In the terminal chapter we looked at thermal systems which transfer energy. This chapter expands on this and looks at the dissimilar means that thermal energy is transferred betwixt dissimilar objects.
It is important to understand the difference between oestrus, as a concept, and temperature. Temperature is a measure of how hot or cold an object is; it is a mensurate of the boilerplate kinetic energy of the particles of a substance. Oestrus is the free energy transferred between 2 objects as a upshot of the temperature departure betwixt them. It is too true when free energy is transferred between a organisation and the surroundings as a consequence of the temperature difference between them. Temperature is measured in degrees Celsius (°C) or degrees Kelvin (1000) while heat is measured in joules (J).
three.1 Heating as a transfer of energy (0.5 hours)
3.2 Conduction (two hours)
Tasks
Skills
Recommendation
Activity: Conduction through a metal rod
Experimentation, observation
Suggested
Investigation: Do all materials conduct heat in the same way?
Hypothesising, investigating, evaluating
Suggested
Investigation: Which metals are the best conductors of rut?
What is the difference between heat and temperature?
How does a heater warm up a cold room?
Why can the Sun make the states warm?
Why does my cold drink become warm?
Heating as a transfer of free energy
thermal
heat
temperature
In the last chapter we looked at thermal systems. The thermal energy of an object is the amount of energy it has inside of it, in other words, its internal energy. In a thermal system, thermal free energy is transferred from one object to some other. Estrus is the transfer of thermal energy from a arrangement to its surround or from ane object to another. This transfer of energy is from the object at a college temperature to the object at a lower temperature.
It is very important to know that, in science, heat and temperature are not the same thing.
Heat is the transfer of thermal energy from a organization to its surround or from one object to another equally a result of a difference in temperature. Heat is measured in joules (J). This is considering rut is a transfer of energy.
Temperature is a measure of how hot or cold a substance feels and information technology is measured in degrees Celsius (°C). Temperature is a measure of the boilerplate kinetic energy of the particles in an object or arrangement. We use a thermometer to measure the temperature of an object or substance.
Complete the following table to summarize the differences between heat and temperature
Heat
Temperature
Definition
Unit of measurement
Symbol for unit
Here is the completed table:
Heat
Temperature
Definition
The transfer of energy from a hotter object to a colder object, or from a system to its surroundings
A measure of how hot or cold a substance feels. A mensurate of the boilerplate kinetic energy of the particles of a substance.
Unit
Joules
degrees Celsius
Symbol for unit
J
°C
Heat is the transfer of energy. During free energy transfer, the energy moves from the hotter object to the colder object. This means that the hotter object will cool downward and the colder object volition warm up. The energy transfer will continue until both objects are at the aforementioned temperature.
There are 3 means in which thermal energy can be transferred from one object/substance to another, or from a arrangement to its environment:
Conduction
Convection
Radiation
A rap vocal to introduce you to (and help you lot remember!) conduction, convection and radiation.
Allow's have a await at these in more particular.
Conduction
conduction
usher
insulator
A suggestion to innovate this topic is to ask learners what happens to a metal teaspoon when they put it in their hot beverage. If possible, demonstrate this briefly in class, fifty-fifty with a hot glass of water and a metal rod. In addition, use a plastic teaspoon to demonstrate the difference as plastic is an insulator.
Have y'all noticed that when yous put a cold, metallic teaspoon into your hot cup of tea, the teaspoon handle also warms up after a while? Take you ever wondered how this warmth "moved" from the hot tea to the common cold teaspoon and warmed it up? This is one way in which energy is transferred and this is called conduction. Permit'due south find out how it works.
How does the handle of the metal teaspoon go hot when in a cup of tea?
When energy is transferred to an object, the free energy of the particles increases. This ways the particles accept more kinetic energy and they outset to motility and vibrate faster. As the particles are moving faster they "crash-land" into other particles and transfer some of their energy to those neighbouring particles. In this way, the free energy is transferred through the substance to the other terminate. This process is called conduction. The particles comport the energy through the substance, every bit shown in the diagram.
Let'southward demonstrate this practically.
Conduction through a metallic rod
Set this demonstration up in front of the class equally you offset to talk about conduction.
MATERIALS:
Bunsen burner
metal rod
Vaseline
paper clips, drawing pins or safety pins
two wooden stands, or a stack of books or blocks of woods to create the two stands on either side
2 pegs
INSTRUCTIONS:
Set the apparatus upwardly every bit shown in the diagram.
Cover the rod in Vaseline and place information technology between the 2 stands with pegs to prevent it from rolling and agree information technology in identify. The rod must exist extending past the left hand upright and the Bunsen burner placed here so that the Vaseline does not melt due to radiation from the Bunsen burner, but rather conduction along the metallic rod.
Attach the paper clips or cartoon pins to the rod by sticking them into the Vaseline.
Light the Bunsen burner and oestrus the 1 end of the rod.
Watch equally the paper pins or pins drop off ane past i as the free energy is conducted through the rod.
INSTRUCTIONS:
Your teacher will set upwardly the demonstration as in the diagram below.
Observe what happens to the pins or paper clips as the Bunsen burner is lit and heat is practical to ane end of the metal rod.
