Reflection and Mirrors
Light Reflection and Mirrors Key Concepts • How does light reflect from smooth surfaces and rough surfaces? • What happens to light when it strikes a concave mirror? • Which types of mirrors can produce a virtual image?
whether you agree or disagree with them. Place an A in the Before column if you agree with the statement or a D if you disagree. After you’ve read this lesson, reread the statements to see if you have changed your mind. Before
Statement
After
3. Mirrors are the only surfaces that reflect light. 4. The image in a mirror is always right side up.
Reflection of Light Reflection is the bouncing of a wave off a surface. If you throw a tennis ball straight at a wall, it will bounce back to you. Where on the wall would you throw the ball so that a friend standing to your left could catch it? You would throw it toward a point on the wall halfway between you and your friend. Law of Reflection
Law of Reflection Visual Check
1. Solve If the angle of incidence is 40°, what is the angle of reflection?
Reading Check
2. Contrast How do the reflected and incident rays differ?
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Light
Light reflects a lot like a tennis Reflected ball bouncing off a wall. Straight ray arrows called rays show how light reflects, as seen in the figure. An Angle of imaginary line perpendicular to a reflection Normal reflecting surface is the normal. The light ray moving toward the Angle of incidence surface is the incident ray. The light ray moving away is the Incident reflected ray. Notice the angle ray formed where an incident ray meets a normal. This is the angle of incidence. A reflected ray forms an identical angle on the other side of the normal. This angle is the angle of reflection. According to the law of reflection, when a wave is reflected from a surface, the angle of reflection is equal to the angle of incidence. Reading Essentials
Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
Sticky Notes As you read, use sticky notes to mark information that you do not understand. Read the text carefully a second time. If you still need help, write a list of questions to ask your teacher.
What do you think? Read the two statements below and decide
Regular and Diffuse Reflection You see objects when light reflects off them into your eyes. Why can you see your reflection in smooth, shiny surfaces but not in a piece of paper or a painted wall? The law of reflection applies whether the surface is smooth or rough.
Shiny Surfaces Reflection of light from a smooth, shiny surface is called regular reflection. Look back at the figure on the previous page. The three incident rays and the three reflected rays are all parallel. You see a sharp image when parallel rays reflect rays reflect into your eyes.
Diffuse Reflection Scattered reflected rays
Visual Check
3. Confirm Does the law Tilted normals
of reflection apply to rough surfaces? Explain.
Rough Surfaces When light strikes an uneven surface, as in Parallel the figure at right, the angle of incident reflection still equals the angle rays of incidence at each point. However, different rays reflect in different directions. Reflection of light from a rough surface is called diffuse reflection.
Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
Mirrors Any surface that reflects light and forms an image is a mirror. The type of image depends on whether the reflecting surface is flat or curved. The image forms when light reflects off an object to a reflecting surface. The surface reflects the light back to your eye. Your brain knows that light travels in straight lines, so it understands this light as an image of the object.
Key Concept Check
4. Compare How does light reflect from smooth surfaces and rough surfaces?
Plane Mirrors The word plane means “flat,” so a plane mirror has a flat reflecting surface. The image a plane mirror forms is the same size as the object. However, it is a virtual image because no object is located at the place where the image appears. A virtual image is an image of an object that your brain perceives to be in a place where the object is not. Suppose you look at your image in a plane mirror. If you raise your right hand, your image raises its left hand. However, up and down are not reversed. The image you see in a plane mirror is not simply flipped around. Instead, you see an object as if you were viewing it from just behind the surface of the mirror.
Reading Essentials
Make a two-tab concept map book to compare the reflection of light on different types of surfaces. Light Reflection
Smooth Surface
Rough Surface
Light
329
Concave Mirrors
Visual Check
5. Relate How are the focal length and the focal point of a concave mirror related?
Not all mirrors are flat. A mirror that curves inward is called a concave mirror, like the mirror shown in the figure. A line perpendicular to the center of the mirror is the optical axis. The law of reflection determines Concave Mirror the direction of reflected rays in the figure at right. When rays Focal point parallel to the optical axis strike a Optical axis concave mirror, the reflected rays converge, or come together.
