Physics 1230: Light and ColorIvan I. Smalyukh, Instructor

Office: Gamow Tower, F-521Email:

ivan.smalyukh@colorado.edu

Phone: 303-492-7277

Lectures: Tuesdays & Thursdays,

3:30 PM - 4:45 PMOffice hours:

Mondays & Fridays, 3:30 PM – 4:30 PM

TA: Jhih-An Yang jhihan.yang@colorado.edu 

Class # 2

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Using iClickers

• 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)

A Light-ning Blitz through the course material

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Let’s see some of the major things we’ll cover in the class.

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Light rays and what we “SEE”

Straight-line paths and what enters the eye.

5

Electromagnetic spectrum

c = f

Wavelength

Frequency

Speed of light

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Electromagnetic waves can have any wavelengthScientific notation is useful!

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Shadows, reflection, refraction – Ch. 2

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Lenses and mirrors – Ch. 3

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Lenses and mirrors – Ch. 3

Precise mathematics let’s you DESIGN lens systems.

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Photography – Ch. 4

Image recording - digital

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The Eye – Ch. 5

Visual systems in other creatures.

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Optical instruments – Ch. 6

Telescopes

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The “Very Large Array” ‘near’ Socorro, NM.

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Optical instruments – Ch. 6

Microscopes

Robert Hooke’s circa 1660

Modern laser confocal

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Your eyes can play tricks on you – Ch. 7

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Visual Processing – Ch. 7

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Visual Processing – Ch. 7

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Color – Ch. 9

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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

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Scattering & Polarization – Ch. 13

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Holography and Lasers – Ch. 14 & 15

Break for 7th inning stretch.

Something to ponder during the stretch:

WHY (and how) do we see things?

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Favorite answers:

Because…

Because there is LIGHT…

Because we have EYES…

Because creatures that see tend to survive…

We want to understand these things

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…

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http://www.youtube.com/watch?v=7hOZJL_bEPQ

http://www.youtube.com/watch?v=pNWCB_GoQA4

Cloaks of invisibility?

26http://www.youtube.com/watch?v=mcPzCb7TlZ8&NR=1

What do you already know about light?

•Spectrum

•Wave and particle properties

•Source of energy momentum

•Fast speed

•Straight line unless it interacts

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Please, make a list with :

Laser

Flashlight

Lightbulb

Incident ray from a light bulb

MANY reflected rays comefrom all parts of Alex, including

his nose - a diffuse object

Bob sees Alex's nose because a reflected light ray enters Bob's eye!

Light rays are invisible unless they enter directly into our eye or are scattered bysmoke, fog or some object into your eye!

Rays bounce when they reflect off a mirror or shiny surface

Mirror

• This is called specular reflection.

• How is it different from diffuse reflection?

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To understand light better we need to know about Waves

• Electric fields• Magnetic fields• Light is an ‘electromagnetic wave’

E

B

QUALITATIVE things about electric forces

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A) There are two types of chargeB) There is only one type of chargeC) There are more than two typesD) None of the above.

A) Like charges attractB) Like charges repelC) Opposite types repelD) Depends on the situation.

And opposites attract

QUANTITATIVE statement:

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Coulomb’s Force Law:

2qQF kqQr

q

Qr

Constant of nature.

Depends on the charges

distance

What is the force that q feels from Q?

A question:

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You are given three numbers, a, b, and c. True or false: The combination of numbers

abc

A) TRUE

B) FALSE

ba

cis always equal to:

Experiment: Try some actual numbers, like a=2, b=3, c=4 and test it.

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You are given four numbers, a, b, c, and d. Which of these are valid ways to rewrite ab

cdA)

B)

C)

D)

E)

ba

cd1

abcd

1d

abc

All of the above

None of the above

Experiment can be valuable here too…

QUANTITATIVE statement:

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Coulomb’s Force Law:

2qQF kqQr

q

Qr

Constant of nature.

Depends on the charges

distance

What is the force that q feels from Q?

Useful to rewrite things:

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Coulomb’s Force Law:2qQF k

qQr

Which is another way to write this force law?

A)

B)

C)

D)

E)

2qQF q kQr

2 2qQF kq Qr r

2qQF kq Q

r

None of these

All of these

The universe divides into two parts:

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Coulomb’s Force Law:

2qQF q kQr

Property of the local THING, say YOU.

Properties of the rest of the universe.

We Say: qF qEr ELECTRIC FIELD due to the rest of the universe.

Suppose we have 3 charges:

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The force felt by q …

2 2 2 2

1 2 1 21 2 1 2qQF k k q k k qE

qQ qQ Q Qr r r r

q

Q1r1

A) Can still be F=qEB) Cannot be F=qEC) MAY be F=qE if the

charges are in a line.D) Something else

happens.

Q2

r2

Electric Fields

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The charge value. Properties of

the rest of the universe.

We Say that charges feel a force:

qF qEr

ELECTRIC FIELD due to the rest of the universe.

What do you already know about magnetism?

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A) Magnets come with only a north poleB) Magnets come with only a south poleC) Magnets come with both a north and

south pole.D) Depends upon the type of magnet.

A) Like poles attractB) Like poles repelC) Opposite poles repelD) Depends on the situation.

GUESS WHAT: The universe produces Magnetic Fields too.