As an extension exercise you could include another investigation in which yous measure the charge per unit of energy conduction forth a metallic rod. Repeat the experiment placing drawing pins at 5cm intervals on a long metal rod. Clamp the metal rod and heat one end over a Bunsen burner. Utilise a stopwatch to time how long it takes for each drawing pin to drop and record the results on a graph. This could be farther extended by using dissimilar metals and putting all the results on a single set of axes. The gradient of the graphs would requite the rate of heat conduction.
QUESTIONS:
When the Bunsen burner is lit, what happens to the rod merely above it?
Energy is transferred to the metallic of the rod merely above it. The thermal energy of this role of the rod increases and the rod becomes hot.
Which pivot or paperclip dropped off the metal rod beginning? The one closest to or furthest from the Bunsen burner?
The i closest to the Bunsen burner dropped off first.
What does this tell the states about the way in which oestrus is conducted along the rod?
The heat is transferred from where it is hottest to the colder terminate of the rod.
Let'due south think about the teaspoon in the tea once again. The tea is hot and the metal spoon is cold. When you put the metal teaspoon into the hot tea some of the thermal energy from the tea is transferred to the metal particles. The metal particles offset to vibrate faster and collide with their neighbouring particles. These collisions spread the thermal energy up through the teaspoon. This makes the handle of the teaspoon experience hot.
Conduction is the transfer of thermal energy between objects that are touching. In the teaspoon case, the particles of the tea are touching the particles of the metal spoon, which in plow are touching each other, and this is how rut is conducted from i object to the other.
Do all materials conduct rut in the same way? Allow'south find out.
Misconceptions nearly temperature. Why practice you recall your carpeting feels warmer than tiles in winter? Picket this video to find out.
In response to the video in the margin box well-nigh why your carpet feels warmer than the tiles in winter, y'all can come up back to this question after you lot have performed the following investigation, and likewise looked at the instance of the cake tin can and the cake straight out of the oven. You lot can atomic number 82 the discussion in the following style:
Get-go off by asking learners why they would prefer to stand up on a carpet in wintertime rather than the tiles. They would probably answer that the rug feels warmer.
Follow this upward by asking them what they remember the temperatures of each surface is. Learners might say that they remember the tiles are at a lower temperature than the carpet considering it feels colder. This is incorrect as the tiles and the carpet will be at the same temperature equally they have both been in the same surround for a while and so volition be at the same temperature.
However, if you pose this question to learners over again afterwards doing the following investigation and likewise later on looking at the block and cake tin example, they might then realise that this is another example of a difference in electrical conductivity.
Namely, the tiles and the carpet are both at the same temperature, simply the tiles are a ameliorate conductor of energy so they conduct heat at a faster rate away from your feet than the rug would, making the tiles experience colder, when in actual fact they are at the same temperature.
Do all materials conduct estrus in the aforementioned way?
This investigation will show the learners that metals bear oestrus better than non-metals. If possible, lookout man the Veritasium video provided in the visit link before class well-nigh the misconceptions surrounding temperature and which demonstrates this activity. Start off by asking learners to feel the blocks and ask which 1 feels colder. The aluminium block will feel colder. Then inquire them which cake they think will melt the ice cube the fastest. as in the video, about people think that the ice cube will melt faster on the plastic block as information technology feels warmer than the aluminium block. However, this is a misconception, and will be demonstrated in the activity that it is in fact the aluminium block which causes the water ice cube to cook faster as metals are a improve conductors of estrus.
AIM: To investigate which materials are the best conductors of heat.
In this investigation, we will be placing an water ice cube on a plastic block and on an aluminium block and observing which ice cube melts the fastest.
HYPOTHESIS: Write a hypothesis for this investigation. Which cake do y'all think will cook the ice cube the fastest?
Learners might hypothesize that the ice cube will melt faster on the plastic than the aluminium block. If they practice, make certain that they come back to reject their hypothesis and revise information technology.
MATERIALS AND APPARATUS:
a plastic block
an aluminium block
ice cubes
a plastic ring to proceed the ice cube in place on the block
Y'all tin can use whatsoever piece of plastic and aluminium (or other metal) that you can notice. if possible, use a round ring to end the melted water from spilling.
METHOD:
First feel the plastic block and the aluminium block. Describe how they experience.
Learners will annotation that the plastic block feels warmer than the metal cake.
Place an ice cube onto each block and observe what happens.
OBSERVATIONS:
Which ice cube starts to cook showtime and the fastest?
The ice cube on the aluminium/metal cake melts start.
Is this what you thought would happen? Refer dorsum to your hypothesis.
Learner-dependent answer. Well-nigh people generally have the misconception that the ice cube will melt faster on the plastic block, rather than the metal block.
CONCLUSIONS:
What can you conclude most which textile (the plastic or the metal) is the all-time conductor of heat?
Metal is a better conductor of heat than plastic as the ice cube on the metal melted kickoff.
Nosotros volition talk over this in the next paragraph most why this happens.
And so how does this work? This is to do with thermal conductivity, the charge per unit at which heat is conducted from one object to another.
When you lot originally felt the blocks, you felt that the plastic block was warmer. But, what we observed is that the aluminium or metal block melted the ice cube faster. This is considering the metal cake is conducting the heat faster to the water ice cube. The plastic block is a worse thermal usher so less heat is being transferred to the water ice cube and then information technology does not melt as fast.
Why then does the aluminium block feel colder than the plastic block?
