Essential Question: How do
images form by reflection?
Reflection
Two types of reflection
1. Regular or Specular
2. Diffuse
Law of Reflection –the angle of
incidence = the angle of reflection
Characteristics of Images in Plane Mirror
Characteristics of Images in Plane Mirror
1. Image located as far into the mirror as
object is in front of mirror.
2. Virtual Image
3. Erect Image
4. Same Size
5. Reverse left to right
6. Image form directly in front of object
Steps in drawing ray diagrams to locate
image in plane mirror.
1. Measure distance of object in
front of mirror.
5 cm
object
mirror
2. Draw in position of image
directly in line with object;same
distance behind mirror.
image
object
Can a person a position X see the
image?
image
X
object
Draw a line from X to the image.
image
X
object
If the line of sight crosses the
mirror then the image can be seen.
image
X
object
The red arrows show the actual path
of the light.
image
X
object
Reflection from Parabolic Mirror
Images formed by curved mirrors
have different characteristics than
those formed from flat mirrors.
Terminology of Curved Mirrors
Center of curvature (C)– the center of the
circle the mirror is a part of;twice the
distance as F
Principal
axis
C
F
Terminology of Curved Mirrors
Center of curvature (C)– the center of the
circle the mirror is a part of;twice the
distance as F/
Principal
axis
C
F
Focus(F) – the point where all rays parallel to
axis reflect to; half the distance to C
Terminology of Curved Mirrors
Center of curvature (C)– the center of the
circle the mirror is a part of;twice the
distance as F/
Principal
axis
C
F
Focus(F) – the point where all rays parallel to
axis reflect to; half the distance to C
Principal axis- the line passing through
C, and F and the center of mirror
Locating an image in a parabolic
mirror – must draw at least two
rays.
1ST -Draw a ray parallel to the
axis
C
F
Locating an image in a parabolic
mirror – must draw at least two
rays.
1st-Draw a ray parallel to the
axis
C
F
Locating an image in a parabolic
mirror – must draw at least two
rays.
1st-Draw a ray parallel to the
axis;it must reflect though F
C
F
2nd – Draw a ray through the focus
C
F
2nd – Draw a ray through the focus; it
will reflect parallel to the axis
C
F
Where the two rays cross is where the
image will form.
C
F
The light rays cross in front of mirror
so the image is real – it could be
projected!
C
F
The light rays cross in front of mirror
so the image is real – it could be
projected!
C
F
The image is inverted.
The light rays cross in front of mirror
so the image is real – it could be
projected!
C
F
The image is inverted.
The image is smaller than the object.
Will the Image always have these
same characteristics?
Lets move the object to a new
position closer to C.
C
F
Lets move the object to a new
position closer to C.
C
F
Now lets draw in the two rays.
C
F
Now lets draw in the two rays.
C
F
Now lets draw in the two rays.
C
F
Now lets draw in the two rays.
C
F
Now lets draw in the two rays.
C
F
Now lets draw in the two rays.
C
F
How are the images different?
C
C
F
F
What do you think will happen if
the object is placed at C?
C
F
What do you think will happen if
the object is placed at C?
C
F
Lets draw in the rays to see the
formation of the image
C
F
Lets draw in the rays to see the
formation of the image
C
F
Lets draw in the rays to see the
formation of the image
C
F
Lets draw in the rays to see the
formation of the image
C
F
Lets draw in the rays to see the
formation of the image
C
F
The size and type of image varies
with the object’s distance (do) from
the mirror.
If the object is so far
away that the rays
come in parallel, the
image will just be a
point a the focus.
If the object is beyond f the
image will always be real
and inverted. The size will
vary
If the object is right at f an
image will not form.
If the object is less than f
away, the image will be
enlarged, erect and virtual.
The mirror equation:
1 1 1
 
f do di
do
di
Magnification Equation:
h ' di
M  
h do
h’ is image height
h is object height
Images formed in Convex Mirrors:
Images formed in Convex Mirrors:
Images formed in Convex Mirrors:
Images are always virtual, erect
and smaller.
Large spherical mirrors have
spherical aberration which
causes the blurred images
Making the mirror parabolic
instead of spherical reduces
the spherical aberration