Science Grade 8 Name : HR : ScE8.2 : Optics · flashlights Use: so you can see yourself accurately Type of mirror: 5.Reflecting mirrors in headlights and Use: to focus the light into

ScE8.2 Optics – p.1

Science Grade 8 Name : ___________________________ HR : _____

ScE8.2 : Optics

ScE8.2.1 Light

ScE8.2.2 Reflection and Mirrors ScE8.2.3 Refraction and Lenses

ScE8.2.1: Light

1. Early Theories of Light (p.132 et 135) 2. The Speed of Light (p.135-136) 3. Optical Technologies (p.133-134) 4. Properties of Light :

a. Rectilinear propagation (p.175) b. Propagation through vacuum

c. Propagation through substances (p.173-174) d. Reflection (diffuse and specular) p.176-177 e. Refraction (p.149, 1179)

f. Dispersion (p.149)

5. Waves and the Wave Model of Light (p.138-140) 6. The Electromagnetic Spectrum (p.156-160)


Terms Amplitude Wavelength Refraction

Crest Opaque Spectrum

Trough Rectilinear propagation Specular reflection

Diffuse reflection Reflection Translucent

Dispersion Frequency Transparent

1. _________________________ : a property of light that says it travels in a straight line

2. _________________________: see-through; lets light travel clearly through it

3. _________________________: cloudy; lets light through but not clearly.

4. _________________________: doesn’t let light travel through it at all.

5. ___________________________ : when light bounces off a surface

6. ___________________________ : when light bounces off a glossy surface and forms an image of the surroundings

7. ___________________________ : when light bounces off a rough surface and does NOT

form an image of the surroundings.

8. ___________________________ : when light makes a bend as it passes from one substance into another.

9. ___________________________ : when the different colours of white light are separated into a rainbow

10. ___________________________ : the number of waves per second

11. ___________________________ : the distance between two crests or two troughs of a wave.

12. ___________________________ : the height of the crest or the depth of the trough of a wave

13. ___________________________ : the highest point of a wave.

14. ___________________________ : the lowest point of a wave.

15. The electromagnetic ___________________________ : the series of electromagnetic waves

ranging from the longest wavelength (low energy) to the shortest (high energy)


The First Theories of Light

1. Describe two theories first proposed by the early Greeks to explain light and how our eyes can see. Which theory do scientists still use?

2. How did Galileo first attempt to measure the speed of light? Why was this method not successful?

3. How did Michelson eventually succeed in measuring the speed of light?

4. What is the speed of light?

5. In a thunderstorm, why do we see the lightning before we hear the thunderclap? How can you

tell how far away was the lightning based on the length of the delay between the two?

6. Give 5 examples of optical technologies.


The Properties of Light

List the 6 properties of light

1.

2.

3.

4.

5.

6.

1. Rectilinear propagation What is rectilinear propagation? What effect does it cause? Use a diagram to explain.

2. Propagation through a vacuum What is a vacuum? Give two examples of light travelling through a vacuum.

Why is it interesting that light can travel through a vacuum?


3. Propagation through substances Complete the following table to compare transparent, translucent, and opaque substances.

Definition Examples

Transparent

Translucent

Opaque

4. Reflection What is reflection? Give an example. What is the difference between specular and diffuse reflection?


How does diffuse reflection allow us to see the colour of something?

5. Refraction What is refraction? Give an example.

6. Dispersion What is dispersion? Give an example.

Application Identify which property of light is represented in each situation.

Situation Property of light

Light from stars can be seen from the earth

Light travels through air.

You see that an apple is red.

You see a rainbow in the sky after a rain.

On a sunny day, you cast a shadow on the ground.

You see shiny reflections in the glossy paint of a car.

You see sheet of paper, with no reflections in it.

You see yourself in a mirror.


Properties of a Wave On this diagram of a wave, label the crest, the trough, the amplitude, and the wavelength. Using a ruler, measure and label the wavelength and the amplitude of the wave.

What is the frequency of a wave? What is the relationship between the wavelength, the frequency, and the energy of a wave?

Practice activity: Measure the wavelength and the amplitude of each of the following waves. Which one has the least amount of energy? Which one has the highest frequency?

The Electromagnetic Spectrum

Sketch a diagram of the electromagnetic spectrum.


