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Office: Gamow Tower, F-521 Email: ivan.smalyukh@colorado.edu Phone: 303-492-7277 Lectures: Tuesdays & Thursdays, 3:30 PM - 4:45 PM Office hours: Mondays & Wednesdays, 3 PM - 4 PM Grading Assistants: Jian Yao, Yiheng Lin, Hao Song.

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physics 1230 light and color ivan i smalyukh instructor

Office: Gamow Tower, F-521

  • Email:
  • ivan.smalyukh@colorado.edu
  • Phone: 303-492-7277
  • Lectures:
  • Tuesdays & Thursdays, 3:30 PM - 4:45 PM
  • Office hours:
  • Mondays & Wednesdays, 3 PM - 4 PM
  • Grading Assistants:
  • Jian Yao,
  • Yiheng Lin,
  • Hao Song

Physics 1230: LightandColorIvan I. Smalyukh, Instructor

  • Lectures
  • Homeworks
  • Exams
  • Hands-on experience
  • Demonstrations
  • Peer Instruction (with extra credit)
  • Fun
course business
Website

http://www.colorado.edu/physics/phys1230/phys1230_fa09/

Syllabus

Science of light and color

HW assignments, reading and exam dates

Course info

Grades

Clicker technology

Another kind of invisible wave

Course Business
physics 1230 light and color ivan i smalyukh
What is "science"?

Why is learning science like learning a foreign language?

Words have new and precise meanings

Wave, image, ray, lens, white, exposure, file, see, reflection, refraction, dispersion, particle

What does it mean for the "sun to set?" Is there really global warming? How could complex and magnificent creatures like us have evolved from lower species?

We all have scientific curiosity:

Why the sky is blue?

What is rainbow?

What is sunset?

How my laptop display works?

Physics 1230: LightandColorIvan I. Smalyukh
slide6

Ornithoptera chimaera chimaera

Ornithoptera goliath supremus, f. titan

Papilio blumei blumei

Ornithoptera priamus urvillianus

survey to be answered by clickers
What is your background for light and color? Choose the one which best describes your science background

I have had no physics in high school or college

I have had physics in high school but not in college

I have taken a physics course OR a psychology course at the college level

I have taken more than one physics or psychology courses (high school and/or college level)

I am a science major

Survey to be answered by clickers
survey to be answered by clickers12
Why did you take this course? Give the answer which best describes your reason.

Because of requirements by the university

Because it was recommended to me

Because it looked easy

Because it looked interesting

I don't know why

Survey to be answered by clickers
scientific notation and metric system
Powers of 10 give a shorthand notation for very large numbers.

103 = 1000

102 = 100

101 = 10

100 = 1

Or very small numbers

10-1 = 0.1

10-2 = 0.01

10-3 = 0.001

Scientists don't use feet or miles to indicate distances

They use

meters (m)

1 meter = 39.4 inches

kilometers (km)

1 km = 1000 m = 0.625 mi

centimeters (cm)

1 cm = 10-2 m = 0.394 inches

millimeters (mm)

1 mm = 10-3 m

nanometers (nm)

1 nm = 10-9 m

Scientific notation and metric system
clicker question
What Lottery Prize you prefer?

$ 103

$ 10-8

$ 107

$ 100

$ 10-18

wavelength = 500 nm = 5 x 102 x10-9 m = 5 x 10-7 m

Hence 1 m = wavelength/(5 x 10-7) = 107/5 wavelengths =2 million wavelengths

Since 1 cm is 1/100 of a meter there are 2 x 106/100 = 20,000 wavelengths in a cm

Clicker question
clicker question15
The wavelength of green light is around 500 nm. How many wavelengths of green light fit into one cm (or a fingertip)?

20 thousand

50 thousand

Two million

Two billion

5 billion

500 nm = 5 x 102 x10-9 m = 5 x 10-7 m

1 cm = 10-2 m;

Hence, 10-2 /(5 x 10-7) = 20,000 wavelengths in a cm

Clicker question
intro and chapter 1 continued
Light belongs to a family of waves called electromagnetic (EM) waves (Physics 2000)

Other waves: rope waves, water waves, sound waves, etc.

