Lesson video

Hi, everybody.

I'm really excited to be back for another science lesson.

Well done for all your hard work in our last lesson and a big thank you to all of you who sent me your photos on Twitter.

That was really great to see.

We're going to continue this lesson with our unit of light.

And today we are going to be learning all about reflection.

So this is our lesson question for today.

We are going to answer the question, what is reflection and how can we use it? So before we begin, let's have a look at the equipment that you will need for this lesson.

So today you will need an exercise book or a piece of paper, a pencil to write with, a colouring pencil if you would like to mark your work in a different colour as we go, and a ruler so that when we're drawing tables, you can draw really straight, neat lines.

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

Let's take a look at what we are going to learn this lesson.

This is going to be the structure of our lesson today.

So we are going to start with our star words.

That's our key vocabulary.

Then we're going to do some recap of the learning that we did last lesson to see what we can remember.

Then we're going to look at two types of materials: we're going to look at reflective materials and non-reflective materials.

Then we're going to look at two types of reflection: specular reflection, which is a word I really like to say, and diffuse reflection.

And lastly, we are going to learn the law of reflection, which is a rule about reflection that can't be broken.

So let's take a look at our star words.

Remember, the star words that are underlined are the ones that we will define at the beginning of the lesson before we do our learning.

And then the ones that aren't underlined, we will learn as we go through in the lesson.

And then we'll come back to all of them at the end of the lesson.

So our first star word today is "absorb." "Absorb" means to take in.

So an example of when we might use that is if we were talking about a piece of kitchen roll or a piece of tissue paper absorbing water.

That means that it takes in the water.

Our next star word is "reflect." We learnt about reflection last lesson.

When light is reflected, it means it bounces off an object.

And we did this action to help us remember last lesson.

So have a go at doing the action and saying, "Reflect" with me now to help it stick in our brains.

"Reflect" means to bounce off.

And then our last star word we're going to look at this morning is "angle." This might be some vocabulary that you are familiar with from your math lessons.

And I've put a picture next to the star word to help us remember what it means.

An angle is the amount of turn between two lines around that common point, which we call a "vertex." So where the two lines meet is our vertex.

And we measured the amount of turn between two lines.

That piece of math vocabulary is going to be important in today's lesson because we're going to be looking at angles when light is reflected.

So let's start with the recap part of our lesson.

I'm excited to see how much you can remember.

Well done if you had a go during the pre-lesson quiz.

The answers to these questions will come up when we go through what we did last lesson.

If you have forgotten anything or you got any of the answers wrong in the quiz, that's fine.

That's why we're going to recap it now.

And the more times we recap it, the easier it will be to remember next time you do your quiz.

So the first thing we learned about last time was light and light sources.

I'm going to show you the definitions for these in a second, but if you can remember them, then when I say the word, I want you to say it out loud to your screen.

When we say things out loud, it can help us to learn them.

Say, can you remember what light is? Say it to your screen.

Great.

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

Well done if you remembered.

Can you remember what a light source is? There are some examples in the pictures on your screen.

So the sun is a light source, and so is a torch.

If you can remember what a light source is, say it to your screen.

A light source is an object that emits light.

We also learned about three different types of materials.

And the reason that they are different is because of the amount of light that they let pass through them.

So the first material we learned about were.

We also learned about three different types of material: transparent, translucent, and opaque materials.

And the reason that they are different is because of the amount of light that they let through.

So we learned that transparent materials let all of the light to pass through them, just like in the picture on the screen.

Translucent materials let some of the light to pass through them, and opaque materials no light pass through them.

We started to look at reflection last week and we learned the definition.

If you can remember what reflection is, you might remember it from our stars words at the beginning.

Say it to your screen now.

Reflection is when light bounces off an object.

Well done if you remembered and well done if you remembered to do the action as well.

And you can see this diagram on the screen shows that light is being emitted from a light source, travelling in a straight line to an object.

Then when it reaches the object, so the apple in this case, it's reflected, it bounces off the object, and into this person's eye, which is what enables them to see.

we're going to learn lots more about reflection today.

We also looked at darkness and shadows.

And we did a great investigation on the kinds of shadows that can be made with materials.

If you remember the definition for the word "dark," say it to your screen.

