California science grade 3 (13)

Students know light is refl ected from mirrors and other surfaces... Make a Prediction What happens to light when it hits a mirror?. Can you make light bounce off the mirror and shine on

CHAPTER 8

Light

What is light and how does it travel?

342

Lesson 1 How Light Moves

Lesson 2 Seeing Light and Color

Lesson 3 Shadows

3 PS 2 Light has a source and travels in a direction.

343

answers in the text

ELA W 3.2.1 Write narratives:

a Provide a context within

which an action takes place

b Include well-chosen details

to develop the plot c Provide

insight into why the selected

incident is memorable.

344

Write About It

Response to Literature The poet tells about

an experience he had with light How did the experience make him feel? Write a personal narrative about an experience you have had with light It might be a rainbow, a sunrise,

or a sunset Tell how you felt about the

experience and why it is memorable

The prism bends a beam of light

And pulls it into colored bands.

My fingers tremble with delight:

I hold a rainbow in my hands.

by Lawrence Schimel

- Journal Write about it online

@www.macmillanmh.com

345

How Light

Moves

When you look at a mirror, glass, water, or other shiny thing, you can see yourself Why does this happen? How does light make this possible?

Lesson 1

3 PS 2.b Students know light is refl ected from mirrors and other surfaces.

346

ENGAGE

Step

How does light move?

Make a Prediction

What happens to light when it hits a mirror?

Test Your Prediction

Hold a mirror in front of you Have a partner

shine the flashlight onto the mirror

Observe What happens to the

flashlight’s beam?

Experiment Pick a spot on the wall or

chalkboard Can you make light bounce off the

mirror and shine on that spot? How? Do you

have to move the mirror, the flashlight, or both?

Draw Conclusions

What happened to the beam of light when

it hit the mirror? What happened when you

moved the mirror? What happened when

you moved the flashlight?

Communicate Make a drawing to show

how light moves

Explore More

Experiment Sit next to your partner and hold

the mirror so that you can see your partner Can

your partner see you in the mirror? Can you see

yourself and your partner in the mirror at the

same time?

Materials

mirror

flashlight

3 IE 5.e Collect data in an investigation and analyze

those data to develop a logical conclusion.

347

EXPLORE

C Main Idea

Light is a form of

energy When light hits

an object, some light

is reflected Reflected

light changes direction

and keeps moving in a

To understand color, you must learn about light Light is a form of energy Light is made up of transverse waves that move up and down.

Visible Light

You can see some waves of light energy Color is light energy we can see Light you

can see is called visible light The beam of a

flashlight and flash of a camera are visible light Everything you see with your eyes is because of visible light.

B Radio waves are used to transmit signals for cellular phones, radios, and televisions

BMicrowaves are used to cook food

Infrared waves are felt as heat This photo was taken with film that shows infrared light

Forms of Light Energy

radio waves microwaves infrared waves

3 PS 2.b

348

EXPLAIN

Invisible Light

Other forms of light energy are not visible

X-ray waves are a form of light energy that

you cannot see We use X-ray waves to take

pictures of bones and teeth The waves given

off inside a microwave oven are another

form of invisible light energy You cannot see

microwaves but you can see how they change

uncooked foods.

Quick Check

Problem and Solution You fell and hurt

your ankle How can you find out if you

Visible light waves are the

only light energy we can see

We see these waves as the

colors of the rainbow

visible waves ultraviolet waves X-ray waves gamma waves

High-energy gamma waves are used in nuclear power plants B

349

EXPLAIN

How does light travel?

All forms of light energy are alike

in one way Light always travels in

a straight path Visible light moves

outward from a lamp in a straight

path The microwaves in a microwave

oven move in a straight path Even

light energy from the Sun travels

millions of miles through space in

straight paths.

Reflection

Have you ever played tennis?

After you hit the ball toward the

ground, it bounces upward Light

acts much like a tennis ball When

light hits an object, it bounces

off in a different direction Then

it continues moving in a straight

path The bouncing of light waves

off an object is called reflection

(ri•FLEK•shuhn)

Reflection

How is the path taken

by the tennis ball similar

to the path of light that reflects off a mirror?

Clue: Pictures can show movement and direction

Read a Photo

Light is like a bouncing tennis ball When it hits a surface, it bounces off in a new direction

350

EXPLAIN

Quick Check

Problem and Solution How

can you see yourself if you do

not have a mirror?

