Print bookPrint book

Week 15 - Explanations, Inventions & Investigations About Light and Vision

Site: MoodleHUB.ca 🍁
Course: Science 8 LearnNet
Book: Week 15 - Explanations, Inventions & Investigations About Light and Vision
Printed by: Guest user
Date: Monday, 17 November 2025, 5:42 PM

Description

.

Table of contents

Introduction

Light and Optical Systems

The sense of sight is extremely important to us, as it provides us with a large part of our information about our world. We are all familiar with light - or think we are. Our eyes respond to the light we receive from objects all around us. Right now you are receiving light from the computer screen you are looking at and in the illustration below you are likely seeing various shades of red, yellow, green and blue against a black background.

How do we see?

What is the something called light that enters our eye and causes the sensation of light?

How does light behave so that we can see the great range of phenomena that we do?


The subject of light will occupy us for this unit.

We see objects in two ways:

The object may be a source of light such as a light bulb, a flame or a star, in which case we see the light emitted directly from the source. The illustration is an example of stars as captured by the Hubble telescope.
More commonly, we see an object because of the light reflected from it. In this case, the delicate pastel shades of this pottery reach our eye only when light from another source is reflected from the pots.
Optical devices improve and extend our vision. Tools such as the telescope and the microscope have helped us extend our knowledge in a variety of fields from the study of cells to the study the universe.

One of the ways we learn about the nature of light and its behavior is thorough the use of geometric ray models. The illustration is a representation of the reflection of light from a flat surface. This is the experimental side of the study of light and its properties.

Welcome to the wonderful world of light!

© 2002 Alberta Online Consortium

Lesson 1

Lesson 1: Challenges
Science in Action 8
Read pages 176 - 181 and make notes in your notebook.




Light is all around us and certainly something that we know about - or do we? How does light make it possible for us to see things? Why can we not see around corners? Why do we see nothing in a completely dark room?


These questions and many others about the nature of light have haunted humans for centuries. In this section, we will examine the thinking of some great scientific thinkers of the past. Then we will take a look at some of the properties of light.

Some of the earliest recorded studies of the nature of light dates back to the times of the ancient Greeks - somewhere in the sixth century B.C. Lets examine the thinking of some prominent scientists: Pythagoras (from ancient Greek times) thought that light was actually beams that came from a person's eyes. When these beams reached an object, the person would see it. The trouble with his theory was that we cannot see in a completely dark room even though our eyes are open. Aristotle (another ancient Greek) thought that light consisted of waves that came from a light source and graveled to the eye. He thought that these waves moved like ripples on water. The seventeenth century A.D. was a very productive time for scientists examining the nature of light. Many discoveries were made on how light travels and how fast it travels.


Newton ( an English scientist) thought that light was a stream of particles that moved from a light source to objects. He worked with prisms to show that white light could be split into all the colors of the rainbow. More interestingly, a second prism could turn all these colors back into white light again. He thought that light of different colors had different amounts of energy. Blue light has more energy than red light, but it has a shorter wavelength.


Huygens (a Dutch scientist) agreed with Aristotle and thought that light moved as waves.

Roemer (a Danish scientist) determined the speed of light using a telescope and the moons of Jupiter. His measurements were quite accurate and showed that all light travels at one speed.

Michelson (an American scientist) confirmed Roemers findings of the speed of light using two findings between tow mountains in California.

Read very carefully the pages assigned in your text to understand some of the properties of light. Your readings will give you evidence for the properties of light summarized below:



1. Light is a form of energy.

2. Light travels in straight lines

3. Light travels at a fixed speed.

Here is a neat web site that discusses some of the properties of light. 


http://www.opticalres.com/optics_for_kids/kidoptx_p1.html

Lesson 2

Lesson 2: Optical Instruments
 
Science in Action 8
Read pages 181 to 191 of your textbook and make notes in your notebook.

The behavior of light has fascinated people for such a long time. Another human fascination with technology soon combined with knowledge of light to give us some tools to extend our abilities. The microscope and the telescope are both based upon the basic properties of light. Of course their function is very different. The microscope letting us see things that are far too small for the human eye. The telescope lets us see things that are really too far away to see well. This section will examine these optical instruments and their effect on our work with light.


Using your text or an encyclopedia, define each of the following terms:
concave
objective lens
refracting telescope
convex
eyepiece lens
reflecting telescope
prism
microscope
objective mirror


Exercise 1.2: Telescopes and Microscopes

 
© 2002 Alberta Online Consortium

Lesson 3

Lesson 3: Interactions with Light: Transmission, Reflection and Absorption

 

Science In Action

Read pages 194 to 199 of your textbook and make notes in your notebook.

