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.