3 13 light (physical science)

Main Idea and Supporting Details Traveling light rays react differently when they reach different materials.. Extended Vocabulary lens opaque rainbow shadow spectrum translucent transp

Scott Foresman Science 3.13

Nonfi ction Main Idea and

Supporting Details

• Captions

• Diagrams

• Text Boxes

• Glossary

Energy

ISBN 0-328-13846-0 ì<(sk$m)=bdiegd< +^-Ä-U-Ä-U

Scott Foresman Science 3.13

Nonfi ction Main Idea and

Supporting Details

• Captions

• Diagrams

• Text Boxes

• Glossary

Energy

ISBN 0-328-13846-0 ì<(sk$m)=bdiegd< +^-Ä-U-Ä-U

1 What is our most important natural

light source?

2 Explain how light travels.

3 A mirror and a leaf refl ect light

differently Why?

have read about ways in which people use the refraction of light in their everyday lives Write to explain some ways in which refraction is used Use examples from the book

5 Main Idea and Supporting Details Traveling light rays react

differently when they reach different materials What details from the book support this idea?

What did you learn?

Extended Vocabulary

lens opaque rainbow shadow spectrum translucent transparent white light

Vocabulary

absorb

electric charge

electric circuit

electric current

kinetic energy

potential energy

refl ect

refract

thermal energy

Picture Credits

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The publisher deeply regrets any omission and pledges to correct errors called to its attention in subsequent editions.

Photo locators denoted as follows: Top (T), Center (C), Bottom (B), Left (L), Right (R), Background (Bkgd).

Opener: John Lund/Corbis; 5 (TL) Getty Images; 6 Craig Tuttle/Corbis; 9 (B) Robert Holmes/Corbis;

14 Science Museum, London/DK Images; 17 John Lund/Corbis; 20 JS Productions/Corbis; 23 Craig Tuttle/Corbis.

Scott Foresman/Dorling Kindersley would also like to thank: 9 (TR) NASA/DK Images; 15 (BR) Stephen Oliver/DK Images.

Unless otherwise acknowledged, all photographs are the copyright © of Dorling Kindersley, a division of Pearson

ISBN: 0-328-13846-0

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3 4 5 6 7 8 9 10 V010 13 12 11 10 09 08 07 06 05

by Marianne Lenihan

We live in a world fi lled with energy Light

is a form of energy Objects such as the Moon

refl ect light Light will also refract when it

passes through water

Energy comes in many different forms other

than light Potential energy has the ability to

change to another form in order to do work

or cause a change When we burn

fuels, we release their potential energy

Kinetic energy is the energy of

motion Whenever we begin to walk

or run, potential energy changes

to kinetic energy

Thermal energy is the total

energy of all the particles in

matter The thermal energy in a

heated room is what warms us!

2

What You Already Know

A swing changes potential energy

to kinetic energy, and kinetic energy

to potential energy.

All matter is made up of small particles that have electric charges

An electric charge is a tiny amount

of energy An electric charge can move from one place to another as

an electric current The path that a controlled electric current fl ows through is called an electric circuit

Light comes to us from the Sun and from sources such as electricity We use light in many different ways Light has many fascinating qualities! Keep reading

to fi nd out more about light

3

light bulb

Sources of Light

Daylight is the result of Earth receiving light

from the Sun as it turns on its axis As Earth

rotates, part of it enters into darkness, and

another part comes into daylight Most of Earth

experiences both day and night every 24 hours

The Sun is not our only source of natural

light The nighttime stars shine brightly The

planets you see in the night sky, such as Venus,

shine also But the light the planets give off is

not their own Like the Moon, Venus refl ects

the Sun’s light

Stars are a source

of natural light

The Sun is the star nearest to Earth.

4

Lightning is a form of electricity It creates huge amounts of light Firefl ies and some kinds of fi sh also make natural light

The Sun will always be our most important source of light But artifi cial light gives us light when it’s dark outside For the past century,

we have been using electric-powered lights in our homes and schools, and on city streets

Before electricity was used for light, people used campfi res, oil and gas lamps,

and wax candles These types

of light sources are still used today However, electric-powered lights are our main source

of artifi cial light

Light travels at more than 186,000 miles per second

Light from the Sun takes about eight minutes to reach Earth.

