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Light 1.pptx
1. Properties of Light summary
1) Light doesn’t need medium to propagate
(electromagnetic wave)
2) Light propagates as a transverse wave
3) Light travels in straight lines
4) Light travels much faster than sound
5) We see things because they reflect light
into our eyes
6) Shadows are formed when light is blocked
by an object
2. Reflection
Reflection from a mirror:
Incident ray
Normal line
Reflected ray
Angle of
incidence
Angle of
reflection
Mirror
3. The Law of Reflection
Angle of incidence = Angle of reflection
In other words,
light gets reflected from a surface at ___ ______angle it hits it.
the same!
4. 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. Examples of light reflection
60°
70°
2nd reflector
Incident ray
Determine the angle of reflection on 2nd reflector!
7. The Formation of Images by a Plane Mirror
Your image in a flat mirror has four properties:
1. It is upright.
2. It is the same size as you are.
3. The image is as far behind the mirror as you
are in front of it.
4. It is reversed, left <--> right
The person’s right hand becomes
the image’slefthand.
Emergency vehicles are usually
reverse-lettered so the lettering appears
normal in the rear view mirror of a car.
8. The Formation of Images by a Plane Mirror
A ray of light from the top of the chess piece reflects from the
mirror. To the eye, the ray seems to come from behind the
mirror.
Because none of the rays actually emanate from the image, it is
called a virtual image.
Each point of an illuminated object
emits a continuum of light rays in a
range of directions. Two of these
rays are shown here.
9. The Formation of Images by a Plane Mirror
The geometry used to show that the image distance di is equal
to the object distance do.
Since by intersecting
lines,
Thus ABC and BCD are similar
triangles.
Since the triangles share the
common side BC, they are also
identical triangles, so
do = di
12. The Formation of Images by a Plane Mirror
Conceptual Example 1 Full-Length Versus Half-Length Mirrors
What is the minimum mirror height necessary for her to see her full
image?
Start with a mirror which is exactly her height.
Based on this reflection, the
length of the plane mirror
required to see her full image is
only half of her body height.
13. The Formation of Images by a Plane Mirror
Conceptual Example 2 Multiple Reflections
A person is sitting in front of two mirrors that intersect at a right angle.
The person sees three images of herself. Why are there three, rather
than two, images?
𝒏 =
𝟑𝟔𝟎°
𝜽
− 𝟏
Where:
n = number of images formed
θ = angle between two mirrors