This is considering the aluminium conducts oestrus faster away from your hand than the plastic does. Therefore the aluminium block feels colder and the plastic block feels warmer. When you touch something, you practice non actually feel the temperature. Rather you feel the charge per unit at which heat is either conducted away from or towards you.
Let'southward think of another instance of blistering a cake. Imagine yous take merely finished baking a block in the oven at 180 °C.
A cake blistering in the oven in a metal tin.
When you remove the cake from the oven, which is more than likely to burn yous more, the metal cake tin, or the cake?
The most likely reply is that the cake tin can will give you a more serious burn.
For the next question, go learners to speculate about what they think nearly the temperature of the block tin and the bodily tin. Many people have the misconception that the tin can is hotter than the cake as it feels hotter. They are actually at the same temperature as they have both been baking at 180 °C.
Do yous call back the cake and the tin are at the same temperature when yous remove them from the oven? Why?
Yes, the cake and the tin are both at the same temperature as they take been blistering at 180 oC. Learners might be inclined to say that the tin is at a higher temperature than the block as it feels hotter and the metallic tin can volition give you lot a more than serious burn down than the actual cake. This is a misconception and yous must discuss this. As with the example of the aluminium and plastic block, the cake tin and the cake are at the aforementioned temperature. Only, the metallic tin conducts heat faster towards your hand than the block does. Therefore, the metal tin will feel hotter and is more than likely to requite you a serious burn than the cake does. When you touch something, you practise not really feel the temperature. Rather you feel the rate at which oestrus is either conducted abroad from or towards you.
If yous accept the opportunity, spotter the video in theVisit margin box past typing the link into your internet browser, even on your mobile phone. This video demonstrates the cake and cake tin instance.
What we have seen here is another example of thermal conductivity. The tin will deport rut much faster to your hand than the cake, so the tin can will burn you, only the block volition non. The tin and the block are at the same temperature.
So what have we learnt? Metals conduct heat better than non-metals.
In that location are substances that allow thermal energy to exist conducted through them and so they are chosen conductors.
There are substances that do not allow thermal energy to be conducted through them and then they are called insulators.
This links back to what we learned in Matter and Materials about the properties of materials and how their properties decide their uses. Remind learners of the activities they did in Matter and Materials, specially linked to electrical conductivity.
Remember, just because a textilefeels colder, does not mean it has a lower temperature. It may just exist that information technology is conducting rut faster away from your manus.
At present that nosotros know that metals are good conductors of estrus, do you lot think all metals conduct rut equally well? Let's investigate which metals are better conductors.
Which metals are the all-time conductors of heat?
We are going to see which metal is the improve conductor of thermal energy. To do this we will see which metal becomes hot starting time.
Brand sure y'all know how to apply a Bunsen burner safely.
At present that we have established that metals conduct rut energy better than non-metals, the learners will investigate which metals are the best conductors of oestrus. This investigation requires more heat than the previous i so the learners should not test the conduction with their fingers.
Spend a few minutes before the learners begin past demonstrating the right procedure for lighting a Bunsen burner. There are many different instructional videos on the internet, such as the one identified in the visit box in the margin. Here are a listing of instructions for your reference:
Ensure that you are working on an advisable surface, such as a fireproof mat, and that it is clean and uncluttered.
Make sure that the gas tube is in practiced status and not perishing.
Connect the to the gas outlet securely and make sure it won't easily come off if moving the Bunsen burner around.
Make sure that the collar at the base of the Bunsen burner and the air pigsty are closed.
First light your match, holding information technology away from the Bunsen burner.
Turn on the gas with your other hand and bring the match to the Bunsen burner to light it.
Adapt the air hole by opening information technology so that the flame becomes hotter.
Adjust the intensity of the flame using the collar at the bottom.
You tin can ask the learners to draw posters explaining how to light a Bunsen burner as an additional exercise if yous feel they demand the extra practice and reminders.
Retrieve that the tripods and metallic rods that the learners employ will go quite hot during this experiment. Make sure to allow the apparatus to cool before packing it away.
AIM: To identify whether some metals are better conductors of heat than other metals.
Identify VARIABLES :
Read through the method and look carefully at the diagram for the investigation to identify the unlike variables required.
Which variable are you going to change?
Material being tested i.e. iron, copper, contumely or aluminium
What practise we call the variable that you are going to modify?
This would be the independent variable
Which variable are yous going to measure?
Time taken for the drawing pin to drop.
What do we telephone call the variable that you are going to measure?
Which variables must be kept the same?
Length and thickness of the cloth should be the same for each material used. Distance of the cartoon pin from the heat source.
What practise we call the variables which must be kept the same?
HYPOTHESIS:
Write a hypothesis for this investigation.
Learner-dependent answer. Learners can hypothesise about which metal they think will exist the best conductor, for instance, the copper rod will be the best conductor.
MATERIALS AND APPARATUS:
Bunsen burner
Vaseline
copper, iron, brass and aluminium rod
stopwatch
drawing pins
tripod
cardboard or paper
matches
The materials listed hither are a suggestion. You can utilise alternative apparatus to notwithstanding do this investigation. For case, a spirit burner could also exist used to oestrus the rods. If you practise not accept a tripod stand, yous can place the metallic rods on some other stand up, such as a block of woods, with the ends sticking out 1 side to still attain over the Bunsen burner. Paper clips can likewise exist used instead of cartoon pins. The type of metals are non of import equally long equally yous have different metals of the same length.
