is10_sb_unit_d

Concave Mirrors
A concave mirror, also called a converging mirror, has a surface that
curves inward like a bowl (Figure 11.10). The image formed by a
concave mirror depends on how far the object is from the focal point of
the mirror. If the object is far away from the focal point, the reflected
rays form an inverted image as shown in Table 11.1. The closer the
object gets to the focal point, the larger the image becomes. If the object
is between the focal point and the mirror, like the bird in Figure 11.11,
the image becomes upright and enlarged. When the object is exactly at
the focal point, all rays that leave the object reverse direction at the
mirror and are reflected away from the mirror parallel to each other. In
this case, no image is formed.
F
Figure 11.10 Parallel light rays approaching a concave mirror.
Table 11.1 Ray Diagrams for Concave Mirrors
Distance of Object
from Mirror, d o
Object is more than
two focal lengths.
Object is between one
and two focal lengths.
Type of Image
Formed
Smaller than object,
inverted, real
Larger than object,
inverted, real
How the Image
Is Viewed
The mirror can project
an image on a screen
placed in front of the
mirror.
The mirror can project
an image on a screen
placed in front of the
mirror.
Ray Diagram
Object is at focal point. No image is formed. No image is formed. object
Object is between
mirror and focal point.
Larger than object,
upright, virtual
Viewer looks into the
mirror to see the
image.
object
image
Figure 11.11 A virtual image produced by a converging mirror.
The bird is between the focal point and the mirror so the virtual
image is larger than the real bird.
Ray diagrams model the behaviour of light in mirrors and lenses.
F
F
object
F
object
F
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