Critical Thinking Is it possible

to see in the dark? Explain.

D When you look in

a mirror you see an image of yourself

Movement of Light

Use a pencil and carefully poke

a hole in two index cards Hold the cards upright on a flat surface so that the holes are lined up

Observe Place a lit flashlight directly behind the last card Then bend your body so that you are eye level

with the first card

Can you see the flashlight’s beam?

Predict What will happen if you move one of the cards?

Will you still be able

to see the light?

Write down your prediction and make a drawing of how you think the light will move

Observe Move the second card

a little to the right Again bend your body so that you are eye level with the first card Can you see the flashlight’s beam now?

Draw Conclusions What caused differences in your observations? Make another sketch to explain how light travels

What do you notice about

the path of the laser light?

Smooth, shiny surfaces reflect

almost all the light that strikes

them These surfaces can be used

as mirrors Light bounces off

them in one direction and forms

a picture called an image

351

EXPLAIN

What happens when light hits

a rough surface?

A smooth, shiny mirror reflects light very

well and shows a clear image A mirror with

a scratched surface will not reflect a clear

image Why?

When light hits a rough surface, it

bounces off in different directions Because

of this, a clear image does not form You can

see yourself on the surface of a calm pond If

the water is rough and swirling, a clear image

does not form This is because the light is

reflected in many different directions.

Quick Check

Problem and Solution If you were

planning a building that reflects the sky,

what kind of material would you use?

Critical Thinking Have you ever looked

at your reflection in a pool of water? Why

do you think a pool of water can act like

a mirror?

A Light that hits a rough surface is reflected in different directions

A When light hits a rough pond, it bounces off

in different directions You cannot see a clear image on the surface

352

EXPLAIN

Think, Talk, and Write

Main Idea What is light?

Vocabulary What is a reflection?

Problem and Solution Why can you see yourself in the base of a silver spoon but not at the bottom of a plastic bowl?

Summarize the Main Idea

- Review Summaries and quizzes online @www.macmillanmh.com

Write a Paragraph

Count the number of mirrors in

your home Are there many? We

don’t think about mirrors, but

they are very useful tools Write a

paragraph listing at least five uses

for mirrors

Solve a Problem

One side of a rectangular mirror

is 8 feet long Another side of the rectangular mirror is 10 feet long

What are the lengths of the other two sides of the mirror?

reflection (p 350–351)

If light hits a smooth

surface, a clear image

forms Light that

hits a rough surface

scatters (pp 350–352)

Critical Thinking How is a reflection

in a mirror different from the object

in front of the mirror?

Test Practice How does light travel?

When you experiment, you make and follow a

procedure to test a hypothesis It is important to record what you observe during an experiment Once you

have enough information, you can decide whether your hypothesis is supported or disproved

Try It

In the following experiment, you will test the

hypothesis that light moves in a straight path Follow the steps of the procedure Then use your observations to draw a conclusion

354

EXTEND

Draw a target on a sheet of white

paper Hang it on a wall near your

desk or table

Stand two mirrors in clay as

shown Then shine a flashlight into

one mirror Draw or write your

observations on a chart

Move the light or the mirror until the

light is reflected in the other mirror

Record your observations

Continue to move the light or

mirrors until the light is reflected

off your target

Shine the flashlight from a higher,

then a lower angle Record your

observations

Draw Conclusions

C How did you make the light hit the

target? Does light always move in a

straight path?

C Did your observations support or

disprove the hypothesis?

Apply It

Now do another experiment Put the

mirrors back in place Place a small object

between them How many reflections do

you see? Move the mirrors closer together,

then farther apart How many reflections

do you see each time? Remember to

record your observations

What I Did What I Observed shine the light

in one mirror

made light refl ect in the other mirror shine the light from a higher angle

shine the light from a lower angle

3 PS 2.b Students know light is refl ected from mirrors and other surfaces 355

EXTEND

Lesson 2

3 PS 2.c Students know the color of light striking an object affects the way the object is seen • 3 PS 2.d Students know an object is seen when light traveling from the object enters the eye.

356

ENGAGE

How does light affect the color

you see?

Form a Hypothesis

Will the color of an object appear to be different

if you look at it through a colored filter?