The Different Wavelengths of Radiation in the Electromagnetic Spectrum

Type of radiation

Uses Danger (if applicable)

Gam

ma

rays

X r

ays

Ult

ravi

ole

t ra

ys

Vis

ible

ligh

t

Infr

ared

ligh

t

Mic

row

aves

Rad

io w

aves


Review for Quiz ScE8.2.1 Answer on your own paper.

1. What was Pythagoras’s theory of light?

2. How did Galileo attempt to measure the speed of light? Why was this method not successful?


4. What travels faster, light or sound?

5. Name 5 examples of optical technologies.

6. List the 6 properties of light.

7. Identify the property of light represented in each situation.


We see light from the sun.

Light comes in through the windows.

Trees are reflected in a still pond.

You use a glass prism to turn white light into rainbows.

On a hot summer day, you can protect yourself from the sun in the shadow of a tree.

You can see the pink colour of a t-shirt.

You can see your reflection in a windowpane.

8. Explain the difference between diffuse and specular reflection and give an example of each.

9. Explain how diffuse reflection allows us to see colours.

10. Draw a diagram of a wave and label the crest, the trough, the amplitude, and the wavelength.

11. What is the frequency of a wave?

12. If a wave has a HIGH frequency – is it high or low energy? Does in have a long or short

wavelength?

13. Sketch the diagram of the electromagnetic spectrum, showing all wavelengths of radiation

from radiowaves to gamma rays.

14. In the electromagnetic spectrum a. Which type of radiation has the longest wavelengths? b. Which as the shortest wavelengths? c. Which has the most energy? d. Which as the least energy?

15. Name one use for each type of radiation. Nomme une utilisation de chaque type de radiation.

16. Why are gamma rays so dangerous?

17. What is the possible danger with ultraviolet rays?

18. Why do doctors only use Xrays when there is a good reason for them?


ScE8.2.2 : Reflection and Mirrors

Outline and Study Guide 1. Exploration activities : hand mirrors

and ray boxes. 2. The law of reflexion (p.178) 3. Lab activity: reflection in a plane

mirror (ray box) 4. Ray diagrams for plane mirrors.

(p.189) 5. Real and virtual images 6. Activity : Images in hand-held plane

and curved mirrors. 7. Lab activity : Reflected rays in curved

mirrors (ray box) 8. Curved mirrors : focal point,

principal axis, vertex. (p.198, 204) 9. Ray diagrams with curved mirrors

Principal axis Focal point Plane Reflection

concave Angle of incidence Real image Vertex

convexe Incident ray Reflected ray Virtual image

Normal

1. ___________________________ : the light ray that hits the mirror

2. ___________________________ : the light ray that bounces off the mirror

3. ___________________________ : an imaginary line perpendicular to the surface of the mirror

4. ___________________________ : the angle between the incident ray and the normal

5. ___________________________ : the angle between the reflected ray and the normal

6. ___________________________ : a flat surface

7. ___________________________ : a curved surface like the inside of a sphere

8. ___________________________ : a curve surface like the outside of a sphere

9. ___________________________ : with a curved mirror, the point of intersection of all

incident rays parallel to the principal axis.

10. ___________________________ : an imaginary like perpendicular to the centre of a curved

mirror

11. ___________________________ : the point in the centre of the surface of a curved mirror where the principal axis meets the mirror.

12. ___________________________ : an image formed when the reflected rays really intersect in front of the mirror.

13. ___________________________ : an image formed behind the mirror where the reflected

rays appear to come from.


Exploration A : Where to hang a mirror? Where should you place the mirror when the two students are at the same distance from

the wall?

_______________________________________________________ _______________________________________________________ Where should you place the mirror when one student is closer to the wall than the other?

_______________________________________________________ _______________________________________________________

Exploration B : Using a ray box From the activity shown by your teacher, what do you notice about the angles of the light

rays and the mirror?

_______________________________________________________ _______________________________________________________ _______________________________________________________

Rays and Angles in Reflection

Complete the diagram shown by your teacher and label

• The mirror • The incident ray

• The reflected ray • The normal • The angle of incidence

• The angle of reflection

State the Law of Reflection :

_______________________________________________________ _______________________________________________________


Ray Diagrams for Plane Mirrors

Copy along as your teacher shows on the board how to construct a ray diagram to find the image of the snow flake.

Second example.


Now practice!

For a bigger more complicated object use the « trick with the normal » to find the image of several points on the object, and then draw the rest of the image


Real vs Virtual Images Observe your teacher’s demonstration of a real image with a mirascope. Explain the difference between a real and a virtual image.

