Download 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
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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
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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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Reading Essentials