Lesson video

So our lesson question today is where do different colours come from? So last lesson, we looked at how we can see, and now we're going to think about how we can see different colours.

We're going to need our learning from our previous lessons today.

So we're going to be talking about how we see, about reflection and refraction.

So if you've missed out any of the lessons before this, that's okay, but it might be a good idea to go back and watch them when you have time later.

So we've had, this is lesson number five on light so far, and you can find our previous lessons on the Oak National website.

There's also a reason that I have a rainbow on my screen today.

That's because in today's lesson, we are going to be learning about rainbows and hopefully making our own rainbows too.

Today, we are going to need a piece of paper, a pencil, and a colouring pencil.

If you don't have those things, you can pause the video and go and grab them now.

There's something else that we might need towards the end of the lesson.

Now, if you want to have a go at making a rainbow together with me, then you are going to need a transparent glass of water, like this one.

So transparent means you can see through it.

Or maybe an old CD or DVD if you have one around your house.

If you don't have those things, that's okay, you can just watch me do the demonstration, that's absolutely no problem.

You can go and get those things now, if you're feeling super keen or you can wait till we get to that part of the lesson and I'll remind you and give you a chance then too.

Before we begin, let's look at our star words for today.

All of these words we have learned already in our unit.

So we are going to go through the definitions.

If you can remember them already, then you can say them with me.

So absorb, can you remember what absorb means? I'm going to give you a hint with my actions.

Absorb means to take in.

Reflection, can you remember what reflection means? If you know it say it, I'm going to give you a hint with my actions.

Reflection is when light bounces off an object.

Refraction, if you know what refraction means say it to your screen, have a think of those experiment photos I just showed you.

Refraction is when light changes direction as it passes through, how many transparent objects or materials, how many, how many, two.

Well done if you remembered.

And lastly, our most important keyword for this topic is light.

Light, can you remember what light is? If you can say it to your screen.

Light is a type of energy that travels in a straight line from a light source.

Well done if you remembered those.

We're going to start with a recap, this lesson.

Some of that we've already recapped in our star words, we're going to go a bit quickly through this today so we can get into the juicy part of the lesson.

Light, we've just gone through the definition of right.

Through the, ooh, sorry, really tripped up my words there.

Let me try that again.

We've just gone through the definition of light.

So let's read it together, please.

If you know it really well, you could even challenge yourself and close your eyes for this bit.

Light is a type of energy that travels in a straight line from a light source, good job.

What is a light source then? Something that, if you can finish my sentence say it to your screen, something that emits light, good job.

Then we've learned about three types of materials.

So transparent materials like my glass, I'm going to use that term in the lesson, let all of the light pass through them.

Translucent materials let sunlight pass through.

Opaque materials let, remember we looked at these last last lesson, we looked at sunglasses, opaque materials let no light through, well done if you remembered.

We've already looked at the definition for reflection this morning.

See if you can do it with your eyes closed.

If you need a reminder, then you can read it with me, it's on the screen.

When light bounces off an object.

Everybody do the action with me.

Reflection,.

Good job.

And you can see a diagram just like Lana and DJ drew in that work of light from a light source, bouncing off an object and into an eye.

That is how we see.

Can you remember what's the name of the black bit in the eye there, the hole that lets the light through.

Can you remember? If you know it say it to your screen.

It's a pupil, good job.

And our last a bit of recap for today is refraction.

So this is a diagram that shows what's happening in refraction.

If you know the definition, close your eyes and say it with me.

If not, if you need a little reminder, that's okay, we're going to read it out together.

When a light wave changes direction, as it moves from one transparent object to another.

I read that wrong, that's not helpful, is it? Moves from one transparent material to another.

How many materials has it moved through? Two transparent materials.

Okay, now we're going to look at different colours.

Here is a picture of a rainbow.

A rainbow is made up of lots of different colours.

I wonder if you can label all of the colours.

Can you write the numbers one to seven in your margin and write down the colour next to each one.

So for example, I would write number one red, can you figure out what the other colours are? It gets it a little bit harder as you get to the bottom.

