5.2 Using Mirrors to Form Images
•  All mirrors reflect light according to
the law of reflection.
•  A flat smooth mirror is called a plane
mirror.
w  The mirror on the wall, in your
bathroom, is probably a plane mirror.
•  The “object” is the original source of
light, and the “image” is where the
light converges (real image) or
where the light appears to originate
(virtual image). See next slide
•  A plane mirror produces virtual
images.
See page 182
(c) McGraw Hill Ryerson 2007
Plane Mirrors
•  Plane mirrors form an image that is upright and
appears to be as far behind the mirror as the object is
in front of it.
•  Left and right appear to be reversed in a plane mirror.
See pages 183 - 184
(c) McGraw Hill Ryerson 2007
Concave Mirrors
•  A concave mirror is a mirror that
curves inward.
•  Light reflecting off a concave mirror
meet at a single point called the focal
point.
w  Light rays that come together are called
converging rays.
w  Light rays that move apart are called
diverging rays.
•  The dotted line intersecting the
middle of the mirror is called the
“principal axis”
•  The distance from the mirror to the
focal point is called the “focal length”
See page 185
(c) McGraw Hill Ryerson 2007
Concave Mirrors
•  The image formed by a
concave mirror depends on
the location of the object (see
A, B C). In A and B a real image
is formed (converging light
rays), while in C a virtual
image is formed (diverging
rays).
•  When trying to determine the
location of an image a
minimum of two light rays are
required.
See page 185
(c) McGraw Hill Ryerson 2007
Concave Mirrors
•  Two things to remember about light rays and
spherical mirrors:
w  1) a parallel light ray will reflect through the focal point or a
light ray first traveling through the focal point will reflect
parallel
w  2)Law of reflection. The angle of incidence equals the angle
of reflection
•  Flashlights, car headlights, and telescopes, are a few
applications of concave mirrors.
•  It is actually a parabolic mirror that is used in
telescopes. Spherical mirrors suffer from a problem
called “spherical aberration”. You can look this term
up if your interested.
See page 185
(c) McGraw Hill Ryerson 2007
Convex Mirrors
• 
• 
• 
A convex mirror is a mirror that
curves outwards.
Reflected rays from a convex
mirror diverge and do not meet.
The image formed by a convex
mirror have two characteristics:
w  The images are always virtual.
w  Objects appear to be smaller than
they are.
w  More objects can be seen in a convex
mirror than in a plane mirror.
Convex mirrors are used in
stores as security mirrors
See page 186
(c) McGraw Hill Ryerson 2007
Convex Mirrors
• 
• 
The ray diagram on right,
shows how the image is
formed by a convex mirror.
The rays reflect and
diverge, hence the image
is virtual.
object
image
F
•  The reflected rays are projected back (dotted lines) to find
the intersection point.
•  The three most convenient rays to use are: 1) a parallel
ray (black) reflects and projects back through the focal
point, and 2) a ray (blue) reflected of the centre of the
mirror obeys the law of reflection (as all rays do).3) A ray
(red) in line with the focal point will reflect back parallel.