Dark is the absence of light.

Well done if you got that correct.

We also learned about shadows.

If you can remember what a shadow is or how it's formed, say it to your screen.

A shadow is an area of darkness created when an object blocks light.

So you can see in this picture that there is a shadow of that tree.

And it's in a tree shape because the tree is blocking the light.

Light can only travel in a straight line.

So it can't go around the tree.

It can't go through the tree because the tree is an opaque object.

And so it's blocked by the tree, and that creates an area of darkness behind the tree which we call a shadow.

Now let's start the learning, the new lighting for today's lesson.

We're going to look at two types of material today: reflective materials and non-reflective materials.

So, so far, we've learned that when light hits an object, it can pass through it, like in transparent materials, or it can be absorbed, that means taken in, like in opaque materials, but like can also be reflected from an object.

There is some light reflected off every object because that's the light that is reflected into our eyes and allows us to see it.

But the type of material depends on how much light is reflected.

So reflective materials are materials that reflect light well, and non-reflective do not reflect light so well.

We're going to look at some images now to help explain that.

So the kinds of materials that are non-reflective are ones that have dull or dark surfaces.

And this is a diagram that shows what happens when the light reaches a non-reflective material.

A small amount of it reflects off, which allows us to see it, so that's represented by the grey line, but most of it is absorbed by the material.

And remember, "absorbed" means to take in.

In contrast, reflective materials are often smooth and shiny surfaces.

And when light hits a reflective material, almost all of it reflects off.

So you can see the difference in the arrows here.

A dull and dark material absorbs most of the light.

So we just have a small arrow reflecting off.

But in a smooth and shiny surface, all of the light is reflected off.

And so we have our big, thick, red arrow showing that.

Some examples of dull and dark non-reflective materials might be things like cardboard or fabric.

And some examples of smooth and shiny surfaces that are reflective are things like mirrors or maybe metal cutlery that you might have and shiny objects or fabric like tinfoil.

So let's recap those definitions.

Ar reflective material reflects light well.

Most of the light that hits the surface bounces off.

A non-reflective material does not reflect light well.

Some of the light bounces off the object, but most of the light is absorbed.

Let's take a look now at some example materials and see if we can decide which ones are reflective and which ones are non-reflective.

So this calls for my science box.

Let me go and grab it, and we can see what's inside today.

So, inside our science box today, we have a metal spoon, we have a box that looks like it's made out of a mirrored material, we have a plastic bag, we have some filter paper, we have a piece of kitchen roll, we have some cardboard, and we have a piece of kitchen roll.

So let's think about each of these materials in a bit more detail.

I'm going to leave our definitions of reflective and non-reflective materials up on the side, so we can hold them in mind when we're observing each material.

So let's start with the kitchen roll.

This material is non-reflective.

There is not very much light that is bouncing off this material.

There's enough for us to see, but not a lot.

And one of the ways we can remember this is 'cause this material is dull and it's not shiny.

What then do you think the filter paper will be? If you know, tell your screen.

Is it reflective or non-reflective? Great.

This material is non-reflective.

Most of the light is absorbed.

What do you think this material is Remember, we learned that reflective materials are often shiny.

So this material, this tinfoil, is reflective.

It reflects light well, and most of the light that hits the surface bounces off.

What do you think this material is? If you know, tell it to your screen.

Correct.

This material is reflective.

It's shiny, they can see, and it reflects light well.

Most of the light that hits the surface bounces off.

What do you think about this material? Now, this clear plastic is one that we looked at last week.

So we've already learned that we could describe this material as transparent.

That means light passes through it, which is why you can see my face through it.

But could we also describe this material as reflective? I think, yes, we can.

You can see that it's shiny.

So that means that some of the light is passing through this material, which is why it's transparent, but there is also some light that's reflecting off it.

That means it's a reflective material as well, which is why it looks shiny.

What about this cardboard? Reflective or non-reflective? Say it to your screen.

Great.

This material is non-reflective.

Some of the light bounces off, but most of it is absorbed.

What about this object? It's made from a mirrored material.

Reflective or non-reflective? Say it to your screen.

Great.

This material is reflective.

It's very reflective.

In fact, it's so reflective that I can see a really clear image of myself in the mirror.

