The upcoming three chapters; light, reflection and curved mirrors, will be studied and discussed in groups. We will spend the upcoming 7/8 lessons on these chapters. You will have to make a wordlist, which needs to be handed in for a mark. In these chapters you can also find a lot of small experiments. You have to finish all of these experiments before the test, we will check this. The test will be on chapter 22 (light), chapter 23 (reflection) and chapter 24 (curved mirror).
Since you will be doing everything in groups, I made this site to help out with any questions you might have. I will also be listing all the lesson targets per chapter so you can check these before the test.
Light reflecting off mirrors
For every chapter you will find the lesson targets, additional explanations and some questions or games. At the end of the site you will also find a practice test you can make before the real test, to see what you still need to learn. Goodluck!
chapter 22 light
Targets for this chapter
At the end of this chapter you will:
know how to explain light with examples.
know light is a wave motion.
be able to calculate a light year using the speed of light.
know how shadows come to life.
be able to draw the umbra and penumbra.
be able to explain an eclipse.
know how a pinhole camera works and creates and image
Explanation
We talked about light as a from of energy, in this chapter we will be looking into light even more. The light we can see is what we call visible light. Light is a wave motion, just like the waves we see when going to the sea. The light we can see has a wavelentgh of 1/2000 of a millimetre, which is only a bit bigger than some molecules!
When we look around there are lots of objects that produce their own (visible) light, like the sun, a lamp and your screen. These objects are luminous sources. While other objects can only be illuminated by the light. They reflect the light right into your eyes, the moon is a great example of this.
Light travels in straight lines, these lines are rectilinear (this means when something moves in a straight line). When doing experiment 22.1 you will be using a raybox like shown on the picture. This box shines a narrow beam of light, also called a ray, across the paper using using a small slit on the front and a lamp in the back.
Shadows
When these rays of light travel trough the air, they sometimes get stopped by objects in their way. This will create a shadow. There are different kinds of shadows, these depend on the source of light you are using. The first shadow comes from a smaller source of light. This light will create a very dark shadow if you hold an object in front of it. The dark shadow is called the umbra, in Dutch we would call this 'de kernschaduw'. The seconds shadow comes from a bigger source of light. This light will create the dark shadow but will also be surrounded by less dark, partial shadow. This shadow is called the penumbra, in Dutch this is called 'de halfschaduw'.
If you hold your hand above the table in a classroom, what do you see? And what is the difference if you shine a flashlight on your hand?
Eclipses
Eclipses happen due to the shadows that the Moon or the Earth create. There are 2 types of eclipses. A solar eclips and a lunar eclips. In the vide below they explain the differences between these two eclipses!
The pinhole camera
However photography was only invented in 1839 the principle of the pinhole has been known since ages. As early as the 4th century B.C. this phenomenon was mentioned by Aristotle in one of his writings. Light falling through a small opening between the leaves of a tree gives a perfect projection of the sun on the ground. Even though the opening between the leaves has a shape which is irregular and is not perfectly round, yet the image on the ground is. Aristotle could never explain this. Nowadays a simple pinhole camera consists of a closed box, with a screen on one side and a pinhole on the other side. The light that goes trough this pinhole creates an image on the screen. When you look at the image that was created it will be inverted, so it's upside down and turned left-to-right. When using a smaller hole, a sharp but dark image. While a larger hole will give you a blurry but birght image.
know the difference between regular and diffuse reflection.
Explanation
You might have noticed that when it's sunny outide, the sunlight gets reflected by jewelry or a phone screen.
When you've finished experiment 23.1, you will see that the angles you measured are about the same. This is called the law of reflection, in the picture below you can see how the reflection angle is the same as the angle of incidence.
If you want some extra explanaining about this law and how to use it, I made this video you can watch!
Periscope
Perhaps you ever wondered how a submarine could be under water, yet they still managed to look over the water. They can do this because they use a periscope. A periscope uses the law of reflection, by placing two different mirrors at certain angles.
This way you can make your own periscope, pretty easy!
The image in a plane mirror
When an object is in front of a mirror, the mirror will show an image of this object. This image has the same distance to the mirror, as the object in frommt of it. So if you look in the mirror with a distance of 0,50 m, your image will also be 0,50 m from the mirror. The image in the mirror is called a virtual image, since it appears to be behind the mirror.
Regular and diffuse reflection
In this chapter we have discussed regular reflection by plane mirrors. But what happens when a mirror is curved? Then your reflection will be diffuse, meaning it is reflected in different directions.
recognise the influence of these mirrors on the rays of light.
know what concave mirrors are used for.
know what convex mirrors are used for.
Be able to draw a diagram with a concave mirror.
Explanation
Last chapter was mostly about plane, flat mirrors.
In this chapter we will talk about curved mirrors. There are two types of curved mirrors: first we have a concave mirror, which curves in (like a cave). Second we have a convex mirror, these curve outward.
When a mirror is curved, the light gets reflected differently. Use https://ricktu288.github.io/ray-optics/simulator/ to build different curved mirrors and see how the light gets reflected. You can look at the following tutorial on the applet.
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Auteur
J Moed
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2020-04-25 16:32:14
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2. drawing shadows