And if you've ever learned a song about rainbows, ♪ Red and yellow and.

♪ That might help you.

Okay, pause the video and complete that task for me now, please.

Great, let's see if you were correct.

Red was number one, two was orange, three was yellow, I bet you got all of these right.

Four was green, this is where it gets a little bit trickier.

Five is blue, six is indigo, my turn, indigo, your turn.

And seven is violet, your turn.

So indigo and violet, are kind of bluey-purple colours.

Those might have been the ones that you found a little bit tricky.

Those are the ones that I needed reminding of.

If you made a mistake, great.

That means your brain has just gotten a little bit bigger.

Can you get your coloured pencil, and can you correct your mistake please and write the correct answer.

Check at that spelling of indigo for me, in-di-go.

Brilliant.

This person is Isaac Newton.

And he's a scientist who is famous for a number of his experiments.

But he also discovered something really interesting about white light.

He used a prism, which is a clear, triangular shaped object.

And he found that when he shone light through it, he could split white light into all of the colours of the rainbow.

Going to show you some pictures of somebody trying to recreate Isaac Newton's experiment with a prism.

So here's one picture, you can see the prism is like the triangular transparent thing.

There's a beam of light coming into the prism, and then as it comes out of the prism, you can see it's not, doesn't look like white light anymore, you can see all the colours of the rainbow.

Here's another example.

So again, you can see the light coming in, and then it splits into all of the colours of the rainbow.

Now, the reason this happens is because of refraction, the light is passing through to transparent objects and it's bending.

But not all of the colours of the light bend at the same speed, which is why they split.

So what have he discovered by conducting these experiments is that white light is actually a mixture of all of the colours combined.

So that's what he discovered.

White light is a mixture of all of the colours combined.

I have a question for you.

What did Newton discover about white light? Pause the video and complete that now, please.

Great, let's check our answers.

You may have written something like this.

Newton discovered that you can use a prism to split white light into all the colours of the rainbow.

Well done, if you got that correct, give yourself a big tick.

Okay, next, we're going to look at primary and secondary colours.

Now I have a warning before we do this part of the lesson.

The primary and secondary colours that we're talking about here are the primary and secondary colours of light.

They are different from the primary and secondary colours of paint that you might use in your art lessons.

I know that's really confusing and I'm really sorry, but I don't make the rules, okay? So we just need to remember that the primary and secondary colours in science, and then when we're talking about light are different, okay? So we're just talking about primary and secondary colours of light today.

As white light can be split into a range of colours of light, it's also possible to make light by mixing colours of light together.

So with the prism, we saw white light being split into lots of different colours, but we could also mix all the different colours to make white light.

And that's what you can see here.

You see all these colours have been mixed in the middle that they have turned white, that would be white light.

So by using what we call the primary colours of light, so that's red, blue, and green, and combining them all, we can make white light, okay.

So primary colours are red, blue and green.

What are the primary colours, say it to your screen.

And if we mix them all, we can make white light.

We also, shouldn't,.

Sorry, I'm really tripping up my words today.

It's like my tongue has got two sizes bigger.

We can also talk about secondary colours when we talk about light.

So if we mix two of the primary colours, then we make a secondary colour.

So if we mix all three, we make white light, if we mix just two, we make a secondary colour.

So for example, if we mix green and red, we get yellow.

If we mix green and blue, we get cyan.

Cyan, some people say it like that.

And if we mix red and blue, we get magenta, which looks a bit like pink, but we call it magenta, okay? So those are our secondary colours.

Yellow, cyan, and magenta.

Now we're going to talk about how we see different colours.

We're going to need our star words in this section.

We're going to need our star word reflection.

So remember reflection is when light bounces off an object.

So here, have a look at this picture.

We have a red object.

My light is travelling to that object.

Now it's drawn as all the colours of the rainbow, but we would just see that as white light because white light is a mix of all of those colours, okay? So if we were shining a torch on this red object, this is what would be happening.

