Chapter 18
Mirrors and Lenses
18.1 Mirrors



A. Objects and Images in Plane Mirrors.
B. Concave Mirrors.
C. Convex Mirrors
A. Objects and images in Plane Mirrors.

1. A plane mirror is a flat, smooth
surface from which light is
reflected by regular reflection.
a. An object is a source of
spreading or diverging light rays.
 b. The point at which the source
appears to be coming from is
called the image.
 c. A virtual image is one where the
rays do not actually converge.

B. Concave mirrors
1. A concave or “caved in” mirror
reflects light from its inner surface.
 2. Real vs. Virtual images.
 3. Real images formed by concave
mirrors.
 4. Lens/Mirror equation.

1/f
= 1/di + 1/do

5. Magnification
m
= hi/ho
m
= -di/do
Describing a real image
 Virtual images formed by concave mirrors
 Image defects in concave mirrors

 Spherical
aberration
C. Convex Mirrors



A convex mirror is a spherical mirror
that reflects light from its outer
surface.
Focal length of a convex mirror is
negative
All images formed are virtual images.
PSS

1. Choose a scale for your drawing that is
approximately the width of your paper.
Locate the image and object locations relative to the
mirror.
 Choose a scale such that the larger distance is 15 to
20 cm on your paper.
 Let 1 cm on the paper represent 1, 2, 4, 5, or 10
actual centimeters.


Draw the principle axis

Draw a vertical line where the principal axis
touches the mirror. If the focal point is known,
indicate its position on the principal axis.
C
f

Draw the object and label its top O1
O1
C

f
Choose a scale for the object that is different
than that of the overall drawing because
otherwise it may be too small to be seen.

Draw ray 1, the parallel ray. Ray 1 is parallel to
the principal axis. All parallel ray to the principal
axis are reflected through the focal point.
O1
Ray 1
C
f

Draw ray 2, the focus ray. It passes through the
focal point, f, on its way to the mirror and is
reflected back parallel to the principal axis.
O1
Ray 1
Ray 2
C
f

The image is located where the two rays
intersect after reflection. Draw a vertical line
from I1 to the principal axis to represent the
image.
O1
Ray 1
Object
Ray 2
Image
C
I1
f

O
A third ray may be drawn from the objects top to the
center of the mirror which will reflect at the same angle
at which it is incident.
1
Ray 1
Ray 3
Object
Ray 2
Image
C
I
1
f
Homework
 Chapter
18 practice problems 1 – 8.