2. air water As light reaches the boundary between two media,
its energy is partially reflected back and
partially transmitted into the new medium.
The amount that is reflected
depends on the types of materials and
the angle of incident rays.
air
water

3. Laws of Reflection First Law Second Law The angle of incidence, i, is
equal to the angle of reflection, r. n i r
Second Law
The incident and reflected rays,
and the normal, are coplanar.

4. Images formed by mirrors and lenses
may be classified as real or virtual.
Real Image
formed by actual rays of converging light
Virtual Image
not formed by actual rays of converging
light, but from where the rays of light
appear to come (diverging light rays)

5. Plane Mirror Images 1. virtual 2. upright 3. same size as object
Images formed by plane mirrors are always:
1. virtual
(virtual images are always behind mirrors)
2. upright
(virtual images are always upright)
3. same size as object
(if the image is larger or smaller, the mirror isn’t flat)
4. front and back are reversed
(some say “left and right”)
5. located as far behind the mirror
as the object is in front

7. Click here and here to view simulations
of light rays reflecting from a plane mirror.
View reflection from two plane mirrors
here and here.
Play a game here to test your skill.

8. Curved Mirrors Terminology center of curvature - C; the
center of the original sphere
radius of curvature - r;
distance from center of curvature to the mirror
vertex - V; the center of the mirror
principal axis - a line through C and V
principal focus - F; the point on the
principal axis where light rays parallel
and close to the principal axis converge;
or from where they appear to diverge
focal length - f; distance from V to F

9. Ray Diagrams Concave (Converging) Mirrors
rays parallel and close to the principal
axis reflect through the focus
2. rays passing through the focus reflect
parallel to the principal axis
3. rays passing through the center of
curvature reflect straight back along
the incident path
C F

10. Convex (Diverging) Mirrors
1. rays parallel and close to the principal
axis reflect away from the focus
2. rays heading toward the principal focus
reflect parallel to the principal axis
3. rays heading toward the center of
curvature reflect straight back along
the incident path
F C

11. Click here to view these three rays that are important in the formation of images in concave (converging) and convex (diverging) mirrors.
Also view reflection
from curved mirrors
here, here,and here.

12. di/do = si/so 1/f = 1/do + 1/di Mirror Equation Magnification
Diverging rays must be extended as dotted lines
behind the mirror in order to locate some images.
Mirror Equation
Magnification
di/do = si/so
1/f = 1/do + 1/di
f = focal length; positive for converging
mirrors, negative for diverging mirrors
do = object distance; usually positive
di = image distance; can be positive or negative
so = object size (height)
si = image size (height)

13. Images formed by concave (converging) mirrors may be:
1. real, virtual, or non-existent
2. upright or inverted
3. reduced, enlarged, or same size
4. in front or behind the mirror
Learn more about concave mirror images here.
The image properties depend on the
object’s location with respect to the
mirror, focus, and center of curvature.

14. object is beyond the center of curvature:
image is real, inverted, and reduced
object is on the center of curvature:
image is real, inverted, and the same size
object between center of curv. and focus:
image is real, inverted, and enlarged
object is on the focus:
no image; rays reflect parallel
object is inside the focus:
image is virtual, upright, and enlarged

15. Learn more about characteristics of convex mirror images here.
Images formed by convex (diverging) mirrors are always:
1. virtual
2. upright
3. reduced
4. located behind the mirror between the
vertex and focus

16. General Image Trends real images are always inverted
virtual images are always upright
real images are always in front
of the mirror
virtual images are always
behind the mirror
negative image distance means
virtual image
positive image distance means
real image