1. Unit 3 Lesson 3 Mirrors and Lenses
Copyright © Houghton Mifflin Harcourt Publishing Company

2. Mirror Image How do mirrors form images?
Unit 3 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.
Most objects have rough surfaces that reflect light in many different directions.
Copyright © Houghton Mifflin Harcourt Publishing Company

3. How do mirrors form images?
Unit 3 Lesson 3 Mirrors and Lenses
How do mirrors form images?
A very smooth surface, such as a mirror, reflects light in a uniform way.
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.
Copyright © Houghton Mifflin Harcourt Publishing Company

4. How do mirrors form images?
Unit 3 Lesson 3 Mirrors and Lenses
How do mirrors form images?
How does this ray diagram illustrate the law of reflection?
Copyright © Houghton Mifflin Harcourt Publishing Company

5. How do mirrors form images?
Unit 3 Lesson 3 Mirrors and Lenses
How do mirrors form images?
Most mirrors are plane mirrors; they have a flat surface.
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.
Copyright © Houghton Mifflin Harcourt Publishing Company

6. How do mirrors form images?
Unit 3 Lesson 3 Mirrors and Lenses
How do mirrors form images?
When you see reflected light, your brain thinks light has traveled in a straight line from behind the mirror.
A virtual image is an image that appears to come from a place that the light does not actually come from.
Copyright © Houghton Mifflin Harcourt Publishing Company

7. How do mirrors form images?
Unit 3 Lesson 3 Mirrors and Lenses
How do mirrors form images?
A concave mirror is curved inward like the bowl of a spoon.
Concave mirrors cause parallel light waves to converge, or come together.
Parallel light rays shining toward a concave mirror converge at a point called the focal point.
Copyright © Houghton Mifflin Harcourt Publishing Company

8. How do mirrors form images?
Unit 3 Lesson 3 Mirrors and Lenses
How do mirrors form images?
If a light source were held at the focal point, the mirror would reflect parallel rays of light.
Concave mirrors are useful for producing beams of light and magnifying objects.
All images are formed where two or more rays from the same location on an object converge.
Copyright © Houghton Mifflin Harcourt Publishing Company

9. How do mirrors form images?
Unit 3 Lesson 3 Mirrors and Lenses
How do mirrors form images?
Concave mirrors can form either virtual images or real images.
A real image is formed where light from an object converges.
A real image can be projected onto a screen. A virtual image cannot.
Copyright © Houghton Mifflin Harcourt Publishing Company

10. How do mirrors form images?
Unit 3 Lesson 3 Mirrors and Lenses
How do mirrors form images?
How does the distance of an object from a concave mirror affect the type of image formed by the mirror?
Copyright © Houghton Mifflin Harcourt Publishing Company

11. How do mirrors form images?
Unit 3 Lesson 3 Mirrors and Lenses
How do mirrors form images?
A convex mirror curves outward like the back of a spoon.
Convex mirrors cause a beam of light to diverge, or spread apart as if it came from a focal point behind the mirror.
Copyright © Houghton Mifflin Harcourt Publishing Company

12. How do mirrors form images?
Unit 3 Lesson 3 Mirrors and Lenses
How do mirrors form images?
All images formed by a convex mirror are virtual, right side up, and small.
Convex mirrors are useful because they make small images of large areas.
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.
Copyright © Houghton Mifflin Harcourt Publishing Company

13. Under a Lens How do lenses form images?
Unit 3 Lesson 3 Mirrors and Lenses
Under a Lens
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.
The change in speed makes the light waves bend and either converge or diverge, depending on the lens.
Copyright © Houghton Mifflin Harcourt Publishing Company

14. How do lenses form images?
Unit 3 Lesson 3 Mirrors and Lenses
How do lenses form images?
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.
Copyright © Houghton Mifflin Harcourt Publishing Company

15. How do lenses form images?
Unit 3 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.
Copyright © Houghton Mifflin Harcourt Publishing Company

16. How do lenses form images?
Unit 3 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.
Copyright © Houghton Mifflin Harcourt Publishing Company

17. How do lenses form images?
Unit 3 Lesson 3 Mirrors and Lenses
How do lenses form images?
A diverging, or concave, lens is thinner at the center than at the edges.
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.
Copyright © Houghton Mifflin Harcourt Publishing Company

18. How do lenses form images?
Unit 3 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.
Copyright © Houghton Mifflin Harcourt Publishing Company

19. How do lenses form images?
Unit 3 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.
Copyright © Houghton Mifflin Harcourt Publishing Company