5

Flashlights use battery-powered electricity to provide artifi cial light.

Traveling Light

Light travels very fast—much faster than

sound That’s why you see a fl ash of lightning

before you hear the sound of thunder, even

though both happen at exactly the same time

Light travels in straight lines A fl ashlight’s

beam shows this If you shine a fl ashlight on a

wall, you can mark where its beam of light hits

The distance from the mark back to the fl ashlight

is always a straight line

Light rays travel in a straight line from the Sun to Earth.

6

Traveling light rays react differently when they reach different types of materials Transparent materials allow all light rays to travel through them Translucent materials allow some light to shine through them Frosted glass, stained-glass windows, and dark sunglasses are translucent Opaque

materials, such as doors, walls, and our bodies, block out all light rays Opaque materials absorb and refl ect light

Does light pass through?

Colored water lets light rays pass through easily Milky water allows only some rays to pass through, while ink blocks them completely.

colored water (transparent)

milky water (translucent)

ink (opaque)

fl ashlight

7

Light and Shadow

Light rays travel from the Sun to Earth When

they reach an opaque object on Earth’s surface,

they are unable to pass through it This causes a

dark area, or shadow, to form on a surface on the

other side of the object The shadow takes the

same form as the object

Shadows change length throughout the day

They are shortest at noon Shadows get longer

as the Sun appears to move lower in the sky

Shadows such as this one are caused by shining

a bright light on an opaque object in front of a

background surface.

The most amazing shadow of all is seen during a solar eclipse

A solar eclipse is when the Moon passes

between the Sun and Earth This causes the Moon’s shadow to fall

on Earth’s surface

Shadows have been used for centuries to tell time A sundial is

a kind of clock It tells time using a shadow created by the Sun Obviously, sundials can’t measure the time at night!

9

This sundial is using the shadow cast by the Sun to measure the approximate time of day.

During a solar eclipse, the Moon casts its shadow on Earth’s surface.

Bouncing Light

Long ago, people thought that their eyes sent

out beams of light to the objects they saw around

them But people have shown that idea to be

false We now know that light rays bounce off

objects and enter our eyes

When light bounces off an object it is called

refl ected light Light rays refl ect differently off

smooth and rough surfaces Suppose you shine a

fl ashlight on the surface of a smooth mirror The

mirror refl ects the light in only one direction

10

Light bounces off mirrors

in only one direction.

Now, think about what would happen if you shined a fl ashlight on a leaf The leaf’s rough, uneven surface would scatter the light in all directions These scattered, refl ected light rays allow you to see the leaf from all sides

When light rays bounce off an object, most of the light is refl ected, but not all Some light is absorbed All objects, no matter how transparent, translucent, or opaque they are, absorb some light

11

How We See

We can see objects that are not light sources because light rays bounce off the objects and enter our eyes.

some light enters the eye

light source

plant refl ects light

light rays strike plant

Refl ections

Refl ections are formed by shiny materials,

such as glass mirrors and smooth water surfaces

Most metals refl ect the light that falls on them

Glass is not a metal However, it is usually

very fl at and smooth, like most metals Since

glass does not refl ect light rays well, how are

glass mirrors able to refl ect our image?

Mirrors are made by putting metal sheeting

behind a piece of glass The glass protects the

metal It also makes a smooth surface It is

the metal that refl ects our image back to us,

not the glass

Not all mirrors are made by humans A lake’s smooth, calm surface refl ects light rays very well

12

Mirrors can be used in many different ways

We can use them to see our appearance Mirrors can also help us stay safe Bicycle riders, car drivers, and other vehicle operators use mirrors to help them see while they are driving or riding Finally, mirrors can be used to send fl ashes of light over long distances This is a form of communication

Curved Surfaces

Have you ever looked at your refl ection in a spoon? The way the front of a spoon is curved can make your image appear larger and upside down The curve of the back

of the spoon can make your image appear smaller.