We would only see white light, but all of those colours would be in that white light because white light is a mix of all of the colours of the rainbow.

So, our white light is travelling to our object.

When it reaches the object, some of the colours are absorbed, that means taken in, and some of the colours are reflected, that means they bounce off.

So if we look closely at our picture, you can see that actually only one colour is reflected.

Which is the one colour that is bouncing off the object? It's red.

All of the other colours are absorbed.

So, who's noticed the pattern there.

What colour is the object? What colour is the light bouncing off? They're both red.

That's the reason that we see the object as red, because only the red light is reflected into our eyes.

What do you think would happen then if the object was yellow.

Which colours would be absorbed and which would be reflected? Well, if the object was yellow, then all of the colours apart from yellow would be absorbed, and then the yellow would be reflected into our eyes, which is why we would see it as yellow.

Here, we have a white object.

Have a close look at the picture and see if you can figure out what is happening this time.

So white objects reflect all the colours of white light.

And that's why they appear white because white is a mix of all the colours, okay? So white objects reflect all of the colours so they reflect white light.

What about this black object, what's happening this time? Black objects absorb all of the colours and they don't reflect any of the colours of light back, which is why they look dark.

Okay, time for some questions.

These are your questions.

And I've put the pictures up on the side, just in case you need a little memory jog.

Okay, I'm going to make it full screen so that you can see it really clearly, and I'm just going to read them to you before you begin.

What happens to white light when it hits a red object? What happens to white light when it hits a green object? What happens to white light when it hits a white object? And what happens to white light when it hits a black object.

Can you use the word reflect and absorb in all of your answers please.

Pause the video and answer the questions for me now.

Great, let's see if you got these correct.

So number one, red light is reflected and the other colours are absorbed.

So that's whats happens, that's what happens when it hits, the white light hits a red object.

In number two, when white light hits a green object, green light is reflected and the other colours are absorbed.

In number three, when white light hits a white object, all of the colours of light are reflected equally.

And then number four, when it hits a black object, all the colours of light are absorbed.

Well done if you got those correct.

If you need a moment to correct or add to your answers, just pause the video and do that for me now, please.

Okay, now we are going to learn how a rainbow is made.

Have a look at this picture.

That blue circle is a raindrop.

So rainbows appear in our sky, right? In our sky, we also have clouds that are condensed water.

Okay, they're filled with raindrops.

They're full of little droplets of water.

So that blue circle represents one of those rain droplets.

Now the lines show the light from the sun coming into the rain droplet.

Three things happen that cause a rainbow.

So we're going to go through each one.

The first one is that light from the sun comes into the rain droplet and it changes direction.

So that's where refraction is occurring.

Light from the sun comes into the rain droplet and it changes direction.

The second thing that happens is that the colours of light start to spread out before they all bounce back off the rain droplet.

So when they reach the back of the rain droplet, reflection takes place.

Reflection is when light bounces off.

Then the colours spread even further as they leave the rain drop and change direction again.

So refraction is taking place again, okay? So a ray of light comes into the rain drop, bounces off the rain drop, and then comes out again.

When it comes into the rain drop, it changes direction, so refraction is occurring.

Then it bounces off the raindrop, that's reflection, and then it leaves the raindrop and changes direction again, and that's refraction occurring.

Okay, so it goes, refraction, reflection, refraction.

Say it with me.

Refraction, reflection, refraction, okay? Now, this happens, when this happens, it doesn't just happen in one raindrop.

It happens in millions of raindrops in the air at the same time and a rainbow is created.

Which is why rainbows are created when sunshine meets rain.

So we don't always see rainbows in our sky, it needs to be a particular type of weather when we have sunshine and rain.

Take a mental image of that picture in your brain because I'm going to see if you can remember what happens.

Can you add the correct labels to this diagram please? Great, we're going to check if you are correct.

A, was refraction, B, was reflection, and C, was refraction.

If you would like to challenge yourself, then I would love to see you writing a sentence to explain what happens at A, B and C.

Pause the video and complete that now.