Focal Point Look at the figure. Notice the point where the rays converge. The point where light rays Focal length parallel to the optical axis converge after being reflected by a mirror or refracted by a lens is the focal point. You will learn about lenses in the next lesson. Imagine that a concave mirror is part of a hollow sphere. The focal point is halfway between the mirror and the center of the sphere. The distance along the optical axis from the mirror to the focal point is the focal length. The lesser the curve of a mirror, the longer its focal length. The position of an object compared to the focal point determines the type of image formed by a concave mirror.
6. Describe How does a concave mirror reflect light?
Types of Images A concave mirror can produce a real or a virtual image. The type of image a concave mirror forms depends on the object’s location relative to the focal point, as shown in the image at the top of the next page. The image is virtual if the object is between the focal point and the mirror. The image is real if the object is beyond the focal point. A real image is one that forms where rays converge. No image forms if the object is at the focal point.
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Light
Reading Essentials
Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
Key Concept Check
Look again at the figure of the concave mirror to understand how a flashlight works. Imagine all the arrows pointing in the opposite direction. The bulb is at the focal point. The concave mirror behind the bulb is the reflector. Light rays from the bulb strike the mirror and reflect as parallel rays.
Real and Virtual Images of Concave Mirrors An object outside the focal point produces a real, inverted image. The image appears smaller the farther the Focal point object is from the mirror. Focal point Real inverted image
Object
Object
Virtual upright image
An object inside the focal point produces a virtual, upright image.
Inverted Images Suppose you look at your reflection in the bowl of a shiny spoon. If your face is outside the spoon’s focal point, your image appears upside down, or inverted. Your image disappears when your face is at the focal point. When your face is inside the focal point, the image is upright.
Visual Check
7. Explain How do objects appear different inside and outside the focal point?
Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
Convex Mirrors Have you ever seen a large, round mirror high in the corner of a store? The mirror enables workers at the store to see places they cannot see with a plane mirror. A mirror that curves outward, like the back of a spoon, is called a convex mirror. Light rays diverge, or spread apart, after they strike the surface of a convex mirror. Your brain interprets these rays as coming from a smaller object behind the mirror. Therefore, a convex mirror always produces a virtual image that is upright and smaller than the object being reflected. As you have read, convex mirrors and plane mirrors form only virtual images. However, concave mirrors can form both virtual images and real images.
8. Apply Suppose you are standing 3 m from a concave mirror. The focal point is 2 m from the mirror. How will your image appear? (Circle your answer.) a. inverted image b. upright image c. no image Key Concept Check
9. Identify Which types of mirrors can form virtual images?
Reading Essentials
Light
331
Mini Glossary concave mirror: a mirror that curves inward
focal point: the point where light rays parallel to the optical
convex mirror: a mirror that curves outward, like the back of
axis converge after being reflected by a mirror or refracted by a lens
a spoon
diffuse reflection: reflection of light from a rough surface focal length: the distance along the optical axis from the mirror to the focal point
law of reflection: the law that states that when a wave is reflected from a surface, the angle of reflection is equal to the angle of incidence
regular reflection: reflection of light from a smooth, shiny surface
1. Review the terms and their definitions in the Mini Glossary. Write a sentence that explains how regular and diffuse reflection are related.
2. Use what you have learned about mirrors to fill in the blanks in the table below. Type of Mirror
Shape of Mirror
Type of Image(s) Produced
Plane Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
inside bowl of spoon outside curve of spoon
always virtual
3. During reflection, what is always true of the angles that the incident ray and the reflected ray form with the normal? What law describes this idea?
What do you think Reread the statements at the beginning of the lesson. Fill in the After column with an A if you agree with the statement or a D if you disagree. Did you change your mind?
