Hello and welcome to this lesson which is a practical about absorbing infrared radiation.

This is from the unit called Electromagnetic Waves and my name's Mr. Norris.

So this lesson is a great opportunity for you to show off how far you've come with your scientific and investigative and experimental skills and how well you can actually set up an experiment and collect valid data.

So let's get going.

Here's the outcome of today's lesson.

By the end of the lesson, you'll have shown that you can investigate how the intensity of black ink affects the infrared radiation absorbed by a surface.

Here are some key words that will come up this lesson: absorption, infrared radiation, electromagnettic wave, frequency and control variable.

A definition for each keyword is given here.

Pause the video now if it would be helpful to review these definitions at this point, but for each keyword will be explained as it comes up in the lesson.

This lesson has two sections.

In the first section is where you will investigate the absorption of infrared.

And in the second section, we'll look at your results and draw some conclusions.

Let's get going with the first section.

So a hot object can warm your hand without contact, without touching, and that's because your hand would be absorbing the invisible infrared radiation that's emitted from a hot object like that iron in the picture.

And what is infrared radiation again? Well, it's just electromagnetic waves.

So same thing as what light is, but with frequencies in a range just lower than the frequency of red light.

So here is a frequency scale showing a huge range of possible frequencies that electromagnetic waves can have with the visible frequencies labelled.

And you can see the range of frequencies that correspond to infrared radiation.

So infrared radiation is just electromagnetic waves that you can't see because the frequency is just lower than the frequency of visible lights.

Let's do a check now on your understanding of infrared.

Which of the following statements are correct? Now the wave equation, wave speed equals frequency times wavelength, which is true for all waves, that's just there to help you work out which of the following statements are correct.

So pause the video now and have a look at A, B, C, or D, which are correct? Off you go.

Right, I'll give you some feedback now.

So statement A is correct 'cause infrared radiation is just a range of frequencies of electromagnetic wave.

B is not correct 'cause infrared radiation has a lower frequency than visible light.

For statement C, all kinds of electromagnetic radiation have the same speed in air, so C is false.

And D, infrared radiation has a longer wavelength than visible light, that's true.

And you could have worked that out from the wave equation because if infrared radiation has a lower frequency than visible light, but the same speed in air as all the other electromagnetic waves, if the frequency is lower, the wavelength must be a bigger number.

So a longer wavelength.

So the frequency times wavelength gives the same wave speed.

Well done if you've got that right.

So all objects are actually constantly emitting or radiating electromagnetic waves into their surroundings.

Now if an object is glowing bright, then it's emitting visible electromagnetic waves.

But it turns out even objects that aren't glowing are also constantly emitting electromagnetic waves into their surroundings, just the invisible kinds.

So the range of frequencies of electromagnetic wave that an object emits and the intensity of each frequency, that all depends on an object's temperature.

So room temperatures and below, objects don't give out visible light because if they did, then everything we look at would be glowing and they don't give out any higher frequencies either.

So room temperatures and below, objects mainly emit infrared radiation.

So it's lower frequencies for visible lights.

But as the temperature of an object increases, the intensity of every frequency emitted also increases.

And the range of frequencies emitted also increases to include higher and higher frequencies.

So the hotter an object is, the more infrared it emits in a given time for both of those reasons.

The higher the temperature, the higher the intensity of the frequencies emitted and also the more frequencies emitted 'cause more higher frequencies are emitted too, the hotter temperatures.

So we just said that as the temperature of an object increases, the range of frequencies emitted increases to include higher and higher frequencies.

And at around 600 degrees C, and it's the same temperature for every object, objects start to emit visible frequencies of electromagnetic wave as well as the infrared frequencies that they were already emitting at lower temperatures.

As objects get to around 600 degrees C, they start to emit red light first because that's the lowest frequency of visible light.

So objects become red hot at around 600 degrees C and above.

And the higher the temperature, the higher the frequencies of visible light that can be emitted.

So as the temperature increases, objects will start to emit orange light and yellow light as well.

If the temperature continues to increase, an object can emit all the frequencies of visible light.

And then, it will look white.

And then, an object is white hot.

That's like the bulb filament in the fourth picture, which is about 3000 degrees C.

It's emitting all frequencies of visible light.

So it's glowing white, it looks white, it's white hot.

White hot is hotter than red hot.

Now for objects in that range of temperatures between about 600 degrees C and 4,000 degrees C, which are glowing, they actually still transfer much more energy via the infrared radiation that they're still emitting rather than the visible light that they've started to emit because of their high temperatures.