METHOD:
Stick the flat end of a cartoon pin to the end of each of the metal rods using the Vaseline. Try to use the same corporeality of Vaseline for each drawing pin.
Identify the cardboard on the tripod.
Balance the metal rods on the paper-thin then that i terminate of each is over the Bunsen burner.
Low-cal the Bunsen burner.
Using a stopwatch, measure how long information technology takes for each of the pins to drop off.
Tape your results in the tabular array.
Describe a bar graph to illustrate your results.
The cardboard is an insulator and will finish the heat from the rods transferring to the tripod itself. The loss of heat from the rods could affect the results.
RESULTS AND OBSERVATIONS:
Tape your results in the following table.
Type of metal
Time taken for pin to drop off (seconds)
iron
copper
brass
aluminium
Now depict a bar graph to bear witness your results. Do not forget to give your graph a heading to describe what information technology represents.
Which variable should exist on the horizontal ten-centrality?
The type of material should be on the horizontal axis. This is the independent variable.
Which variable should be on the vertical axis?
The time taken for the cartoon pin to to fall off should be on the vertical centrality. This is the dependent variable.
Why do you remember that a bar graph is suitable for this investigation?
The contained variable/type of textile is not a number value and then it does not need a number line. A bar graph is used to correspond non-number or non-continuous data.
The independent variable is always drawn on the x-axis with the dependent variable on the y-axis. Both axes must be labelled and show the units of measurement. The graph should have a heading.
An example set of data is given hither with the accompanying bar graph as a reference. Your results may vary from these presented here.
Type of metal
Time taken for pin to drop off (seconds)
atomic number 26
lx
copper
30
brass
50
aluminium
40
ANALYSIS :
Which bar on your graph is the longest?
The longest bar should be the fe.
Which bar is the shortest?
The shortest bar should be the copper.
Write down the materials in social club of how fast they conducted estrus from the quickest to the slowest.
Activity-dependent answer.
Why does the Vaseline cook?
The estrus is transferred by conduction through the metal rod and to the Vaseline causing an increase in its temperature so a change of state (solid to liquid).
Why exercise you lot think it was necessary to place the piece of cardboard or paper on the tripod stand underneath the metal rods. Hint: The tripod stand is too made of metal.
The cardboard acts as an insulator to prevent estrus from transferring to the stand up from the rods. For the purpose of this experiment, the heat should transfer down to the unlike metal rods only.
Why do you think it is necessary to use the aforementioned corporeality of Vaseline on the ends of each rod?
This is and so that the test is fair, otherwise some drawing pins might be stuck on better than others, leading to inaccurate results.
Exercise you lot recollect we could have performed this investigation if our rods were of different lengths? Why?
No, otherwise it would not be a fair exam as the rut volition take to be conducted further in some rods than in others, leading to inaccurate results.
EVALUATION:
Information technology is ever important to evaluate our investigations to see if in that location is annihilation we would alter or meliorate on.
Is there anything that went incorrect in your investigation that you could have prevented?
Learner-dependent answer.
If you were to repeat this investigation, what would you lot change?
Learner-dependent respond. Examples include: repeating the aforementioned experiment three times and averaging the results, increasing the number of metals tested.
CONCLUSIONS:
Write a conclusion for this investigation about which metal is the best usher of heat.
This answer volition depend on their experimental results, and the exact metals which y'all used in the investigation.
In this section we looked at how heat is conducted through metallic rods and other objects. These were all solid objects. How is free energy transferred through liquids or gases? Let'southward notice out in the next department.
Convection
convection
convection current
As an introduction to this section, you tin can simulate the "sitting in a bath" concept past filling a rectangular plastic tub or small water tank with cold h2o and then pouring hot h2o into i side. Invite the learners to experience the cold side of the tub and then feel it a few minutes afterward.
If you lot can get agree of a lava lamp, this tin can make a very exciting introduction to the lesson. You can plow the lights off and identify the lava lamp on your desk for when learners come up into the course. You tin can then explain that y'all are going to detect out why the blobs ascension and then fall back down in the lava lamp. If you do not take a lava lamp, yous can too play this video:
Think of a pot of water on a stove. Only the bottom of the pot touches the stove plate, only all of the h2o within the pot, fifty-fifty the water not touching the sides, becomes warmer. How does the energy transfer throughout the water in the pot? The transfer of energy is because of convection.
Let's practise an action that volition help us to visualise how convection occurs.
Convection in h2o
Colourful convection currents (video)
MATERIALS:
200 ml drinking glass chalice
potassium permanganate
Bunsen or spirit burner, tripod stand up, wire gauze
Take note that you only need a few grains of potassium permanganate, otherwise yous volition not run across anything.
An alternative to the higher up materials is the following:
Cut the cervix of a transparent 4 or 5l container.
Fill the container three quarters with common cold tap water.
Put coloured hot h2o (can be coloured with food colouring) into a small bottle with a hat that is like shooting fish in a barrel to remove. Close the lid.
Lower the small canteen into the container.
Gently open up it once lowered, and so gently take out your mitt from the container, with the lid.
Observe that the coloured hot h2o rises from the minor bottle, through the cold water, then drops downwardly again every bit it cools on its manner up - observe the convection currents.
INSTRUCTIONS:
Learners must not just throw the potassium permanganate into the h2o. It is important that they place it carefully in 1 side of the bottom of the beaker so that they tin can run into how the currents in the water move.
