Images Formed by Lenses
When light rays from an object pass through a lens, an image of
the object is formed. The type of image depends on the lens and, for
convex lenses, on the distance between the lens and the object.
SIMULATION
CLASSZONE.COM
Work with convex and
concave lenses to form
images.
Notice the distance between the penguin and the lens in the
illustration on page 554. The distance is measured in terms of a
focal length, which is the distance from the center of the lens to
the lens’s focal point. The penguin is more than two focal lengths
from the camera lens, which means the image formed is upside
down and smaller.
If the penguin were between one and two focal lengths away from
a convex lens, the image formed would be upside down and larger.
Overhead projectors form this type of image, which is then turned
right side up by a mirror and projected onto a screen for viewing.
Finally, if an object is less than one focal length from a
convex lens, it will appear right side up and larger. In order to
enlarge an object so that you can see details, you hold a magnifying lens close to the object. In the photograph, you see a
face enlarged by a magnifying lens. The boy’s face is less than
one focal length from the lens.
If you look at an object through a concave lens, you’ll see
an image of the object that is right side up and smaller than
the object normally appears. In the case of concave lenses, the
distance between the object and the lens does not make a difference in the type of image that is formed. In the next section
you’ll see how the characteristics of the images formed by different
lenses play a role in complex optical tools.
When will an image formed by a convex lens be upside down?
KEY CONCEPTS
CRITICAL THINKING
1. What quality of a material
affects how much it refracts
light?
4. Infer You look through a lens
and see an image of a building
upside down. What type of
lens are you looking through?
2. How does the curve in a lens
cause it to refract light differently from a flat piece of glass?
3. How does a camera lens form
an image?
5. Make a Model Draw the
path of a light ray moving at
an angle from air into water.
Write a caption to explain
the process.
CHALLENGE
6. Study the diagram on the
opposite page. Describe the
light rays that would pass
through the labeled focal
point. Where are they coming
from, and how are they related
to each other?
Chapter 16: Light and Optics 555