RAY MODEL OF
LIGHT
RAY MODEL
Light tends to travel in straight lines.
Light’s straight lines are represented by rays
which show the direction that light travels after it leaves
its source.
Each ray ends with an arrow to indicate the direction
of travel.
If more rays reach your eye the brighter
the object appears.
Opaque
Translucent
Transparent
Rays leaving the source and travelling toward an
object, travel parallel to one another.
The science of how light reflects and bends
is called Geometric Optics
RAY DIAGRAM RULES – PLANE MIRRORS
1. Plane Mirrors – any mirror that has a flat reflective surface
2. Ray diagrams MUST be drawn with a sharp pencil
3. Normal: dashed line drawn perpendicular to the mirror
at the point of reflection.
4. Incident ray: light coming towards the mirror.
5. Reflected ray: light coming out from the mirror.
incident
ray (i)
normal
reflected
ray (r)
RAY DIAGRAM RULES – PLANE MIRRORS
6. Angle of Incidence ( i ) :
the angle between the incidence ray and the normal.
7. Angle of Reflection: ( r ) :
the angle between the reflected ray and the normal.
incident
ray (i)
reflected
ray (r)
8. Angle of incidence and angle of reflection are measured from
the normal NOT from the mirror surface.
9. To find the image, extend the reflected rays
behind the mirror using dashed lines
PLANE MIRROR IMAGES
 Images are formed in the location where the
reflected light rays cross.
 Therefore, when your eyes detect reflected light
from a plane mirror your brain projects these light
rays backwards in a straight line.
Your brain thinks that there is a light source behind the
mirror and that this is where the light rays originate.
But the mirror is opaque so there is NOT a light source
behind the mirror.
This type of image is called a virtual image
A virtual image is an image formed by light coming from
an apparent light source behind the mirror.
The reflected light rays from a plane mirror will never cross in
front of the mirror.
However if the reflected light rays are extended behind the
mirror, the rays will appear to cross
and the image is found here.
WHERE THE IMAGE IS FORMED
http://www.youtube.com/watch?v=nrOg85VPQgw
CHARACTERISTICS OF IMAGES (L.A.S.T/L.O.S.T.)
Use the acronym LAST or LOST to describe the
characteristics of all images found during the geometric
optics unit.
Location of Image
•point where reflected rays actually cross or appear to cross
object
image
Attitude of Image
•image orientation compared to object: upright or inverted
upright
inverted
Size of Image
•comparison to the object – smaller, same, larger
smaller
same
larger
Type of Image
Real - reflected rays cross in front [solid lines]
Virtual - reflected rays appear to cross behind [dashed lines]
real
virtual
Why do you see the light shining through the window?
How is this effect created by light?