Half fill up the chalice with cold tap water.
Carefully put a small amount of potassium permanganate on one side of the beaker. Practice Not STIR.
Heat the water directly under the side of the beaker with potassium permanganate with a Bunsen/spirit burner and observe what happens.
Set upward a command experiment and place a few grains of potassium permanganate into the lesser of a beaker filled with water. Do non heat this beaker and detect what happens.
QUESTIONS:
What did you see as the water started to warm up in the beaker that was heated? Describe a moving-picture show to prove what you run into.
Learners should see the imperial from the dissolved potassium permanganate moving in a circle up through the water.
What is happening to the potassium permanganate in this beaker?
As the potassium permanganate dissolves in the water information technology is being dragged through the water.
Tin can you explicate the blueprint you saw?
The warm h2o is ascent and beingness replaced by cooler h2o.
NOTE:
At this point the learners are not aware of the theory behind convection currents and and so their answers will be quite elementary.
Compare this to the beaker which was non heated. What did you observe in this beaker?
The potassium permanganate will dissolve, but information technology will non form rising currents. Information technology will diffuse evenly and densely at the bottom of the beaker. Over a long time it will spread out evenly throughout the water.
Allow'due south at present explain what we observed in the final activeness. Convection is the transfer of thermal energy from one place to another by the motility of gas or liquid particles. How does this happen?
Equally a gas or liquid is heated, the substance expands. This is because the particles in liquids and gases gain kinetic energy when they are heated and get-go to move faster. They therefore accept up more space as the particles move further apart. This causes the heated liquid or gas to move up and the colder liquid or gas moves downwards. When the warm liquid or gas reaches the pinnacle information technology cools downwards again and therefore moves dorsum down again.
We then say that the heated liquid or gas is less dumbo as the same particles are at present taking up a larger space. Nosotros will learn more about density adjacent twelvemonth in Gr eight.
In the last activity, the water particles gained kinetic free energy and moved autonomously from each other, therefore taking up more space. This water and so moves upwardly every bit it is less dumbo than the cold h2o, meaning it it lighter than the cold water. We were able to observe this equally the potassium permanganate dissolved in the h2o and moved with the water particles, and and so moved downwards again every bit the water cooled.
This motion of liquid or gas, is chosen a convection current, and free energy is transferred from ane expanse in the liquid or gas to another. Accept a look at the diagram which shows a convection electric current.
Does smoke motility upwardly or down?
The learners demand to be careful with this experiment. Information technology is like shooting fish in a barrel to prepare the T-shaped cardboard alight with the candle and they should be conscientious not to burn their fingers when lighting the candles too.
MATERIALS:
T-shaped cardboard
candle
twist of paper or splint
beaker
box of matches
INSTRUCTIONS:
You can drip some wax onto the base and so stick the candle onto this to make it stand.
Light the candle and place it within the beaker, to the side of the beaker.
Put the T-shaped cardboard into the beaker so that in that location is a small-scale gap between the lesser of the beaker and the cardboard.
Light the twisted ringlet of newspaper and hold it in the chalice on the reverse side to the candle as shown in the diagram.
Notice what happens to the smoke.
QUESTIONS:
What happens to the fume from the newspaper?
The smoke is drawn downwardly under the cardboard and up next to the candle.
Annotation:
Some of the smoke particles may move upwards.
Why do you think the fume moves in this way?
The candle heats the air in a higher place it which creates a convection electric current which draws the libation air on the other side of the cardboard towards the candle. This motion of the air particles pulls the smoke particles with it. The fume particles allow usa to visualise the convection current.
In the last two activities, nosotros take observed convection currents in a liquid and in a gas. Convection currents can simply form in gases and liquids as these particles are gratis to move around. They are not held in fixed positions like in a solid. Solid particles are held together too tightly for them to move when heated. Solid particles will only vibrate faster when heated merely will non motion from their positions.
The solid particles will only move from their positions when they have gained enough kinetic energy for a change of state to occur and the solid melts to become a liquid.
The blobs in a lava lamp move up and downwards in the lamp every bit they first oestrus and expand and then reach the surface and absurd and so they move dorsum down again.
The blobs in a lava lamp move upwards and downward showing us the convection currents equally the lamp provides the source of heat at the lesser.
How does a lava lamp work? (video)
Now that nosotros have learned nearly convection, how tin nosotros apply this in the globe around us? Information technology is interesting to learn about concepts and theories in scientific discipline, but it is even more interesting when we find how this has an influence in our daily lives.
Installation of air heating and cooling systems
Imagine that your instructor has been given a heater and an air-conditioning unit of measurement for your classroom. The heater volition warm your classroom in winter and the air-conditioner will keep you cool in summer. You demand to help yous teacher decide where each item should become in the classroom. Should they continue the wall nearly the ceiling or near the floor? Should they get adjacent to a window?
This is an photo of an air conditioner.
INSTRUCTIONS:
Get into groups of two or iii.
Hash out where in your classroom you would place a heater then that it can finer heat up the room. Draw a diagram to explain your choice.
A heater should be placed near the floor. Every bit information technology heats the air around it, the warm air will rise and be replaced past cool air. The cool air is so warmed and rises. This creates a convection current which volition warm the entire room. The diagram should show the upwardly apportionment of the warm air.
