Transcript Class 2 - University of Colorado Boulder

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 # 2
Using iClickers
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•
•
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Everyday: swap clicker code to DC
Wait for 1st clicker question to open
Hold down On/Off Switch 4 seconds
Flashing blue light: hit D C
Type in Answer.
you’re set for rest of class period
• DO NOT TURN OFF CLICKER FOR CLASS
(o.w. repeat above for any new clicker question)
2
A Light-ning Blitz through the
course material
Let’s see some of the major
things we’ll cover in the class.
3
Light rays and what we “SEE”
Straight-line paths and what enters the eye.
4
Electromagnetic spectrum
c=fl
Wavelength
Frequency
Speed of light
5
Electromagnetic waves can have any wavelength
Scientific notation is useful!
6
Shadows, reflection,
refraction
– Ch. 2
7
Lenses and mirrors – Ch. 3
8
Lenses and mirrors – Ch. 3
Precise mathematics let’s you DESIGN lens systems.
9
Photography – Ch. 4
Image recording digital
10
The Eye – Ch. 5
Visual systems in
other creatures.
11
Optical instruments – Ch. 6
Telescopes
12
The “Very Large Array”
‘near’ Socorro, NM.
13
Optical instruments – Ch. 6
Microscopes
Robert Hooke’s
circa 1660
Modern laser confocal
14
Your eyes can play tricks on you – Ch. 7
15
Visual Processing – Ch. 7
16
Visual Processing – Ch. 7
17
Color – Ch. 9
18
Color perception – Ch. 10
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Color perception – Ch. 10
The sum of the two number is:
A) 18
B) 20
C) 23
D) 25
20
Scattering & Polarization – Ch. 13
21
Holography and Lasers – Ch. 14 & 15
22
Break for
th
7
inning stretch.
Something to ponder during the stretch:
WHY (and how) do we see things?
Favorite answers:
Because…
Because there is LIGHT…
We want to
understand these
things
Because we have EYES…
Because creatures that see tend to survive…
23
First goals of the course:
Understand enough about light to be
able to talk about it. Develop our first
model for how light behaves and how
we SEE things.
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Disappearing glass rods…
http://www.youtube.com/watch?v=pNWCB_GoQA
4
http://www.youtube.com/watch?v=7hOZJL_bEPQ
25
Cloaks of invisibility?
http://www.youtube.com/watch?v=mcPzCb7TlZ8&NR=1
26
What do you already know
about light?
Please, make a list with :
•Spectrum
•Wave and particle properties
•Source of energy momentum
•Fast speed
•Straight line unless it interacts
27
Light rays are invisible unless they enter
directly into our eye or are scattered by
smoke, fog or some object into your eye!
Laser
Flashlight
Light
bulb
MANY reflected rays come
from all parts of Alex, including
his nose - a diffuse object
Incident ray from a light bulb
Bob sees Alex's nose because a reflected light ray enters Bob's eye!
Rays bounce when they reflect off a
mirror or shiny surface
• This is called specular reflection.
• How is it different from
diffuse reflection?
Mirror
To understand light better we
need to know about Waves
• Electric fields
• Magnetic fields
• Light is an ‘electromagnetic wave’
E
B
30
QUALITATIVE things about
electric forces
A)
B)
C)
D)
There are two types of charge
There is only one type of charge
There are more than two types
None of the above.
A)
B)
C)
D)
Like charges attract
Like charges repel
Opposite types repel
Depends on the situation.
And opposites
attract
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QUANTITATIVE statement:
Coulomb’s Force Law:
Q
Depends on the
charges
qQ
FqQ  k 2
r
r
distance
q
Constant of
nature.
What is the force that q
feels from Q?
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A question:
You are given three numbers, a, b, and c.
True or false: The combination of
numbers
ab
c
is always equal to:
A) TRUE
B) FALSE
b
a
c
Experiment: Try some actual
numbers, like a=2, b=3, c=4
and test it.
33
You are given four numbers, a, b, c, and d. Which
of these are valid ways to rewrite ab
b
A) a cd
1
a
B) b
cd
 1   ab 
C)    
 c  d 
cd
Experiment can be valuable
here too…
D) All of the above
E) None of the above
34
QUANTITATIVE statement:
Coulomb’s Force Law:
Q
Depends on the
charges
qQ
FqQ  k 2
r
r
distance
q
Constant of
nature.
What is the force that q
feels from Q?
35
Useful to rewrite things:
Coulomb’s Force Law:
qQ
FqQ  k 2
r
Which is another way to write this force law?
A)
B)
C)
qQ
FqQ  k 2
r
q Q
FqQ  2 k 2
r r
 Q
FqQ  q  k 2 
 r 
D)
None of these
E)
All of these
36
The universe divides into two parts:
Coulomb’s Force Law:
FqQ
 Q
 qk 2 
 r 
Property of the
local THING,
say YOU.
We Say:
Fq  r   qE
Properties of
the rest of the
universe.
ELECTRIC FIELD
due to the rest of the
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universe.
Suppose we have 3 charges:
The force felt by q …
Q1
r1
A) Can still be F=qE
B) Cannot be F=qE
Q2 C) MAY be F=qE if the
charges are in a line.
r2 D) Something else
happens.
q
qQ1 qQ2
Q2 
 Q1
FqQ  k 2  k
 q  k 2  k 2   qE
2
r1
r2
r2 
 r1
38
Electric Fields
We Say that charges
feel a force:
ELECTRIC FIELD
due to the rest of the
universe.
Fq  r   qE
The charge
value.
Properties of
the rest of the
universe.
39
What do you already know
about magnetism?
A) Magnets come with only a north pole
B) Magnets come with only a south pole
C) Magnets come with both a north and
south pole.
D) Depends upon the type of magnet.
A)
B)
C)
D)
GUESS WHAT:
Like poles attract
The universe
Like poles repel
produces
Opposite poles repel
Magnetic
Fields
Depends on the situation.
too.
40