Test Your Hypothesis

Predict Look at a sheet of white paper and

a few sheets of colored paper What color

will each sheet of paper appear to be if you

observe it through the blue filter? The red?

The green? Write down your predictions

Experiment Look at the white paper and

the colored paper through the red filter

Repeat for each of your colored filters Make

a list of all the colors that you see

Draw Conclusions

Compare How do your observations

compare to your predictions? How do

they differ?

Analyze Data Why did you see

different colors?

Explore More

Experiment What color will a white object be

if you look at it through a blue filter? What if you

look through both a blue and a red filter at the

same time? Try it and explain what you see

Materials

sheets of colored paper

sheets of colored plastic

3 IE 5.d Predict the outcome of a simple investigation

and compare the result with the prediction.

357

EXPLORE

C Main Idea

You see an object when

reflected light enters

your eyes The color of

light that bounces off an

object gives the object

How do you see?

You know that light reflects or bounces off objects it strikes If the reflected light enters your eyes, you see an image of the object The light first strikes the cornea The cornea is the clear outer covering of the eye After light passes through the cornea, it enters the pupil The pupil is an opening into the eye

Your pupils change size to let in more or less light Your pupils are small when there

is a lot of light They grow larger and let in more light as the amount of light around you decreases This change in your pupil’s size is caused by the iris The iris is the colored circle that surrounds the pupil It controls how much light enters the eye by changing the size of the pupil

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2SbOWZa 2SbOWZa 2SbOWZa

lens

cornea pupil

Light that moves into your

eye must be focused This is just

like light from a movie projector

that must be focused on a screen

The part of the eye that focuses

incoming light is the lens It is

located behind the pupil and

iris The lens focuses light on the

back of the eyeball Information

about the picture that forms is

sent to the brain The brain then

makes sense out of the picture

Quick Check

Main Idea How does reflected

light allow you to see?

Critical Thinking Why does

the size of a pupil change?

D Light entering the eye passes through the cornea, the

pupil, and the lens The light

is focused on the eyeball to form an image

How Light Affects Your Pupils

Predict Does the amount of light in a room affect your pupils? Write down your prediction

Observe Dim the classroom lights Look at your pupils in a mirror Make a sketch of what you see

Observe Turn on the classroom lights Again, look at your pupils

in the mirror Make a sketch of what you see

Compare How do your sketches differ?

Draw Conclusions What caused differences in your sketches? What does this show about the amount of light that enters your eyes?

359

EXPLAIN

Why can you see colors?

Have you ever seen a rainbow? If so, you probably saw bands of different colors This happens when white light is separated by an object called a prism (PRIZ•uhm) A prism

is a special lens that separates white light Drops of water in the sky can act like prisms and separate sunlight When this happens,

a rainbow forms A rainbow has seven different colors That is because white light

is made up of seven different colors of light When white light strikes an object, some colors of light are absorbed , or taken in Some colors of light are reflected If you look at the object, some of the reflected light enters your pupils You see the object

as the color of this reflected light.

Red, orange, yellow,

green, blue, indigo,

and violet are the

colored lights that

form white light

When light passes

Quick Check

Main Idea What happens when white light

passes through a prism?

Critical Thinking Why does a banana appear

Seeing Colors

White light that strikes a leaf is

made up of seven different colors

The leaf absorbs all of the colors

except for green Only green light

bounces off the leaf It is reflected to

your eyes You see the leaf as green

Something quite different happens

when the same white light strikes

a red flower Now the green light

is absorbed All of the colors are

absorbed except for red Only the

red light is reflected to your eyes

You see the flower as red.

Why is the leaf green but the flower red?

Clue: Look at the pictures of reflected light

Learn about seeing color

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Read a Diagram

361

EXPLAIN

Why do objects appear black

or white?

When white light hits a tar-covered road, all the colors of light are absorbed Almost no light is reflected This is why the road looks black When white light strikes a snowman, all the

colors of light are reflected No light is absorbed The snowman looks white.

What happens when you view a white object through a colored filter? Because a white object reflects all the colors of light, the object will look the same color as the filter If you shine

a red light on a white sheet of paper the paper will look red The filter only allows red light

to pass through it It absorbs all other colors

of light If you look at the same sheet of paper through a blue filter, it will look blue Only blue light can pass through the blue filter All the other colors of light are absorbed An object’s color is affected by the light shining on it.