Discuss where in your classroom y'all would install the air-conditioner so that it can finer cool the room. Draw a diagram to explicate your choice.
An air-conditioner should be placed near the ceiling. As information technology cools the warm air near the ceiling the absurd air moves downward towards the floor and is replaced by warm air from below. The warm air is then cooled by the air-conditioner. This creates a convection electric current which volition cool the entire room. The diagram should prove the down circulation of the cool air.
Endeavor to discover an air-conditioner or heating specialist who you can interview. Ask them to explain the best way to install the air-conditioner and a heater.
We have now looked at how energy is transferred through dissimilar materials, whether they are solids (conduction) or liquids and gases (convection). Just, what about if there are no particles to transfer the thermal free energy? Is there still a way for free energy to exist transferred?
Radiation
radiation
matt
reverberate
blot
Have yous always wondered how the Dominicus is able to warm the states even though it is so far away? The free energy is transferred from the Sun to everything on the Earth. The Sun does not need to be touching the Earth for the energy to be transferred. Also, there is infinite in between the Earth and the Sun. The energy from the Sun is able to warm united states without the Lord's day ever touching u.s..
This transfer of energy is called radiation. Information technology is unlike to conduction or convection as it does non require objects to be touching each other or the movement of particles.
Radiations comes from the Greek discussionradius, meaning a beam of light.
The Sun radiates heat in all directions. Energy is transferred through infinite to Globe
Information technology takes light nigh 8 minutes to travel from the Lord's day to Globe.
We can also encounter how heat is transferred by radiation here on Earth, and non merely between the Sun and the Earth. Let's demonstrate the deviation between radiation and convection using a candle.
Radiation from a candle
A suggestion is to do this every bit a sit-in and get learners to come up up in pocket-sized groups. You lot can and then control how close they put their hands to the flame. Have note that heat radiates in all directions around the source of thermal free energy (including the summit of the candle). What makes us experience the oestrus more at the top is the effect of convection currents of the hot air moving upward. They should outset hold their hands in a higher place the flame to feel the heat from convection. Then they should hold their hands next to it to feel the heat transfer from radiation. Finally, you can also demonstrate conduction using a metal spoon and holding it in the flame.
MATERIALS:
candle in a holder
metal spoon or metallic rod
matches
INSTRUCTIONS:
Calorie-free a candle and place it in a holder. Your teacher might practice this and get groups of you lot to come up up at a time to the demonstration.
First hold you hand in a higher place the candle.
Then hold your hand on the side of the candle.
Answer the following questions.
QUESTIONS:
We know now that heat from a candle will be transferred to the air around information technology. These will warm up. Where will this air move to?
The air particles will motion upwards.
So, when you agree your manus above the candle, what practise you feel and why?
When you hold your hand above the candle, the warm air particles transfer the free energy to your paw causing your hand to warm upwards and you lot feel the increase in temperature.
Only, what virtually when you hold your mitt on the side of the candle? Could you also feel warmth from the candle?
This is not convection equally the air particles practice not travel sideways when they warm up from the flame. So, how is energy transferred to your mitt when y'all feel the warmth on the side of the candle?
The energy is transferred past radiation.
Lastly, if your teacher placed a metal spoon in the candle flame and yous felt the end, how would it experience afterwards a piddling while?
How was the energy transferred from the flame to the cease of the spoon?
The energy was transferred by conduction.
This photograph shows all iii forms of how rut is transferred. Explain which type of estrus transfer is represented by each manus.
Energy is transferred in 3 ways.
The hand on the right holding the spoon represents conduction every bit the heat is transferred from the flame through the metal of the spoon. The hand in a higher place the candle represents convection as heat is transferred from the flame by moving air particles which warm upwardly and rise. The hand in a higher place the candle volition as well experience heat from radiation as heat is radiated in all directions. The hand on the left next to the candle represents radiation as energy is transferred from the source through space to the manus.
As we saw in the last activity, free energy is transferred from the candle to your hand by convection and by radiation. Have yous ever stood next to a huge burn? You volition feel the radiating heat even though the air might be very common cold. This is because the energy is transferred to you by radiation through the spaces between the particles in air.
What about if y'all touch a blackness wall or a white wall? Practice you think in that location is a deviation in how different surfaces absorb and reflect radiations? Permit's find out by doing an investigation.
Which surfaces blot the nigh radiation?
This investigation looks at the way different materials absorb radiations or reverberate it. It is important that the surface expanse of each material is kept the same so that the results are reliable. This investigation will work best on a hot, sunny twenty-four hours. Try to detect the sunniest identify you lot tin can on the school grounds in order to conduct this investigation.
Nosotros are going to investigate which surfaces absorb the most heat, using nighttime coloured paper, lite coloured paper and shiny paper, such as aluminium foil. Nosotros will utilise the temperature inside an envelope made from each kind of paper as a measure of the amount of oestrus the paper absorbed. Why exercise y'all remember we can exercise this?
Discuss this with your grade as it is of import that the empathize why they are doing the investigation. When the newspaper envelope absorbs oestrus, the free energy volition so be transferred to the air inside the envelopes. This will and so cause a ascension in temperature which the thermometer will show. The more energy that is absorbed, the more that is transferred to the interior, and the higher the temperature. The paper that reflects the nigh energy will show the smallest increase in temperature.