Great, so if you had a go at doing that, then you might have written something like, at A, the light ray enters the rain drop and changes direction, so refraction is taking place.

For B, you might have written something like, the light ray reflects off the back of the rain drop, reflection is taking place.

And then for C, you might have written something like, the light exits the raindrop and changes direction, refraction is taking place.

And through all those steps, the white light is starting to spread out into its different colours.

We've learned that inside a raindrop, we need reflection and refraction to make a rainbow.

And now I'm going to teach you a couple of ways to see if you can use reflection and refraction to make your own rainbows.

I wanted to show you a demonstration of this, but you'll see when I show you the instructions, that actually it would be quite hard for me to film myself doing it because for these, you often need a darker room in order to do it.

So you actually wouldn't be able to see what I was doing.

So instead, I'm going to show you a picture, and I'm going to read the instructions with you, and then at the end of this lesson, you can try for yourself.

There are two methods, so you can see which one you maybe have the equipment for, and have a go and see if you can make your rainbow.

So here is our first method.

So for this method, you will need a mirror and a glass of water, like a small mirror.

You also need to be near a window which has natural sunlight for this method.

So let's go through the instructions.

Step one is to fill your glass with water.

So you can see in the picture that the glass is filled with water.

Step two is to put the mirror into the water, inside the glass at an angle.

So it's not going straight in, it's at an angle.

Step three is to position the glass so that sunlight shines directly at the mirror.

So you want your mirror to be facing your window so that sunlight is directly at it.

Then you need to look for the reflection on the wall.

It will be easier to find this if your room is dark, and if there's not other things on the walls.

And you're going to need to adjust in step five, the angle of your mirror until you see the rainbow on the wall.

So that might mean you need to rotate your glass, you need to change the angle of the mirror and keep fiddling it with that until you see the rainbow on the wall.

It can take awhile to get it right, 'cause you need to get the angle just right.

But see if you can persevere and get it to work.

If that doesn't work, or if you don't have a mirror, you could try the second method.

So in the second method, you need two pieces of white paper or card, you need a glass of water again, you're going to need some scissors in order to cut a slit in your paper, so make sure you check with your parent or carer before you do this, please.

And you're going to need a light source.

A torch would be good, and a torch that has a bright white light is going to work much better than a torch with like a yellowy light, okay? Because remember it's white light that we're trying to split into all the colours.

You might be able to use the torch on an iPhone, if you don't have your own torch or a torch on a phone.

So step one is to say, you need to fill your glass with water.

Step two, cut a rectangle in the middle of one of your pieces of paper, try and keep it as narrow as possible.

So you might need to fold the paper in half to do this.

Then set your paper up as shown in the picture.

So you have one piece of paper on the table, or the surface that you're using, then you have your glass in the middle, and then you have one piece of paper with a slit in it, leaning up on the glass.

Next, you're going to want to switch the lights off.

This experiment, this version is best done in a dark room, pitch black, if you can.

And then you're going to switch your torch on and point it directly at that slit in the piece of paper.

So you're going to point your torch directly through this slit here.

Start from the glass, so start with your torch pressed right up against the glass and then slowly move the torch further and further from the glass until you see a rainbow on the paper on the other side.

Again, this can be a bit fiddly.

So have a go and see if you can get it to work.

Well done for all of your hard work today.

I hope you enjoyed the lesson.

Just before we go, and you do your post-lesson quiz, let's have a quick recap of our key words.

Absorb means to take something in.

Reflection is when light bounces off an object, refraction is when light changes direction, as it passes through two transparent materials.

And light is a type of energy that travels in a straight line from the light source.

If you would like to send me a picture of your work, then I would love to see it.

If you're going to send in your work, it needs to be sent in please by your parent or your carer.

And they can share your work on Twitter with the #LearnwithOak, or tagging Oak National, and then I will be able to see it.

I have had so much fun with you in today's lesson, and I am already excited for our next lesson, which will be all about the different ways we can use light.

And there will be lots of chances for us to do some hands on science.

I hope you have a brilliant rest of your day and I will see you soon.

Goodbye.