 

In this lesson we will investigate how light is transmitted, reflected and absorbed by various materials. Many believe that stained glass is one of the most beautiful art forms. This beautiful window shows us an example of how glass can be made to be transparent, translucent and opaque. By the end of this lesson you will be comfortable with those terms and come to understand how rays of light move and react with various objects.
Light can pass right through some materials. Materials such as clear or transparent glass or plastic allow light to be transmitted without any loss or scattering of the light. So you can see right through something that is transparent. Can you think of any other materials that allow the transmission of light rays.

Some materials are translucent. That means they allow some light to pass through. But before the light can leave the material it is scattered from its straight path. Hold up a piece of white paper to the light and then look at it from the back side. You can see that some light is passing through but you can't see what's on the other side. If glass is etched with sand or acid it will appear frosted and produce the same effect as real frost that covers many windows on cold days.



The frost changes the window from transparent to translucent


This window glass was etched with sand. The etched areas are translucent while the remainder of the window remains transparent


This crystal is translucent

The third type of material will not allow any light to pass through them at all. These materials are said to be opaque. The light can be absorbed or reflected off the surface. When light is absorbed into a material, the energy in that light is converted into some other form. When the sun's light energy is absorbed into the pavement on a city street what kind of energy is it converted into? (Hint: think of a hot summer day and your in bare feet.)

White light is actually combination of different colours of light. If you've ever seen a rainbow, then you have seen the spectrum of colours that makes white light. But what happens when some of the spectrum is absorbed and other parts reflected?

Have you ever heard of 'Roy G Biv'? Its an easy way of remembering the colours in the spectrum that make up white light! The name stands for red, orange, yellow, green, blue, indigo and violet. Now we can go back and answer our question: What happens when some of the light is absorbed and others parts reflected?

Let's answer the question with the help of the artist's pallet. In the case of the red blob of paint all colours are absorbed except for red. In this case the red light is reflected and we see red paint while the colours orange, yellow, green, blue, indigo and violet are absorbed.

Studying Light as a Ray

Scientists use many models when they are studying light. That is because no one model adequately describes all the characteristics of light. At times they study it as a ray, while at other times they model it as a wave.

In this lesson we use the geometric ray model to describe some of the characteristics of light. A ray is considered to be a straight line which represents a beam of light. Here are a couple of ways to prove that light travels in a straight line.

Another wonderful observation that proves that light travels in a straight line is from the heavens above. When light from the sun strikes opaque objects like trees or buildings it creates a shadow behind the object. A second and much more dramatic example is a solar eclipse. There is also a lunar eclipse. This is where the earth blocks the light from the sun and casts a shadow on the moon.

Is there any simple way of testing this model? If you choose, you could make a pinhole viewer (Science In Action 8, page 185).  For instructions on how to make a pinhole camera click here.(or at http://www.exploratorium.edu/sln/light_walk/pinhole_todo.html )

Although you might not have used these scientific terms, you know that you can't see around corners so you have an understanding that light doesn't bend or curve on its own. It must strike something before it can change course.

Exercise 1.3: Ray Diagrams

 

 

So what did you discover?

The 'law of reflection' states: the angle of incidence of a ray equals the angle of reflection.

 

© 2002 Alberta Online Consortium

Lesson 4


Lesson 4: Transparent Objects can Refract Light
Science In Action
Read pages 200 - 203

Have you ever been playing in a swimming pool and seen something on the bottom while you were sitting on the edge? But when you went under water to retrieve it, it was in a different place. If this has happened to you then you were the victim of refraction. When light enters a medium (material) like water it slows down a bit. If it enters at an angle to the surface of the water this change in speed causes causes the ray of light to bend away from its original path. This is called refraction.


Fly fishermen often try to cast to a fish they can see underwater. After reading about refraction, where would you cast your line?
Traveling at the Speed of Light!

The change in speed of the light beam is dependent on the density of the material it is passing through. Therefore the amount of bending of the beam from its original course is depends on the density of the transparent material. Scientists have measured each of these materials and given each a 'refraction index' or a measure of the amount of bending for each material.
 

The Science Behind Refraction

Examine the diagram below,  you should be able to label this diagram from memory.




Exercise 1.4: Studying Refraction
© 2002 Alberta Online Consortium

Section 1 Notes

You will have two opportunities to write this section quiz. This quiz consists of 10 questions. Use the results from your 1st attempt to help you prepare for your second attempt. Your best score will be taken as your assessment mark. You have 15 minutes to complete this multiple choice quiz.

Click the icon to go to the quiz.