1. Light , Mirrors, and Lenses

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

3. Angles are ALWAYS measured from the NORMAL LINE
Law of Reflection
(Angle of Incidence = Angle Reflection)
Normal
Line
Incident
ray
Reflected
ray i r
Mirror surface
Angles are ALWAYS measured from the NORMAL LINE

4. Reflection from a mirror:
Normal
Incident ray
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
Reflections from a Plane Mirror
Dotted lines
Shows the
Apparent
Ray source
Angle of incidence = Angle of Reflection
For each ray

7. Concave Mirrors (Converging Mirrors) Real Focus Parallel rays
Focal length = +
Forms real, inverted,
Reduced or enlarged
Image. Also forms
Virtual, erect,
Enlarged images.
Reflected rays

8. Convex Mirrors (Diverging Mirrors) Virtual focus Parallel rays
Focal length = -
Forms only virtual,
erect, reduced
images between
the virtual focus
and the mirror.
Reflected rays

9. Image in a Convex Mirror
Apparent
Convergence of rays
Parallel ray
Ray thru 2f
Focal ray
(f)
2 f
Image is:
Virtual
Erect
Reduced
Appears behind the
mirror

10. Image in a Convex Mirror
Virtual focus
Dotted lines
Shows the
Apparent
Ray focus
Parallel rays
Focal length = -
Forms only virtual,
erect, reduced
images between
the virtual focus
and the mirror.
Reflected rays

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. Refraction of Light i = angle of incidence r = angle of refraction
Normal
Line
i = angle of incidence
r = angle of refraction i
Air
n =1.0 i
Glass
n = 1.5 r
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 r
Normal
Line

13. Diverging Lens (Double Concave) Virtual focus Focus = -
Can form only virtual,
Erect and reduced
images

14. Enlarged virtual images
Converging Lens
(Double Convex)
Principle
focus
Parallel rays
Focus = +
Can form real images
(enlarged or reduced
& inverted) or
Enlarged virtual images

15. Colored light is made from white light by REFRACTION,
but we see color because of REFLECTION.
Which color refracts most leaving the prism? The least?

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 red and green makes yellow
Adding all three makes white again

18. Only red light is reflected
Seeing color
The color an object appears depends on the colors of light it reflects.
For example, a red book only reflects red light:
Homework
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
A white hat would reflect all seven colors:
White
light