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Light
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Log on to ConnectED.mcgraw-hill.com and access your textbook to find this lesson’s resources.
END OF LESSON
Reading Essentials
whether you agree or disagree with them. Place an A in the Before column if you agree with the statement or a D if you disagree. After you’ve read this lesson, reread the statements to see if you have changed your mind. Before
Statement
After
3. Mirrors are the only surfaces that reflect light. 4. The image in a mirror is always right side up.
Reflection of Light Reflection is the bouncing of a wave off a surface. If you throw a tennis ball straight at a wall, it will bounce back to you. Where on the wall would you throw the ball so that a friend standing to your left could catch it? You would throw it toward a point on the wall halfway between you and your friend. Law of Reflection
Law of Reflection Visual Check
1. Solve If the angle of incidence is 40°, what is the angle of reflection?
Reading Check
2. Contrast How do the reflected and incident rays differ?
328
Light
Light reflects a lot like a tennis Reflected ball bouncing off a wall. Straight ray arrows called rays show how light reflects, as seen in the figure. An Angle of imaginary line perpendicular to a reflection Normal reflecting surface is the normal. The light ray moving toward the Angle of incidence surface is the incident ray. The light ray moving away is the Incident reflected ray. Notice the angle ray formed where an incident ray meets a normal. This is the angle of incidence. A reflected ray forms an identical angle on the other side of the normal. This angle is the angle of reflection. According to the law of reflection, when a wave is reflected from a surface, the angle of reflection is equal to the angle of incidence. Reading Essentials
Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
Sticky Notes As you read, use sticky notes to mark information that you do not understand. Read the text carefully a second time. If you still need help, write a list of questions to ask your teacher.
What do you think? Read the two statements below and decide
Regular and Diffuse Reflection You see objects when light reflects off them into your eyes. Why can you see your reflection in smooth, shiny surfaces but not in a piece of paper or a painted wall? The law of reflection applies whether the surface is smooth or rough.
Shiny Surfaces Reflection of light from a smooth, shiny surface is called regular reflection. Look back at the figure on the previous page. The three incident rays and the three reflected rays are all parallel. You see a sharp image when parallel rays reflect rays reflect into your eyes.
Diffuse Reflection Scattered reflected rays
Visual Check
3. Confirm Does the law Tilted normals
of reflection apply to rough surfaces? Explain.
Rough Surfaces When light strikes an uneven surface, as in Parallel the figure at right, the angle of incident reflection still equals the angle rays of incidence at each point. However, different rays reflect in different directions. Reflection of light from a rough surface is called diffuse reflection.
Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
Mirrors Any surface that reflects light and forms an image is a mirror. The type of image depends on whether the reflecting surface is flat or curved. The image forms when light reflects off an object to a reflecting surface. The surface reflects the light back to your eye. Your brain knows that light travels in straight lines, so it understands this light as an image of the object.
Key Concept Check
4. Compare How does light reflect from smooth surfaces and rough surfaces?
Plane Mirrors The word plane means “flat,” so a plane mirror has a flat reflecting surface. The image a plane mirror forms is the same size as the object. However, it is a virtual image because no object is located at the place where the image appears. A virtual image is an image of an object that your brain perceives to be in a place where the object is not. Suppose you look at your image in a plane mirror. If you raise your right hand, your image raises its left hand. However, up and down are not reversed. The image you see in a plane mirror is not simply flipped around. Instead, you see an object as if you were viewing it from just behind the surface of the mirror.
Reading Essentials
Make a two-tab concept map book to compare the reflection of light on different types of surfaces. Light Reflection
Smooth Surface
Rough Surface
Light
329
Concave Mirrors
Visual Check
5. Relate How are the focal length and the focal point of a concave mirror related?
Not all mirrors are flat. A mirror that curves inward is called a concave mirror, like the mirror shown in the figure. A line perpendicular to the center of the mirror is the optical axis. The law of reflection determines Concave Mirror the direction of reflected rays in the figure at right. When rays Focal point parallel to the optical axis strike a Optical axis concave mirror, the reflected rays converge, or come together.