Curved Mirrors : Concave and Convex What is the difference between concave and convex?

Exploration : Comparing Images in Plane and Curved Mirrors

Material : hand-held mirrors : one plane, one concave, and one convex. One small sticker.

Method : Put the sticker on the tip of your finger, and hold a mirror with the other hand. Observe the image of the sticker in the mirror. Move your finger close up and farther away and compare what happens. Repeat for each kind of mirror.

.

Plane Mirror Characteristic of the image in the mirror Your observations

S Size Bigger or smaller than the object?

P Position

Is the image in front or behind the mirror?

Is it closer or further away from the mirror than the object?

O Orientation Right side up or upside down?

T Type Real or virtual?

Do your observations change if the object is closer or further away from the mirror?

How?


Convex Mirror Characteristic of the image in the mirror Your observations


P Position

Is the image in front or behind the mirror?

Is it closer or further away from the mirror than the object?




How?

Concave Mirror Characteristic of the image in the mirror Your observations


P Position Is the image in front or behind the mirror? Is it closer or further away from the mirror than the object?




How?


Identify the type of mirror (plane, concave, convex) used in each situation.

1.Bathroom mirror

Use : so you can see yourself accurately

Type of mirror :

5.Reflecting mirrors in headlights and

flashlights

Use : to focus the light into a strong beam

Type of mirror :

2.Surveillance mirror in a store

Use : so the staff can see the whole store

Type of mirror :

6.Makeup mirror

Use : to make your face seem bigger so you

can see details better

Type of mirror :

3.One way mirror

Use : You can see through from one side

but not from the other.

Type of mirror :

7.Side view mirror

Use : so you can see a wider area behind

you

Type of mirror :

4.Dentist’s mirror

Use : to make your tooth seem bigger so

the dentist gets a better look.

Type of mirror :

8.A disco ball

Use : to create small light rays that sweep

across the room.

Type of mirror :


Characteristics of Curved Mirrors

Sketch diagrams curved mirrors and their

characteristics, labelling • The mirror

• The principal axis • The focal point • The vertex

• Incident rays parallel to the principal axis

• Reflected rays

Concave mirror (p.198)

Convex mirror (p.204)


Ray Diagrams for Curved Mirrors

Important rays

Parallel incident rays ------> Reflect through the focal point.

Incident rays through the focal point -------> Reflect parallel

Steps for finding the image in a curved mirror

1. Incident ray parallel ------> Reflect through the focal point.

2. Incident ray through focal point -------> Reflect parallel 3. Where the REFLECTED rays meet -------> the top of the image. 4. The base of the image is on the principal axis

5. Sketch the rest of the image 6. SPOT characteristics


Ray Diagrams for a Convex Mirror :

Ray Diagrams with a Concave Mirror

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Practice

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Review for Quiz ScE8.2.2 Answer on your own paper.

1. State the law of reflection.

2. Construct a ray diagram to find the image of the flower behind the mirror.

3. Explain why convex mirrors are used for surveillance in stores.

4. Name two uses for concave mirrors.

5. What type of curved mirror is used for a solar oven?

6. Explain the difference between a real and a virtual image. 7. What type of mirror produces an image with the following characteristics?

Characteristics Type of mirror

(plane, concave, or convex)

An image that is always right side up and smaller than the object.

An image that is always right side up and the same size as the object.

An upside down image, smaller than the object.

A mirror that concentrates the heat of the sun in a solar oven.

A right side up image behind the mirror that is always the same distance from the mirror as the object.

A mirror that lets you see a large area behind you.

A mirror that lets you see your face more closely.

An image that is right side up and bigger than the object.

A mirror that concentrates the light of a flashlight into a beam.


8. a) Construct ray diagrams to find the image of the ipod in each case

b) Describe the SPOT characteristics. c) When you are done, compare all the diagrams to describe what happens to the image

as an object gets closer and closer to a convex mirror.


9. a) Construct ray diagrams to find the image of the rope-skipper in each case

b) Describe the SPOT characteristics. c) When you are done, compare all the diagrams to describe what happens to the

image as an object gets closer and closer to a concave mirror.


ScE8.2.3 : Refraction and Lenses

Outline and Study Guide 1. Refraction

a. Examples

b. Incident and refracted rays and angles. (p.182) c. Lab activity : Refraction in water (p.184-185) d. Refraction and the wave model of light

2. Lenses a. Exploration : Convex

(convergent) and concave

(divergent) lenses (hand-held and ray box)

b. The human eye c. Near- and far-

sightedness, and

corrective glasses.