So the next thing we are going to do is we are going to draw a table in our exercise books or on a piece of paper.

So I would like you please to draw a table that looks like this with your ruler.

And you need to have two columns.

And the headings of your columns should say "Reflective materials" and "Non-reflective materials." So you can pause the video and complete the task now.

Great.

Once your table is ready, let's look at how we are going to use it.

You have six different labels here and images, and you need to sort them into two categories: either your reflective or your non-reflective column of your table.

You don't need to write the whole sentence out or draw the picture, although you can if you want.

A quicker way of doing it would just be to put the letter in each column.

So for example, if you think dull and dark materials should go in the non-reflective column, then you just need to write an A in the non-reflective column because that is what that label is attached to.

You can now pause the video and complete the task on the screen.

Great.

When you're finished, let's check our answers.

This is what you should have got.

So the labels A, C, and D should be in your non-reflective materials column.

So dull and dark materials.

The diagram that shows absorption and the definition that says, "Do not reflect light well.

Some light bounces off the object, but most of the light is absorbed." And then in your reflective column, you should have had smooth, shiny materials, the diagram that shows reflection, so E, and F.

Reflects light well.

Most of the light that hits the surface bounces off.

Okay.

So remember, non-reflective materials absorb most of the light.

Do the action with me.

Absorb.

And reflective materials reflect most of the light.

Do the action with me.

Great.

Now, if you would like to, you can have a go back adding some information to your table.

I wonder if you can go on a materials hunt around your house and see if you can find any materials, like the ones in my science book, that you can sort into your table.

So can you find any reflective materials, like my shiny spoon? Can you find any non-reflective, like my dull cardboard? If you'd like to have a go at that, then pause the video and go on your materials hunt now.

Great.

When you're ready, we will go on to the next part of our lesson.

The next thing we are going to learn about is specular and diffuse reflection.

So we have already learned that reflection happens when light bounces off an object, but the light can bounce off the object in different ways.

The first way that we're going to learn about is specular reflection.

Specular reflection, because when light hits a smooth object.

So you can see in this diagram here, the light rays, which are shown by the arrows, so there's a green one, a blue one, and a red one, they are all travelling in a straight line and hitting a smooth object.

Diffuse reflection, because light is reflected off an object that is rough or bumpy or not smooth.

So you can see how those two pictures occur.

So when diffuse reflection occurs, the light hits the object, but because the surface is not smooth, the light rays reflect in different directions.

So you can see the green light ray is reflecting off in this direction, but the red light ray reflecting in that one, and the blue is reflecting in that one.

So the lights scatters.

Let's have a look at some pictures that show what's going on in those diagrams. So this is a picture that shows specular reflection.

So you can see that there is a light coming in from the sun, and it's hitting a very smooth surface.

So there is a mirror that the light is hitting a very smooth surface.

Because the surface is very flat, all the light bounces off in the same direction.

This means that specular reflection takes place.

And this is what happens when light bounces off a mirror, like in this picture, or something like the surface of a puddle.

Here's a picture that shows what happens when diffuse reflection takes place.

So when the surface is not smooth, diffuse reflection takes place.

Because the surface is rough, the light bounces off lots of different directions.

And this is what happens when light bounces off most surfaces, such as walls, tables, and paper.

So even though they might feel or look smooth to us, when you zoom in on the surfaces, if you were to use a magnifying glass or a microscope, you would see that they have lots of little bumps in them.

And those bumps are what cause diffuse reflection to take place.

So here's a look at the two photos next to each other, so you can see a comparison.

You've got diffuse reflection on the left when the light is scattering in lots of directions, and then you've got specular reflection where you can see the rays reflecting in the same direction.

Let's recap those definitions.

So say them with me.

Specular reflection.

When light bounces in the same direction.

And I think we can do this action to help us remember.

And diffuse reflection is when light bounces in many different directions.

Okay, so now I'm showing different directions.

It's really important to understand things like specular and diffuse reflection because it can help us to choose the correct materials when we're building.

So an example of this is when building solar panels.

So solar panels help us to convert light energy from the sun into electrical energy that we can use in our homes to power our lights and our computers and electricity switches in our house.

Solar panels perform much better when they are specular.