Focal Point Look at the figure. Notice the point where the rays converge. The point where light rays Focal length parallel to the optical axis converge after being reflected by a mirror or refracted by a lens is the focal point. You will learn about lenses in the next lesson. Imagine that a concave mirror is part of a hollow sphere. The focal point is halfway between the mirror and the center of the sphere. The distance along the optical axis from the mirror to the focal point is the focal length. The lesser the curve of a mirror, the longer its focal length. The position of an object compared to the focal point determines the type of image formed by a concave mirror.
6. Describe How does a concave mirror reflect light?
Types of Images A concave mirror can produce a real or a virtual image. The type of image a concave mirror forms depends on the object’s location relative to the focal point, as shown in the image at the top of the next page. The image is virtual if the object is between the focal point and the mirror. The image is real if the object is beyond the focal point. A real image is one that forms where rays converge. No image forms if the object is at the focal point.
330
Light
Reading Essentials
Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
Key Concept Check
Look again at the figure of the concave mirror to understand how a flashlight works. Imagine all the arrows pointing in the opposite direction. The bulb is at the focal point. The concave mirror behind the bulb is the reflector. Light rays from the bulb strike the mirror and reflect as parallel rays.
Real and Virtual Images of Concave Mirrors An object outside the focal point produces a real, inverted image. The image appears smaller the farther the Focal point object is from the mirror. Focal point Real inverted image
Object
Object
Virtual upright image
An object inside the focal point produces a virtual, upright image.
Inverted Images Suppose you look at your reflection in the bowl of a shiny spoon. If your face is outside the spoon’s focal point, your image appears upside down, or inverted. Your image disappears when your face is at the focal point. When your face is inside the focal point, the image is upright.
Visual Check
7. Explain How do objects appear different inside and outside the focal point?
Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
Convex Mirrors Have you ever seen a large, round mirror high in the corner of a store? The mirror enables workers at the store to see places they cannot see with a plane mirror. A mirror that curves outward, like the back of a spoon, is called a convex mirror. Light rays diverge, or spread apart, after they strike the surface of a convex mirror. Your brain interprets these rays as coming from a smaller object behind the mirror. Therefore, a convex mirror always produces a virtual image that is upright and smaller than the object being reflected. As you have read, convex mirrors and plane mirrors form only virtual images. However, concave mirrors can form both virtual images and real images.
8. Apply Suppose you are standing 3 m from a concave mirror. The focal point is 2 m from the mirror. How will your image appear? (Circle your answer.) a. inverted image b. upright image c. no image Key Concept Check
9. Identify Which types of mirrors can form virtual images?
Reading Essentials
Light
331
Mini Glossary concave mirror: a mirror that curves inward
focal point: the point where light rays parallel to the optical
convex mirror: a mirror that curves outward, like the back of
axis converge after being reflected by a mirror or refracted by a lens
a spoon
diffuse reflection: reflection of light from a rough surface focal length: the distance along the optical axis from the mirror to the focal point
law of reflection: the law that states that when a wave is reflected from a surface, the angle of reflection is equal to the angle of incidence
regular reflection: reflection of light from a smooth, shiny surface
1. Review the terms and their definitions in the Mini Glossary. Write a sentence that explains how regular and diffuse reflection are related.
2. Use what you have learned about mirrors to fill in the blanks in the table below. Type of Mirror
Shape of Mirror
Type of Image(s) Produced
Plane Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
inside bowl of spoon outside curve of spoon
always virtual
3. During reflection, what is always true of the angles that the incident ray and the reflected ray form with the normal? What law describes this idea?
What do you think Reread the statements at the beginning of the lesson. Fill in the After column with an A if you agree with the statement or a D if you disagree. Did you change your mind?
332
Light
Connect ED
Log on to ConnectED.mcgraw-hill.com and access your textbook to find this lesson’s resources.
END OF LESSON
Reading Essentials