Now, objects like the sun, that's not true.

For the sun air, the surface of the sun is around 6,000 degrees C.

So something that's as hot as that might be transferring just as much energy via infrared as via visible frequencies and above.

For example, the sun emit some ultraviolet as well because it's so much hotter.

So this means that for most glowing objects on earth, which are gonna be between about 600 degrees C and 4,000 degrees C, their heating effect is actually mainly caused by the infrared radiation that they're still giving out rather than the visible light they've started to give out because of their temperature.

That's a point that's probably worth repeating just to emphasise it.

For most glowing objects on earth that are in that temperature range, their heating effect is caused by the infrared they're giving out, not the visible light.

Let's do a check on what we've just said.

So a piece of card is attached to a thermometer.

This is very similar to the experiment you're gonna do in this lesson.

The thermometer bulb is touching the card.

So the thermometer is measured the temperature of the card.

The card is placed close to a glowing heater or lamp, which is at 3,000 degrees C.

The temperature of the card rises.

Which option most accurately describes what the card absorbs that is the main cause of this temperature rise? Choose from A, B, C, or D and hopefully this is a really easy one.

Okay, I'll give you some feedback now.

The card absorbs infrared radiation from the lamp.

I mean you can say that the card is absorbing heat from the lamp, but that's not as specific about what the bulb is actually emitting.

Heat just means energy and lots of things can transfer energy.

What's transferring the energy to the card in this case? Infrared radiation, that's the specific name for what's transferring the energy to the card.

Heat radiation is kind of a vague term and it's not the visible light, it's the infrared radiation from the lamp.

Well done if you got that, I'm sure you did.

So let's now talk about the experiment that you're gonna do.

You are going to investigate how the intensity of black ink affects how well a surface absorbs infrared radiation.

So what you'll need to do to do this is you'll need to cut out each row of the table separately.

And then, each side of the card can be folded behind on the lines and the percentage label is then glued on top of the X.

And that's gonna make a flat sleeve of card that can be fitted over a thermometer bulb, one flat sleeve of card for each shade of grey if you cut out every row of the table and do that for every row of the table.

And the shade of grey that will have achieved the greatest temperature rise in a fixed amount of time will have absorbed more infrared radiation.

Have a look at Sofia's prediction here.

Sofia's saying black surfaces absorb all frequencies of visible light and that's correct.

And white surfaces reflects all frequencies of visible light.

Well, that's correct, that's why they look white.

So Sofia's saying she thinks it will be the same for infrared.

The more black ink, the more infrared will be absorbed.

So she's predicting that black surfaces are gonna absorb all frequencies of infrared better than whiter surfaces because black surfaces are gonna absorb all frequencies of infrared just like they absorb all frequencies of visible light.

That's her prediction.

But look what Lucas suggests.

Lucas is saying infrared doesn't have to behave in exactly the same way of as visible light.

He's saying black ink might reflect infrared even though it absorbs visible light.

'Cause remember, each different frequency range of electromagnetic wave can interact differently with different materials.

So what do you think? Can you think of any reasons to back up a prediction? Pause the video now and have a bit of a think about what you think is gonna happen in this experiment.

Is it the darker intensities of black ink or the lighter intensities or somewhere in the middle that's gonna absorb most infrared radiation in this experiment? Let's talk a bit about the method you're gonna use now.

So to find out how the intensity of black ink affects the amount of infrared absorbed, all the other variables that might affect the absorption of infrared need to be kept the same.

And these are called the control variables in an experiment, of course.

And otherwise, higher or lower temperature rises could be caused by other factors that you are allowed to change rather than a different intensity of black ink.

That's why everything, all the other factors, all the control variables have got to be kept the same.

So only changing the intensity of black ink and keeping all of the variables constant, that's gonna give you valid results.

Results that will actually help you answer the question of does the intensity of black ink affect the amount of radiation absorbed? So you are gonna investigate how the intensity of black ink affects the amount of infrared radiation absorbed in a set time.

Which of the following should be control variables for your investigation? Choose from this list and tick the ones you think should be control variables that you need to keep the same in your experiment so they don't affect your results.

Pause the video now and decide from this list.

Okay, I'll go through some answers now.

Now A, the intensity of black ink, that's your independent variable.

That's what you are gonna change each time.

So that's not control variable.

B, the temperature rise in a set time, that is your dependent variable.

That's is what you are gonna see if it changes when you change your intensity of black ink.

