heat energy.
8Ib
Know some examples of heat conductors and insulators.
Be able to explain conduction using the particle model.
Know why some materials are better conductors than others.
Know why some materials are good insulators.
8Ic
Be able to explain expansion and contraction.
Know which substances heat can travel through by convection.
Be able to explain convection currents.
Know which materials infrared radiation can travel through.
8Id
Know why it is important to save energy.
Know why homes should be insulated.
Know how energy can be lost from houses.
Be able to explain how some insulating materials reduce heat loss.
8Ie
Know the meanings of melting, boiling, condensing, freezing and evaporating.
Know the link between melting point and freezing point.
Know what happens to the temperature of a liquid while it is boiling.
Know what happens to the temperature while a liquid freezes.
8I Word Sheets
Word sheets that include new words from the 'Focus on:' pages are available on the Exploring Science website.
8Ia - Hot stuff
Word
Pronunciation
Meaning
degrees Celsius (°C)
sell-see-us
The units for measuring temperature.
heat energy
A form of energy, measured in joules.
joules (J)
The units for measuring energy.
temperature
How hot something is, measured in °C.
thermal energy
Another name for heat energy.
8Ib - Conducting heat
con-duck-shun
The way heat travels through solids.
A material which lets energy flow through it easily.
insulator
A material which does not let energy flow through it easily.
8Ic - Changing size/Going up/Radiation
absorb
To take in energy.
contract
Get smaller.
con-vek-shun
The transfer of heat in fluids.
convection current
A current created by heat causing changes in the density of a fluid.
emit
ee-mit
To give out energy.
expand
Get bigger.
fluid
A gas or a liquid.
infrared radiation
A type of wave in the electromagnetic spectrum. It can travel through transparent things and a vacuum (empty space).
medium
Any substance.
pressure
The force caused by particles hitting a certain area.
The transfer of heat energy by electromagnetic waves.
8Id - Save it!
heat insulator
A material that does not let heat energy flow through it easily.
8Ie - Changing state
boiling point
When a liquid is at its boiling point it is as hot as it can get. It is evaporating as fast as it can.
condense
When a gas turns into a liquid.
evaporate
When a liquid turns into a gas.
gas
Something made of particles that are very spread out and not attached to each other. A gas does not have a fixed shape or volume and is easy to squash.
The hotter something is, the more heat energy it has.
liquid
Something made of particles that are fairly close together, but attached weakly so that they can move past each other. A liquid has a fixed volume but not a fixed shape.
melt
When a solid turns into a liquid.
solid
Something made of particles that are very close together and attached so that they cannot move past each other. A solid has a fixed shape and volume.