Light, Mirrors, and Lenses s.net

[Pages:41]Light, Mirrors,

Light waves can be absorbed, reflected, and transmitted by matter.

and Lenses

SECTION 1

Properties of Light

Main Idea A source of light

gives off light rays that travel

outward in all directions.

SECTION 2

Reflection and Mirrors

Main Idea When a light ray is reflected from a surface, the angle of incidence equals the angle of reflection.

SECTION 3

Refraction and Lenses

Main Idea A light ray changes direction when it moves from one material into another and changes speed.

SECTION 4

Using Mirrors and Lenses

Main Idea Lenses and mirrors are used to form images of objects that cannot be seen with the human eye.

Seeing the Light

This lighthouse at Pigeon Point, California, produces beams of light that can be seen for many miles. These intense light beams are formed in the same way as a flashlight beam. The key ingredient is a curved mirror that reflects the light from a bright source.

Science Journal Describe how you use mirrors and lenses during a typical day.

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Chad Ehlers/Index Stock

Start-Up Activities

Bending Light

Everything you see results from light waves entering your eyes. These light waves are either given off by objects, such as the Sun and lightbulbs, or reflected by objects, such as trees, books, and people. Lenses and mirrors can cause light to change direction and make objects seem larger or smaller.

1. Place two paper cups next to each other and put a penny in the bottom of each cup.

2. Fill one of the cups with water and observe how the penny looks.

3. Looking straight down at the cups, slide the cup with no water away from you just until you can no longer see the penny.

4. Pour water into this cup and observe what seems to happen to the penny.

5. Think Critically In your Science Journal, record your observations. Did adding water make the cup look deeper or shallower?

Light, Mirrors, and Lenses Make the following Foldable to help you understand the properties of and the relationship between light, mirrors, and lenses.

STEP 1 Fold a sheet of pape in half lengthwise. Make the back edge about 5 cm longer than the front edge.

STEP 2

Turn the paper so the fold is on the bottom. Then fold it into thirds.

STEP 3 Unfold and cut only the top layer along folds to make three tabs.

STEP 4 Label the Foldable as shown.

Light, Mirrors, and Lenses

Light

Mirrors

Lenses

Preview this chapter's content and activities at booko.

Summarize in a Table As you read the chapter, summarize the information you find about light, mirrors, lenses.

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Chad Ehlers/Index Stock

Learn It! Asking questions helps you to understand what

you read. As you read, think about the questions you'd like answered. Often you can find the answer in the next paragraph or section. Learn to ask good questions by asking who, what, when, where, why, and how.

Practice It! Read the following passage from Section 3.

Optical fibers are used most commonly in the communications industry. For example, television programs, computer information, and phone conversations can be coded into light signals. These signals can then be sent from one place to another using optical fibers. Because of total internal reflection, signals cannot leak from one fiber to another, causing interference. As a result, the signal is transmitted clearly.

-- from page 112

Here are some questions you might ask about this paragraph: ? How are optical fibers used by the communications industry? ? What type of signals are sent through optical fibers? ? Why are signals transmitted clearly in optical fibers?

Apply It! As you read the

chapter, look for answers to lesson headings that are in the form of questions.

96 A O CHAPTER 4 Light, Mirrors, and Lenses

Use this to focus on the main ideas as you read the chapter.

Before you read the chapter, respond to the statements below on your worksheet or on a numbered sheet of paper. ? Write an A if you agree with the statement. ? Write a D if you disagree with the statement.

Test yourself. Create questions and then read to find answers

to your questions.

After you read the chapter, look back to this page to see if you've changed your mind about any of the statements. ? If any of your answers changed, explain why. ? Change any false statements into true statements. ? Use your revised statements as a study guide.

Before You Read A or D

Statement

Print out a worksheet of this page at booko.

1 All objects give off light on their own.

2 You see an object when light rays travel from your eyes to the object.

3 The color of an object depends on the wavelengths of the light waves reflected from the object.

4 Light rays obey the law of reflection only if the reflecting surface is very smooth.

5 Light waves travel at the same speed in all materials.

6 A lens causes all light rays to pass through the focal point of the lens.

7 The image formed by a lens depends on how far the object is from the lens.

8 The purpose of the large concave mirror in a reflecting telescope is to magnify objects.

9 A laser beam contains a single wavelength of light.

After You Read A or D

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Properties of Light

Describe the wave nature of light.

Explain how light interacts with materials.

Determine why objects appear to have color.

Everything you see comes from information carried by light waves.

Review Vocabulary

electromagnetic waves: waves created by vibrating electric charges that can travel through space or through matter

New Vocabulary

light ray

?? medium

Figure 1 Light moves

away in all directions from a light source, just as ripples spread out on the surface of water.

What is light?

Drop a rock on the smooth surface of a pond and you'll see ripples spread outward from the spot where the rock struck. The rock produced a wave much like the one in Figure 1. A wave is a disturbance that carries energy through matter or space. The matter in this case is the water, and the energy originally comes from the impact of the rock. As the ripples spread out, they carry some of that energy.

Light is another type of wave that carries energy. A source of light such as the Sun or a lightbulb gives off light waves into space, just as the rock hitting the pond causes waves to form in the water. But while the water waves spread out only on the surface of the pond, light waves spread out in all directions from the light source. Figure 1 shows how light waves travel.

Sometimes, however, it is easier to think of light in a different way. A light ray is a narrow beam of light that travels in a straight line. You can think of a source of light as giving off, or emitting, a countless number of light rays that are traveling away from the source in all directions.

A source of light, such as a lightbulb, gives off light rays that travel away from the light source in all directions.

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Dick Thomas/Visuals Unlimited

Ripples on the surface of a pond are produced by an object hitting the water. The ripples spread out from the point of impact.

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