Download Class 9

Physics 1230: Light and Color
Ivan I. Smalyukh, Instructor
Office: Gamow Tower, F-521
Email:
[email protected]
Phone: 303-492-7277
Lectures:
Tuesdays & Thursdays,
3:30 PM - 4:45 PM
Office hours:
Mondays & Fridays,
3:30 PM – 4:30 PM
TA: Jhih-An Yang
[email protected]
Class # 9
HW #1 (out of 10 points maximum)
Exam #1:
September 29 or October 4?
Clicker question: which of the
following statements is true
• A. We can see two rainbows after the rain;
• B. The observation of primary rainbow involves total
internal reflection, refraction at 2 droplet-air interfaces,
and dispersion;
• C. The observation of the secondary rainbow involves
two total internal reflections, refraction at 2 droplet-air
interfaces, and dispersion;
• D. All of the above;
• E. None of the above.
4
How we see two rainbows
two total
internal
reflections
sun
total internal
reflection
5
6
Total internal reflection makes
fiber optic communication possible
The ray bends from the low n
material toward the high n material.
Demo: glass tube, laser pointer
7
Time for a demo!
If we pull the cork, and water starts to pour
out of the tank, the laser light will…
A) Shine across the room to the wall.
B) Stay entirely inside the tank
C) Stay entirely inside the water stream
D) Something else happens.
8
This illustration appears
in "La Nature" magazine
in 1884.
Demo: tank
9
Lec. 6: Ch. 2 - Geometrical Optics
1.
2.
3.
4.
We
are
here
Shadows
Reflection
Refraction
Dispersion
Move to Chap. 3
1. Virtual images
10
10
How does the eye make sense of all these light rays?
A)
B)
C)
D)
Uniform background
Several points of light
This is not an image
No idea.
You are not aware
of all those rays,
but rather of 3
11
points of light
Chapter. 3 – Spherical Mirrors and Lenses
We
are
here
1.
2.
3.
4.
Virtual images (review)
Spherical mirrors
Spherical lenses
Aberrations of lenses
http://en.wikipedia.org/wiki/Lens_%28optics%29
Skip 3.3c anamorphic art.
12
Review: plane mirrors, specular reflection
• Equal angle rule
• Similar triangles are useful
qi
qr
Normal
Mirror
• Ray tracing a mirror
Xobject = Ximage
Image point is on the normal
(mirror might need an
extension)
Xobject
Extension
Ximage
13
Review: What is an object? What is an
image?
Xobject
Extension
Ximage
=
We will often replace a real object (say a bottle)
with an arrow, to simplify the drawing.
14
Review: What is an object?
What is an image?
Xobject
Extension
Ximage
=
In this context, an object is a point, or set of many points,
that emits light rays in a range of directions:
15
What is an image? X
object
Extension
Ximage
=
16
Curved Mirrors
First, a little geometry review:
This line segment (from center of circle)...
...is perpendicular
(or normal) to this
tangent.
17
Rays reflecting from a convex
(spherical) mirror
• Ray aimed toward center
of sphere comes straight
back (specular reflection
with normal incidence)
• What about other rays?
All rays aimed at the center C
come straight back out.
C
18
What happens to all rays that come in
parallel to the OPTICAL AXIS (the line
running through C)?
• Specular reflection
• Find where incoming ray
hits mirror surface
• Find surface normal at
that point (along line from
center--remember
geometry review?)
• Angle of incidence = angle
of reflection
• Reflection (of parallel
ray) looks like it’s
coming from F -- turns
out this is true for all
parallel rays!
F
C
qi
qr
The focus is halfway to
the center
19
What happens to all rays that
come in parallel?
Focal point = focus
is behind the surface
• Easy rule for parallel
incoming rays (parallel to
the line through F and C):
they are reflected as if
they came from F.
F
C
The focus is halfway to
the center
20
What about rays aimed at the focus?
(This is the previous rule, backwards)
• Easy rule for rays aimed
at focus:
• An incoming ray aimed
at F gets reflected back
parallel (to the C-F axis).
Focal point = focus is
behind the surface
F
C
The focus is halfway to
the center
21
Three easy rules for convex,
spherical mirrors
1. All rays incident parallel to the CF axis are reflected so that they
appear to be coming from the
focal point F
2. All rays that (when extended)
pass through the center C are
reflected back on themselves.
3. All rays that (when extended)
pass through the focal point F
are reflected back parallel to the
axis
3
F
1
C
2
22
Ray tracing: convex mirror
F
C
What does the observer see
in the mirror?
23
Ray tracing: convex mirror
F
C
What does the observer see
in the mirror?
Draw in the rays and extrapolate back
24
Ray tracing: convex mirror
F
(A) Or (B) ??
• Is the image real or virtual?
• Is the image larger or smaller than the object?
• Is the image right-side-up or upside-down?
• How could a mirror be useful when used like this?
C
25
Rays reflecting from concave
(cavity) mirrors
Ray through the center
reflects straight back at
its source
C
26
Incoming parallel rays reflect
through focus
• All (incoming parallel) rays
reflect and go through the focus
half way from center to mirror
C
F
As usual, this rule works backwards: incoming rays that go
through the focus reflect back parallel (to the C-F axis).
27
Rays through focus reflect back
parallel to C-F axis.
C
F
28
Concave mirrors are very useful
C
light beam emitter
(flashlight)
F
solar light collector
or oven
29
Three easy rules for concave,
spherical mirrors
1. All rays incident parallel to the
C-F axis are reflected through
the focal point F
2. All rays that pass through the
center C are reflected back on
themselves.
3. All rays that pass through the
focal point F are reflected back
parallel to the axis
1
C
F
2
3
30
Ray tracing: concave mirror object outside center
C
F
31
Ray tracing: concave mirror object outside center
C
Questions: (A) OR (B)
• Is the image real or virtual?
• Is the image larger or smaller than the object?
• Is the image right-side-up or upside-down?
• How could a mirror be useful when used like this?
F
32
Ray tracing: concave mirror object between
center and focus
C
Questions:
• Is the image real or virtual?
• Is the image larger or smaller than the object?
• Is the image right-side-up or upside-down?
• How could a mirror be useful when used like
this?
F
33