So if there's diffuse reflection going on inside a solar panel, it doesn't work very well.

But if the reflection is specular, then they work much better.

So that's why it's important to understand things like this.

I have a really sticky way of remembering the difference between specular and diffuse reflection.

Specular reflection begins with an S and so does same direction and smooth surfaces.

And diffuse reflection begins with a D, and so does different directions.

So that will help us to remember our definitions.

Can you have a go now, please, at answering these questions? What is specular reflection? What is diffuse reflection? What kind of surfaces cause specular reflection? And give an example of a surface that causes specular reflection.

Remember my sticky way of remembering.

And you can now pause the video and complete those questions on your piece of paper.

Great.

When you're finished, we're going to have a look at the last part of our lesson.

We are going to have a look at the law of reflection.

Now, in order to explain this, I'm going to show you a drawing that I'm going to make and I'm going to explain as I do it.

So I'm just going to share that with you now.

So this is a diagram that we should be familiar with.

So this is a diagram showing how light is reflected from a mirror.

So down here, this is my mirror.

And then this is my light ray that's travelling from my light source, it's hitting my mirror, and then it's being reflected off my mirror.

So the blue light is the light travelling from my light source, and then the red light is the light that's being reflected back off the mirror.

Now we're going to add some labels to this diagram, which is going to help us to learn and to explain our law of reflection.

So this is what we call the "incident ray." This blue light, the light travelling from the light source, is called the "incident ray." This is called the "reflected ray." So the light that's reflected off the mirror is called the "reflected ray." So you often hear ray of light.

That's how we describe this beam of light.

This dotted grey line here is called the "normal.

' All this line is, is just showing you exactly halfway between the incident ray and the reflected ray.

Now, we looked at angles and recapped the definition at the beginning of the lesson, and they are the amount of turn between two lines.

So we have an angle that we can measure here between the incident ray and the normal, and also an angle that we could measure here between the normal and the reflected ray.

Both of these angles also have a name.

So this is called the "angle of incidence." This blue angle.

And this red angle is called the "angle of reflection." So this is how I remember which is which.

The incident rate and the angle of incidence are the ones that come in to the object.

Okay? So this prefix here helps me to remember.

And then my reflected ray and my angle of reflection are easy to remember because we know the definition for reflection already.

It's when light bounces off the object.

So I can see the light bouncing off here.

Now, this diagram shows us one really important rule about reflection.

And that is that our angle of incidence, so this angle here which I'm going to label i, is always equal to the angle of reflection.

So they're the same size always.

That's the rule.

So i = r.

So this is the law of reflection.

The angle of incidence is always equal to the angle of reflection.

Say it with me.

The angle of incidence is always equal to the angle of reflection.

Let's have a look now at these questions.

So can you complete these on your piece of paper? What should labels A and B say and what is the law of reflection? Pause the video and answer those questions now.

Great.

When you're ready, we'll mark those answers.

So the angle of reflection is always equal to the angle of incidence.

That's your law that you should have written.

So give yourself a tick if you got that right.

And this ray, so ray A, was the incidence ray and ray B was called the reflected ray.

Give yourself a tick if you got those correct as well.

So that brings us to the end of the lesson.

Let's quickly recap our star words before you go and complete your post-lesson quiz.

So we looked at the words "absorbed" and "reflected" at the beginning of the lesson.

"Absorb" means to take something in.

And when something is reflected, it bounces off an object.

An angle is the amount of turn between where two lines meet at their vertex.

And then we learned about two types of material: reflective materials and non-reflective materials.

So reflective materials reflect light well.

Most of the light that hits the surface bounces off.

We've got our diagram there to help us remember.

Non-reflective materials do not reflect light well.

Some light bounces off the object, but most of the light is absorbed.

Then we looked at two types of reflection: specular reflection and diffuse reflection.

And remember, our sticky way to explain those is that specular reflection begins with S, so we remember that it happens on smooth surfaces and the light bounces in the same direction.

So specular reflection is when light bounces in the same direction.

Diffuse reflection is when light bounces in many different directions.

So we remember that 'cause diffuse and different both begin with D.

Make sure you use that when you're doing your post-lesson quiz.

Well done, everybody, for all your hard work today.

I'm really, really impressed.