INVESTIGATIVE QUESTION:
Which surfaces will blot the most radiation from the Sun and therefore increase in temperature the fastest?
VARIABLES
Which variable are you going to measure?
The temperature of the substance.
What do we telephone call the variable you lot have measured?
Which variable are yous going to modify?
What practise nosotros call this variable?
What must be kept the same for all the different materials?
The surface area of each substance which is exposed to the Sun must be the same (ie. the size of the envelope). The length of time that the materials are exposed to the Lord's day.
HYPOTHESIS:
Write a hypothesis for this investigation.
Learner-dependent answer. The hypothesis could be: 'The shiny surface will absorb the least heat, and the black/dark coloured paper will absorb the most.'
MATERIALS AND APPARATUS:
matt black newspaper
white paper
aluminium foil
3 alcohol thermometers
stopwatch or timer
gum or adhesive record
Y'all can also extend the investigation past testing more colours, such as cherry and yellowish to meet how they compare.
METHOD:
Fold each piece of paper and aluminium foil into the shape of an envelope.
Put a thermometer into each of the envelopes and record the starting temperature.
Put all the envelopes outside in the Sun.
Cheque the temperature on the thermometers every two minutes for 16 minutes.
Record your results in the tabular array.
Draw a line graph for each envelope on the same gear up of axes.
RESULTS AND OBSERVATIONS:
The results for this experiment are dependant on the size of the newspaper envelope that the learners make too as the amount of sunlight falling on the envelopes. The readings may also fluctuate from fourth dimension to time as a result of cloud covering.
Record your results in the following table.
Time (minutes)
Temperature in black paper envelope (°C)
Temperature in white newspaper envelope (°C)
Temperature in aluminium foil envelope (°C)
0
2
4
6
8
10
12
xiv
16
Describe a line graph for each of the envelopes in the space below. Do not forget to give your graph a heading.
Fourth dimension should be plotted on the horizontal axis with temperature on the vertical axis. Draw three different graphs for the three dissimilar materials. Comparing the slopes of the three graphs volition allow the learners to determine which material warmed up fastest. The line with the steepest slope heated the fastest.
The black newspaper should increase in temperature the fastest so it would have the steepest curve. The aluminium envelope should increase in temperature the slowest and have the shallowest curve, with the white paper in between.
The graph should have a title. An case of a suitable title would exist 'A comparing of the charge per unit of temperature increase of different surfaces.'
ANALYSIS:
What do you lot notice about the shapes of the graphs you drew? Are the graphs straight lines or curves?
Activity-dependent respond. The values obtained volition depend on the size of the envelopes the learners brand besides as the amount of sunlight to which the envelopes were exposed. Information technology is important that they should come across an increasing trend in the lines of the graph.
Which line on your graph is the steepest? What does this tell u.s.?
The graph representing the black paper should be the steepest graph. This ways this envelope increased in temperature the fastest. This is because the blackness, matt colour absorbs the most radiation.
Compare your results for the white newspaper and the shiny surface. What does this tell you.
The envelope made out of aluminium foil should evidence the smallest increase in temperature as shiny surfaces reverberate oestrus.
EVALUATION:
Did the investigation run smoothly? Or is there annihilation you would change?
Learner-dependent answer. Learners should talk over the quality of their method and whether they got the results that they expected to get. They could propose repeating the experiment three times and getting an average increase over time.
Did you get any results which did not seem to fit the overall blueprint?
Learner-dependent reply. Some learners may become outliers simply others may have clear results with a clear patterns.
Decision:
Write a decision for your investigation. Remember to refer back to the investigative question that we wanted to respond.
Learners should conclude that black surfaces absorb the most radiation and therefore show the biggest and fastest increase in temperature, whereas shiny surfaces absorb the least, as they reflect the most.
Radiation from the Sunday is essential to life on Earth, simply ultraviolet radiation from the Sun can also be very damaging our pare. Retrieve to wear suncream and a hat when outside and avoid being in direct sunlight between 11am and 2pm.
The investigation showed that the dark envelope showed the biggest increase in temperature. The lighter coloured envelope showed a smaller increase in temperature. The envelope fabricated out of a shiny cloth showed the smallest increase in temperature.
And so what accept we learnt? Dark colours seem to absorb more of the Sun'southward radiation than lite or cogitating colours. Then, if you want to stay warm on a cold day, dark wearable will absorb more than of the available warmth from the Dominicus's radiation than lite colours.
The average summer temperature in Hotazel, a town in the Northern Cape is nigh 34 °C. If yous lived in Hotazel and needed to buy a new automobile, would you lot buy a light or dark-coloured car? Explicate why.
The best colour to buy would exist a white machine because, as seen in the investigation, light colours absorb less heat than dark colours. So a light-coloured car will ideally remain the coolest on the inside.
You have the option of getting the machine sprayed to make the surface more shiny. Exercise yous think this will help go on the motorcar cool in hot, summer months? Explain why.
Yes, information technology will help, as shiny surfaces are more reflective and then more than radiant heat is reflected rather than absorbed, keeping the inside of the car cooler.
Summary
Estrus is energy that is transferred from a hotter to a libation object.
Temperature is a measure of how hot or cold a substance feels.
Rut (free energy transfer) occurs in 3 ways: conduction, convection or radiations.
During conduction, the objects must be touching each other for energy transfer to take place.
Some materials, such as metals, conduct heat well. They are chosen conductors of rut.
