4/21/2015
Unit 11 Lesson 3 Mirrors and Lenses
Mirror Image
How do mirrors form images?
• Light waves travel from their source in all
directions and in a straight line.
• If a light wave hits an object, it may be reflected,
or it may bounce off the object.
Unit 11 Lesson 3 Mirrors and Lenses
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Unit 11 Lesson 3 Mirrors and Lenses
How do mirrors form images?
• A very smooth surface, such as a mirror, reflects
light in a uniform way.
• Most objects have rough surfaces that reflect light
in many different directions.
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Unit 11 Lesson 3 Mirrors and Lenses
How do mirrors form images?
• How does this ray diagram illustrate the law of
reflection?
• As light hits a mirror, an imaginary line, called the
normal, is perpendicular to the mirror’s surface.
• The angle that hits the surface is equal to the
angle at which the light is reflected. This is called
the law of reflection.
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Unit 11 Lesson 3 Mirrors and Lenses
Copyright © Houghton Mifflin Harcourt Publishing Company
Unit 11 Lesson 3 Mirrors and Lenses
How do mirrors form images?
How do mirrors form images?
• Most mirrors are plane mirrors; they have a flat
surface.
• When you see reflected light, your brain thinks
light has traveled in a straight line from behind
the mirror.
• The reflection in a plane mirror is right side up,
but reversed left to right.
• The reflected image will appear to be the same
size as the original object. The reflected image will
also appear to be the same distance behind the
mirror as the original object is in front of the
mirror.
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• A virtual image is an image that appears to
come from a place that the light does not actually
come from.
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4/21/2015
Unit 11 Lesson 3 Mirrors and Lenses
Unit 11 Lesson 3 Mirrors and Lenses
How do mirrors form images?
How do mirrors form images?
• A concave mirror is curved inward like the bowl
of a spoon.
• If a light source were held at the focal point, the
mirror would reflect parallel rays of light.
• Concave mirrors cause parallel light waves to
converge, or come together.
• Concave mirrors are useful for producing beams
of light and magnifying objects.
• Parallel light rays shining toward a concave mirror
converge at a point called the focal point.
• All images are formed where two or more rays
from the same location on an object converge.
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Unit 11 Lesson 3 Mirrors and Lenses
Copyright © Houghton Mifflin Harcourt Publishing Company
Unit 11 Lesson 3 Mirrors and Lenses
How do mirrors form images?
How do mirrors form images?
• Concave mirrors can form either virtual images or
real images.
• How does the distance of an object from a
concave mirror affect the type of image formed by
the mirror?
• A real image is formed where light from an
object converges.
• A real image can be projected onto a screen. A
virtual image cannot.
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Unit 11 Lesson 3 Mirrors and Lenses
Copyright © Houghton Mifflin Harcourt Publishing Company
Unit 11 Lesson 3 Mirrors and Lenses
How do mirrors form images?
How do mirrors form images?
• A convex mirror curves outward like the back of a
spoon.
• All images formed by a convex mirror are virtual,
right side up, and small.
• Convex mirrors cause a beam of light to diverge,
or spread apart as if it came from a focal point
behind the mirror.
• Convex mirrors are useful because they make
small images of large areas.
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• They are used for security in stores and factories.
Many cars, buses, and trucks use convex side
mirrors so the driver can see more of the
surrounding area.
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4/21/2015
Unit 11 Lesson 3 Mirrors and Lenses
Under a Lens
Unit 11 Lesson 3 Mirrors and Lenses
How do lenses form images?
How do lenses form images?
• A lens is a clear optical tool that refracts light.
• Refraction occurs when a light wave changes
speed as it passes from one medium to another.
• Light from an object passes through a lens to
form a real or virtual image.
• The type of image depends on the shape of the
lens and how close the object is to the lens.
• The change in speed makes the light waves bend
and either converge or diverge, depending on the
lens.
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Unit 11 Lesson 3 Mirrors and Lenses
How do lenses form images?
• A converging, or convex, lens is thicker at the
center than at the edges. It is often convex on
both sides.
• Parallel rays of light converge at a focal point after
they pass through a convex lens.
• The distance between the lens and focal point is
called the focal length.
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Unit 11 Lesson 3 Mirrors and Lenses
How do lenses form images?
• A diverging, or concave, lens is thinner at the
center than at the edges.
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Unit 11 Lesson 3 Mirrors and Lenses
How do lenses form images?
• Convex lenses are used to magnify or focus light.
• They are used in magnifying glasses, telescopes,
microscopes, binoculars, cameras, and projectors.
• Convex lenses are used in eyeglasses to correct
for farsightedness.
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Unit 11 Lesson 3 Mirrors and Lenses
How do lenses form images?
• The image formed by a concave lens is virtual,
right side up, and smaller than the object.
• Light that passes through a concave lens is
refracted outward as if from the focal point.
• Because they are refracted away from each other,
parallel light waves passing through a concave
lens do not meet.
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4/21/2015
Unit 11 Lesson 3 Mirrors and Lenses
How do lenses form images?
• In concave lenses, the distance between the
object and the lens does not make a difference in
the type of image that is formed.
• Diverging lenses are used to spread light, often in
combination with other lenses in telescopes and
binoculars, and to correct for nearsightedness.
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