So that's not a control variable, that's something you just let changes and you're gonna monitor and see if it changes when you change the intensity of black ink.

Now all the others are actually control variables.

You've gotta keep the power of the heater the same 'cause using a more powerful heater might heat the card a bit more.

You've gotta use the same type of ink 'cause different types of ink might interact with infrared differently.

And it wouldn't be fair if you change the type of ink halfway through the experiment.

The area of the card should be the same, 'cause a greater area exposed to infrared, it's gonna absorb more infrared potentially and could show a greater temperature rise.

The angle of the card to the heater.

That should be the same because objects will absorb more infrared radiation when they're faced onto the heater compared to if they're an angle, they'll present kind of a smaller, frontal area to the heater.

The distance between the card and the heater, that's gotta be the same 'cause if a card was closer, then the intensity of infrared hitting it might be greater.

And the starting temperature of the card, that should ideally be as close as to the same as you can get it in this experiment every time.

Because if a card started hotter, that might affect how much infrared radiation it can then absorb at different temperatures.

So we should keep it the same.

Well done if you identified all of those.

Now, when you do this experiment, you will need to design a results table to record your results in.

Remember to put units only in the column headings.

And for each intensity of black ink that you're gonna test, you'll need to record the starting temperature and the final temperature 'cause you always record the raw data and you'll then calculate the temperature rise by finding the difference between the measurements you actually make of the starting temperature and final temperature.

We want the temperature rise, so we need the difference between final temperature and starting temperature.

And leave space for repeat measurements and mean results if you've got time to collect them.

If you repeat each measurement, then that can help you check for mistakes that cause anomalous results.

It also allows you to see if your results are repeatable, which is a sign of reliable data.

And calculating a mean would reduce the effect of any random errors in the data you collected.

So that would be the benefit of repeating results if you've got time to do so.

Okay, let's do a quick check before you now crack on with the experiment.

Which of the statements below would be a source of random error in the experiment, a source of systematic error in the experiment, and a safety consideration? So look at A, B, and C and match them up to one, two, and three.

Pause the video now and do that.

Okay, let's see how you got on.

Statement B is a source of random error in the experiment because the slightly different angle or slightly different distance could be different each time.

Sometimes too big, sometimes too small.

So you can't predict the level of the error.

It's a random level of error.

So that's why it goes with statement number one.

Now, a source of systematic error in experiment would be C because if C happens, that would suggest that every temperature measurement you make could be out by four degrees.

So that's an error that's the same every time.

So it's called a systematic error.

And remember that they are the only two kinds of error.

All errors are either random errors or systematic errors.

So if you ever get a question, which is what type of error is this, it's probably either gonna be a random error or systematic error.

That leaves a safety consideration of statement A, which hopefully was pretty obvious.

Well done if you got those right.

Okay, so it's time for you to do this task now.

Investigate how the intensity of black ink affects the absorption of infrared from a hot lamp or a heater.

You should do a test run to help choose a sensible time over which to record the temperature rise.

You should trial the lowest and highest intensities of black in first to then check your chosen time, gives a good range of results.

You should ensure the control variables are kept the same throughout, like we talked about.

You should record all the results collected.

And if time allows, then take some repeat measurements and calculate mean results.

If you don't have access to equipment, have a look at the example results on the feedback slide.

So I'll see you when you've had a good go at collecting that data.

Well done for your effort in that experiment.

Now hopefully your results might look something similar to this and no repeats were taken in this example data.

Each card was five centimetres from a 50-watt heater in this experiment for two minutes, which was the time chosen.

So that takes us to the second section of the lesson where we're gonna draw some conclusions from data.

So a conclusion states what you found out in an experiment and how you know.

So here are the example results.

Izzy collected these results, this is her data.

So complete the conclusion that Izzy can draw from her results.

Pause the video now.

Make sure you can fill it in the blanks.

Right, I'll give you some feedback on this.

Now Izzy's results clearly show that the higher intensity of black ink, so moving from zero to a hundred, the more infrared radiation was absorbed in two minutes, causing a greater temperature change or higher temperature rise.

Well done if you got that.

Now, variables, the things that can change in an experiment such as the independent variable, which is the thing that you change to see what effect it has, and the dependent variable, which is the thing that you monitor to see if it changes in an experiment.

Variables can be categoric or continuous.

Categoric variables have distinct, separate values.

So shape is a categoric variable because a shape is either a circle, a triangle, or a square.