Terms

Convergent Divergent Lens Near-sighted Far-sighted

Refracted ray Refraction angle

1. ___________________________ : the ray after refraction

2. ___________________________ : the angle between the refracted ray and the normal

3. ___________________________ : a curved piece of transparent material that refracts light to

form images.

4. ___________________________ : coming together

5. ___________________________ : spreading apart

6. ___________________________ : when your eyes can see clearly close up but not from a distance.

7. ___________________________ : when your eyes can see clearly from a distance but not close up.


Refraction 1. Draw two examples of refraction shown in class

2. Refraction of light rays Copy the diagram of refraction shown by your teacher.

In this diagram, light goes from ____________ to ______________.

On your diagram, label

• The two substances

• The incident ray

• The refracted ray

• The normal

• The angle of incidence

• The angle of refraction


Lab Activity : Refraction Through Water

Question: Which way does light bend when going from one substance into another?

Hypothesis: Predict : a) Which way will light bend when entering from air into a denser substance?

b) Which way will it bend when going from the denser substance into the air?

Material: • Ray box • white paper • ruler • protractor • water • transparent plastic box

Procedure:

1. Put water in the box and place it on the sheet of paper, and trace the outline of the

box.

2. Use the ray box to direct a single ray to enter the box at an angle, and observe where

the exiting ray comes out. Use dots to mark the position of the entering and exiting rays.

3. Remove the box and use the ruler to mark the path of the light going in, through, and

out of the box.

4. Use your protractor to draw accurately the normals at the points where the light enters and leaves the box.

5. Measure the angles of incidence and refraction when the light goes from air into water. Then measure the angles of incidence and refraction when the light comes out

of water and into the air.

6. Record your angles and those of other students in your group in the Table of Results.


Table of Results

Name of student

When light goes from air to

water

When light goes from water

to air

Angle of incidence

Angle of refraction

Angle of incidence

Angle of refraction

Conclusions: Considering your group’s results,

1. Do you notice a pattern in the angles?

2. Which way does the light bend when going from the air into water which is denser,

towards the normal or away from it?

3. Which way does the light bend when coming out of the water into air which is less dense?


How the Wave Theory of Light Explains Refraction How does the speed of light change when it enters into a more dense substance, like going from air to water or glass ? How does this change in speed cause the light ray to refract when entering the denser substance?

Use a prism and a light box to determine which colour of the rainbow is refracted the MOST: the red or the purple? Based on this, which wavelength is refracted the most: longer or shorter waves?


Lab Activity ScE8.2.3 : Exploring Lenses

Purpose: to compare concave and convex lenses to see what it’s like when you look

through them and to observe the path of light rays when they are refracted through each

kind of lens.

Materials : ✓ Hand-held lenses (for looking through) ✓ Ray box with table lenses. ✓ White paper

✓ Pencil and ruler

Procedure : 1. Observe the lenses. Make a little sketch that shows the difference in shape between a

concave and a convex lens, and label each one.

2. Look at something close up with both kinds of hand-held lenses. Notice if the object looks bigger or smaller with each lens. Move each lens back and forth to change distance from the object and notice what happens. Write down your observations.

a. Convex lens :

b. Concave lens :

3. Use the ray box and the table lenses. a. Make a line for the principal axis, place the lens on the paper and trace it with your pencil. b. Adjust the ray box so the 5 rays are exactly parallel. c. Put the ray box so that the 5 parallel rays go through the lens. Use dots to mark the position

of the incident and refracted rays. d. Take your sheet of paper and use the ruler to mark the path of the light rays. e. Mark the focal point F where the refracted rays meet. If the refracted rays do not meet in

reality after the lens, extend them back before the lens to the point where they would meet. Measure the focal lens in cm and record it on your diagram.


f. Draw diagrams of your results in the following spaces. Label each diagram: the lens, the principal axix, the incident rays, the refracted rays, and the focal point.

Convex Lens Focal length : ______

Concave Lens Focal length : ______

Conclusions : 1. Which type of lens is converging? ________________________________________

2. Which type of lens is diverging? ___________________________________________


Refraction and the Human Eye

Use the following diagram to explain how the human eye works:

Near-sightedness and Far-sightedness What is near-sightedness?

What is far-sightedness?