13

Bending Light

You already know that light moves through air

at an amazing speed When light travels through

other materials, such as water or glass, its speed

decreases The slowing down of light rays causes

them to change direction

Refraction is the name given to the slowing

down of light rays Because of the way that light

gets refracted through water, underwater objects

appear larger than they actually are Refraction

also causes our skin to absorb more of the

Sun’s heat energy while we’re in the water

That makes it very important to wear

sunscreen while swimming!

14

A light ray changes direction as it enters and leaves

a glass block.

We can fi nd many examples

of refraction in our daily lives

A spoon placed at an angle in a glass of water appears bent A pencil seen through a water-fi lled jar may appear to be broken

Lenses are used in eyeglasses, microscopes, telescopes, and magnifying glasses By using refraction, these lenses help people see better

15

Lenses

A lens is a specially shaped piece of glass or plastic It refracts light in a precise way.

A concave lens spreads light rays apart, which makes objects appear smaller than normal.

A convex lens focuses, or brings

to a point, the light rays of an object that is far away.

This pen placed

in a glass of water appears

to be broken.

Using Refraction

We use refraction created by lenses every day

for many different things Lenses can be used to

make objects that are far away look larger They

can also correct poor eyesight and focus light

rays into a very strong beam

People are born with two very important

lenses Each eye contains a lens The lens is

located just behind the pupil of each eye

The pupil is the black dot located in the

very middle of each eye

16

A magnifying glass is a type of

convex lens It can make objects

such as stamps appear much

larger than they actually are.

As we move our eyes from near to distant objects, special muscles attached to the lenses pull the lenses into different shapes By changing shapes, the lenses allow us to focus clearly on objects both near and far As people get older, their eyes’ lenses can change shape This can cause their vision to blur We can wear contact lenses or eyeglasses to correct our eyesight

A camera works a lot like our eyes do A convex lens uses light coming into the camera

to help create a clear, focused picture or image

This lighthouse light uses a specially shaped lens to create

a very strong beam

of light.

17

Splitting Light

Have you ever wondered what white light

is? Sunlight and light from an electric light bulb

seem to be colorless We call these two kinds of

light white light

White light is a mixture of many different

colors of light Those colors become separated

when white light passes through a prism A prism

is a triangular, transparent block Light passing

through a prism forms a band of colors called

a spectrum

18

This prism is splitting white light into a spectrum Notice all the different colors of light.

An object’s color tells us which color it refl ects Grass is green because that is the only color it refl ects The grass absorbs the other colors in the spectrum If an object appears red,

it is because it is absorbing every color except red The red rays are refl ected off the object

Most of the light that you see each day is white light However, not all light is white light

Red, green, and blue light only give off those colors Light can be any color found in the color spectrum!

19

This tea set’s different colors indicate which colors are being absorbed and which are being refl ected.

Rainbow Colors

You can see a rainbow because raindrops act

like tiny prisms White light enters a droplet of

water The water bends, or refracts, each color

in the light differently Then the light passes out

through the droplet But it no longer appears

as white light Instead, the light is split into

its colors

Rainbows occur most often after

rainfall or when there is fog That

is when a lot of water hangs

in the air That water

creates rainbows

20

To view a rainbow, you must have your back to the Sun.

Curved bands

of colored light are produced when a rainbow forms The sharpest rainbows are called primary rainbows They show the full spectrum of colors The colors in

a primary rainbow are: violet, indigo, blue, green, yellow, orange, and red People are able

to see these colors

21

How a Rainbow Forms

Light from the Sun passes through raindrops

in the air and gets refracted The refraction causes rainbows to form

sunlight

raindrop spectrum

Light in Our Lives

The Sun gives us daylight It provides our

planet with energy Light makes plants grow

Light makes it possible for people and animals

to live on Earth Stars and the Moon’s refl ected

light brighten the night sky

Natural light does much more than give us

day and night It allows us to see different colors,

refl ections, and shadows Light rays refl ect and

refract These properties are used in many

light-based inventions Our lives are made

happier, healthier, and safer with lighthouse

lights, mirrors, eyeglasses, and other inventions

It’s very easy for us to take light for granted

After all, the Sun appears to rise every day

We fl ip a switch and our homes, offi ces, and

streets are lit by electric-powered lights So it’s

important to remember that light is one of our

most important resources Without light, we

would not be here The universe would be

left in the dark