2. Properties of Light
Light travels in straight lines.
Light travels ~ 300,000 km/s
Reflection – bouncing back (mirrors)
Refraction – bending due to different
mediums (lenses)
Laser
4. • Reflection from a mirror:
Incident ray
Normal
Reflected ray
Angle of incidence Angle of
reflection
Mirror
5. Clear vs. Diffuse Reflection
• Smooth, shiny surfaces
have a clear reflection:
Rough, dull surfaces have a diffuse
reflection.
Diffuse reflection is when light is
scattered in different directions
6. Angle of incidence = Angle of Reflection
For each ray
Dotted lines
Shows the
Apparent
Ray source
10. Parallel rays
Reflected rays
Virtual focus
Focal length = -
Forms only virtual,
erect, reduced
images between
the virtual focus
and the mirror.
Dotted lines
Shows the
Apparent
Ray focus
11. 2. Refraction
Refraction is when waves ____ __ or slow down due to travelling
in a different _________. A medium is something that waves will
travel through. When a ruler is placed in water it looks like this:
In this case the light rays are slowed down by the water and are
_____, causing the ruler to look odd. The two mediums in this
example are ______ and _______.
Words – speed up, water, air, bent
12. Normal
Line
Normal
Line
i
r
i
r
Glass
n = 1.5
Air
n =1.0
r = angle of refraction
i = angle of incidence
Light travels more slowly
in glass than air and
bends towards the normal
when entering glass from air
Light moving from
glass to air
increases speed
and bends away
from the normal
15. Which color refracts most leaving the prism? The least?
Colored light is made from white light by REFRACTION,
but we see color because of REFLECTION.
16. • We see things because they reflect
light into our eyes:
Homework
17. Adding colors
• White light can be split up to make separate colors. These
colors can be added together again.
• The primary colors of light are red, blue and green:
Adding blue and red
makes magenta
(purple)
Adding blue and green
makes cyan (light blue)
Adding all three
makes white
again
Adding red and
green makes
yellow
18. Seeing color
• The color an object appears depends on the colors of light
it reflects.
For example, a red book only reflects red light:
White
light
Only red light is
reflected
19. A white hat would reflect all seven colors:
A pair of purple trousers would reflect purple light (and red and
blue, as purple is made up of red and blue):
Purple light
White
light