Some materials, such as plastics and woods, wearisome down or prevent conduction. They are called insulators.
Convection is the transfer of energy within liquids or gases.
A convection electric current refers to the movement of a liquid or gas during energy transfer. The liquid or gas moves upwards from the oestrus source (equally it expands) so downwards when the liquid or gas cools (every bit it contracts).
Radiation is the transfer of energy where objects do non have to be physically touching. Radiations does non require a medium and can take place through empty space.
The Lord's day's free energy is transferred to Earth by radiation.
Dark, matt surfaces are good absorbers of radiant heat
Light and shiny surfaces are poor absorbers of radiant heat. Light, shiny surfaces reflect more radiant heat than they absorb.
Concept map
Below is a concept map showing how the unlike topics about heat together. You need to make full in the iii different means that energy can exist transferred, every bit discussed in this chapter, simply you lot cannot just put anyone into any box. You need to study the concepts which come after and explicate each way of transferring energy during heating.
Revision questions
How is energy being transferred in the following photos showing different heating processes? Write down conduction, convection or radiation. Some illustrations may prove more than than ane form. [4 marks]
The heat from the Sun travels to Earth.
Cooking food on a braai or burn down.
Radiation
Convection (and also some radiation)
Boiling water in a metallic pot.
A heater in a room.
Conduction (through the metal) and convection (in the water)
Radiation and convection
In each of the following situations, identify the method of energy transfer taking place (conduction, convection, radiation).
A fireplace has a drinking glass screen in forepart of information technology. The person sitting in a chair next to the fireplace chair feels hot due to ________. [1 mark]
When you stir your tea with a metal spoon the handle gets hot because of ________. [1 mark]
When you lot are lying on the beach your skin feels hot because of _______. [ane marking]
radiation
conduction
radiations
Draw energy transfer flow charts for the following: You purchase a cup of hot chocolate and hold information technology in your hands on a cold winter day. [2 marks]
The free energy is transferred from the loving cup to the hands by conduction.
Note:
One of the marks is for choosing the correct direction of the free energy transfer. The 2d mark is for drawing it in the class of a flow nautical chart.
Your parents have a metal hot h2o geyser and they are complaining about the amount of energy needed to keep the h2o hot. What tin y'all recommend your parents could practice to prevent energy loss from the geyser? Explicate your answer. [4 marks]
Metals are good conductors of heat and then the heat from the h2o is transferred out of the geyser. A (shiny foil) insulating coating could exist used to wrap effectually the geyser. The air between the blanket and the geyser is a poor conductor of rut so the heat loss volition be slower.
Explain why the heating element for a kettle is at the bottom and not at the elevation. [three marks]
The heating element is at the bottom because as the element transfers energy to the h2o, the h2o expands and moves upwards and the colder h2o (slower moving particles) will sink to the lesser, forming a convection electric current This bike volition ensure that all the h2o is heated every bit quickly as possible. If the chemical element was at the peak, the water at the bottom would take much longer to boil.
Note:
Learners must mention the term convection current.
Explain why you recollect the h2o boils throughout the kettle pot and non just at the bottom? [2 marks]
The water at the bottom of the pot gets hot and and so moves to the top of the pot because of convection. This allows the cold h2o to sink to the bottom and estrus up. This abiding circulation allows all of the water to heat up and boil.
Explain why you remember take-away coffee is sold in styrofoam cups rather than ceramic cups. [ii marks]
Normal ceramic cups are good conductors of heat and so the free energy from the java is transferred quickly through the loving cup to the surroundings. The styrofoam is a poor usher of estrus and then it does not allow the energy from the coffee to move speedily to the surrounding air, so the java stays warmer for longer.
Explain why you think two sparse blankets tin sometimes exist warmer than one thick blanket. [two marks]
Air is trapped between the two blankets. The air is a very poor conductor of heat and and then it becomes an actress insulating layer which slows down the loss of energy from your body. One blanket cannot trap as much air and so isn't as warm as 2 blankets.
Explain why birds fluff up their feathers to stay warm, specially in wintertime. [2 marks]
Birds fluff up their feathers so that more air gets trapped between the feathers. The air is a poor conductor of rut and so the energy from the birds trunk is not transferred to the surroundings.
Why should you identify an air conditioner at the top of a room, near the ceiling, rather than at the lesser near the floor? [2 marks]
This is because cold air will move downwards, therefore cooling the room, and the hot air will rise and can therefore be removed by the air conditioner at the top of the room, near the ceiling.
Imagine yous desire to build a small enclosure for some chickens on your property. Yous have an outside area for them that is made from barbed wire, and you have fabricated a small within, covered enclosure for them out of bricks and cement which you would like to pigment. Y'all know that it tin can get quite cold in wintertime in your area so you want the firm to be as warm as possible for the chickens. What color paint are you lot going to choose to paint the outside of chicken house? Will information technology be a dark-coloured pigment, such as dark-brown or blackness, or a light-coloured paint, such as white or yellow? Explain your choice. [4 marks]
The best choice to keep the house as warm as possible on the within is a dark-coloured paint. This is because the nighttime colours absorb more radiant heat from the Sun during the twenty-four hour period, than the low-cal colours, which reverberate heat. The nighttime pigment volition blot the heat and it volition exist transferred to the air inside of the house, making it warmer, especially during wintertime.
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