Compare the ray diagrams for near- and far-sighted vision and complete the chart below

Normal Eye Near-sighted eye Far-sighted eye

Length of eye compared to normal

Where the

image forms without glasse

Type of lens for glasses


Optical Instruments Using Lenses Camera

Galileo’s telescope

Compound microscope


Review for Unit Test ScE8.2 Optics To be completed on your own paper.

Study ALL the definitions in the booklet!

Section ScE8.2.1 : Light and Its Properties

1. What was Pythagoras’s theory of light?

2. How did Galileo attempt to measure the speed of light? Why was this method not successful?


4. What travels faster, light or sound?

5. Name 5 examples of optical technologies.

6. List the 6 properties of light.

7. Identify the property of light represented in each situation.


We see light from the sun.

Light comes in through the windows.

Trees are reflected in a still pond.

You use a glass prism to turn white light into rainbows.

On a hot summer day, you can protect yourself from the sun in the shadow of a tree.

You can see the pink colour of a t-shirt.

You can see your reflection in a windowpane.

8. Explain the difference between diffuse and specular reflection and give an example of each.

9. Explain how diffuse reflection allows us to see colours.

10. Draw a diagram of a wave and label the crest, the trough, the amplitude, and the wavelength.

11. What is the frequency of a wave?

12. If a wave has a HIGH frequency – is it high or low energy? Does in have a long or short

wavelength?

13. Sketch the diagram of the electromagnetic spectrum, showing all wavelengths of radiation

from radiowaves to gamma rays.

14. In the electromagnetic spectrum a. Which type of radiation has the longest wavelengths? b. Which as the shortest wavelengths? c. Which has the most energy? d. Which as the least energy?

15. Name one use for each type of radiation. Nomme une utilisation de chaque type de radiation.

16. Why are gamma rays so dangerous?

17. What is the possible danger with ultraviolet rays?

18. Why do doctors only use Xrays when there is a good reason for them?


Section ScE8.2.2 : Reflection

1. State the law of reflection.

2. Construct a ray diagram to find the image of the flower behind the mirror.

3. Explain why convex mirrors are used for surveillance in stores.

4. Name two uses for concave mirrors.

5. What type of curved mirror is used for a solar oven? 6. Explain the difference between a real and a virtual image.

7. What type of mirror produces an image with the following characteristics?

8.

Characteristics Type of mirror

(plane, concave, or convex)

An image that is always right side up and smaller than the object.

An image that is always right side up and the same size as the object.

An upside down image, smaller than the object.

A mirror that concentrates the heat of the sun in a solar oven.

A right side up image behind the mirror that is always the same distance from the mirror as the object.

A mirror that lets you see a large area behind you.

A mirror that lets you see your face more closely.

An image that is right side up and bigger than the object.

A mirror that concentrates the light of a flashlight into a beam.


Practice ray diagrams with curved mirrors

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Section ScE8.2.3 : Refraction 1. Give two examples of refraction.

2. Draw a diagram of a light ray refracted as it goes from air to water. On your diagram, label

• The two substances

• The incident ray

• The refracted ray

• The normal

• The angle of incidence

• The angle of refraction 3. When a light ray goes from air into a denser substance, which way does the light bend?

4. When a light ray comes out into the air from a denser substance, which way does the light

bend?

5. How does the speed of light change when it enters a denser substance?

6. How does this change in speed cause the light ray to refract when entering the denser substance?

7. Which colour of light is refracted the most by a prism, the red or the violet?

8. Which wavelength of light is refracted more, long or short waves?

9. Use small sketches to show the difference in shape between

• A convex mirror

• A concave mirror

• A convex lens

• A concave lens

10. Draw a diagram to show refraction by a convex lens. Label the principal axix, the incident rays, the refracted rays, and the focal point.

11. Draw a diagram to show refraction by a concave lens. Label the principal axix, the incident rays, the refracted rays, and the focal point.

12. Which type of mirror is convergent? Which type is divergent? Sketch ray diagrams to justify your answers.

13. Which type of lens is convergent? Which type is divergent? Sketch ray diagrams to justify your

answers.

14. What type of lens do you need in your glasses if you are near-sighted? What type do you need if you are far sighted?

15. Name three optical instruments that use lenses.

Documents

Science Grade 8 Name : HR : ScE8.2 : Optics · flashlights Use: so you can see yourself accurately Type of mirror: 5.Reflecting mirrors in headlights and Use: to focus the light into