Type of tree is a categoric variable because a tree is either an oak, an ash, a pine, or a palm.

So categoric variables come in categories.

The name gives it away really, separate categories.

Whereas continuous variables can take any value on a numerical scale.

So that's things like height and volume.

So here at Izzy's results again, just showing the temperature change this time, not her raw data.

So should Izzy draw a bar chart or a line graph? You need to decide the answer to that question, but also fill in the gaps to justify your answer.

Pause the video now and see if you can do that.

Okay, I'll give you some feedback.

So hopefully you realise that Izzy should draw a line graph, but what's the correct reason why Izzy should draw a line graph, not a bar chart? The correct reason is because her independent variable, the thing she changed and is gonna put on her X axis of the graph, the intensity of black ink, that is continuous.

It's a continuous scale of numbers.

Intensity of black ink in theory could have any value from zero to a hundred on a continuous scale.

So her x axis needs to be a continuous scale of numbers, not divided into separate labels for separate categories for separate bars.

Well done if you got that right.

Okay, so that takes us to the final task of this lesson.

There's two parts to this task.

First part is to draw a line graph of Izzy's results.

We've explained why it needs to be a line graph.

You should do that on graph paper and do it using a pencil, a ruler, nice and neat.

And then part two of this task is a question based on the results of this experiment.

Houses in hot countries are often painted white.

Have a look at that picture.

So part A, use Izzy's results to suggest why painting a house white in a hot country might help to keep the houses cool.

So piece of writing for part A.

And part B, suggest a possible problem with applying Izzy's results directly to that context.

Pause the video now and have a good go at all parts of that task.

Okay, I'm gonna give you some feedback now.

So your graph should look something like this and should have the features that I've listed on the left hand side of this slide.

A graph should have a meaningful graph title.

I've gone for a graph showing how the intensity of black ink affects how well a surface absorbs infrared radiation.

You could have gone for something like a graph showing the temperature rise for different intensities of black ink absorbing infrared radiation, as long as it's something along those lines that describes what the graph shows.

Now each axis should have a title and a unit.

That's the intensity of black ink with the percentage 'cause those are percentages and the temperature rise in two minutes with degrees C in brackets because those are temperatures.

We need the units and brackets by the axis titles.

The x axis scale going up in even amounts: 0, 20, 40, 60, 80, 100.

And the y axis scale, again going up in even amounts: 0, 5, 10, 15, 20 in this case for Izzy's results.

You need to make sure the points were plotted accurately and there should be a suitable line of best fit.

Now for Izzy's data, I've drawn a straight line of best fit because that's just about justifiable.

We've got two points above the line and one point below the line and all the other points are pretty much on the line.

So a straight line of best fit is justifiable just about for this data, but you might have drawn a curved line of best fit like that and that's justifiable as well because then you've got all but one of the points fitting really nicely to that curve with one potentially anomalous result.

So well done if your graph looks something like what I just showed you.

Here's some feedback from part two of the task.

We're gonna have to say what Izzy's results show.

And then, why might that mean painting a house white in a hot country could keep the houses cool.

So here's an example answer, make sure yours is along these lines and make any improvements that you need to.

Izzy's results show that the lower the intensity of black ink, the lower the temperature rise in a set time due to absorbing infrared radiation.

And that suggests that white surfaces are gonna be worse absorbers of infrared than darker surfaces.

So if the walls of the house are painted white, they might absorb less of the sun's infrared, keeping the house cooler.

Hopefully that was fairly straightforward.

And here's part B, suggest a possible problem though with applying Izzy's results directly to this context.

Well, I think there's two that I thought of.

The first one is that infrared might interact differently with paint on a house wall than with ink on paper, which is what we did in the experiment.

So you might not actually be able to apply Izzy's results to this situation.

And the second problem could be that the sun's radiation might contain different frequencies of infrared than the heater that was used in this experiment.

So that also might mean the results couldn't be applied to this situation successfully as well.

Well done if your answers were along those lines.

Pause the video and make any improvements to your work that will help your learning.

Here's a summary of the lesson.

All objects emit infrared radiation, which can be absorbed by other objects causing heating effect.

The range of frequencies emitted and their intensities depend on an object's temperature.

Infrared consists of electromagnetic waves with frequencies and a range just lower than that for red light.

Darker surfaces are usually better absorbers of infrared radiation than lighter surfaces.

And control variables are variables that are kept the same during an experiment.

So only the independent variable that you're investigating can affect the results.