Sometimes EM waves are called EM radiation

Radio waves

Radar and similar waves

microwaves

cell phone waves

Infrared or heat waves

Ultra-violet (suntan) waves

X-rays

Gamma rays

EM waves are created and destroyed by emission and absorption

Classical picture (Phys 2000)

wiggling electrons radiate radio waves or radar waves

electrons in an atom are resonant with emitted or absorbed light waves or X-rays

Quantum picture (Phys 2000)

change of state of electrons in atoms when bundles of wave energy (photons) are emitted or absorbed

Light sources

Incandescent light bulb

Neon light

Fluorescent light

Intro and Chapter 1 Continued
rays a single beam of light for example
Single light ray

Ray from a laser acts like a single light ray

Illustrate by laser light through fog

Bounce off mirror

Bounce off white card

Put through water (bending)

We only see light when a ray enters into our eye

Laser light is visible from side because it is scattered into our eyes

Rays from a flashlight

Rays from a light bulb

What about light coming from everything in this room? Two kinds of objects:

Self luminous objects (lights)

Objects which are not self-luminous are seen because of light reflected off them

Turn out the light and we don't see anything in the room

It's all reflected light with many rays coming from diffuse surfaces

Rays(a single beam of light, for example)
slide21
Light rays are invisible unless they enter directly into our eye or are scattered bysmoke, fog or some object into your eye!

Seeing everything in terms of rays

Laser

MANY reflected rays comefrom all parts of Alex, includinghis nose - a diffuse object

Flashlight

Light

bulb

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
Rays bounce when they reflect off a mirror or shiny surface
  • This is called specular reflection.
  • How is it different from
  • diffuse reflection?

Mirror

rays bounce when they reflect off a mirror or shiny surface23
Rays bounce when they reflect off a mirror or shiny surface
  • This is called specular reflection.
  • How is it different from
  • diffuse reflection?

Mirror

slide24

http://phet.colorado.edu/sims/string-wave/string-wave_en.htmlhttp://phet.colorado.edu/sims/string-wave/string-wave_en.html

waves
Rope waves

Created by oscillation of my hand holding the rope

Finite speed of wave, but rope segments do NOT move in direction of wave

Rope segments move up and down, not along wave

Note the change that occurs when I oscillate my hand faster

Radio wave transmitter

3 meters wavelength

(100 Mhz frequency)

Google search under keyword "physics"

Water waves (circular pattern)

Stadium waves

Waves
period and frequency of a wave and relation to wavelength and speed
Period and frequency of a wave and relation to wavelength and speed

• The period, T, is the time for the wave to make one complete cycle (say, top-bottom-top) AT ONE FIXED SPOT

• The frequency, f, of the wave is equal to one over the period: f = 1/T

f has the units of 1/secs, which we call Hertz (Hz)

• The frequency, f, is related to the speed of the wave, c and its wavelength,  (lambda):

Think of my hand moving to make the rope wave. The period is the time for my hand holding the rope to make one complete top-bottom-top (or bottom-top-bottom) motion.

f  = c

we see color when waves of different wavelengths enter enter our eyes
We see color when waves of different wavelengths enter enter our eyes!

Light with wavelength of 650 nmappears red when it enters a viewers eye

Light with wavelength of 520 nmappears green when it enters a viewers eye

Light with wavelength of 470 nmappears blue when it enters a viewers eye

The speed of light in empty space is the same for all wavelengths

clicker questions
Which of the light waves has the longest wavelength?

Which of the light waves is brightest?

Which of the light waves has the highest speed in empty space?

b) c)

They all have the same speed

Clicker questions

a)

b)

c)

what happens when two or more waves with different wavelengths reach your eye
What happens when two or more waves with different wavelengths reach your eye?

Light with both wavelengths 650 nm and520 nm appears yellow when it enters a viewers eye

Light with only wavelength 580 nm

ALSO appears yellow when it enters a viewers eye (A DEEPER YELLOWTHAN FOR THE CASE ABOVE)

what is white light
What is white light?

Light which is a mixture of 650, 520 and 470 nm wavelengths (and possibly more wavelengths) appears WHITE when it reaches your eye

No single wavelength (mono-

chromatic) waveappears white

when it reaches your eye!

light at wavelengths which we see as colors are part of a wider family of electro magnetic waves
Light at wavelengths which we seeas colors are part of awider familyof electro-magneticwaves
it s a good idea to remember some rough wavelengths associated with colors
It's a good idea to remember some rough wavelengths associated with colors
  • Violet and blue are what we see when shorter wavelength visible rays enter our eyes.
    • They have relatively higher frequencies
  • Red is how we see longer wavelength visible rays
    • Red has a relatively smaller frequency
what happens when those other electromagnetic waves enter our eyes
What happens when those other electromagnetic waves enter our eyes?
  • We don't see anything becauseelectromagnetic waves at this frequency cannot excite aresonance in the atoms in our eyes.
    • Note that this wavelength is onthe order of a centimeter
    • These are microwaves just likethose sent out and received by yourcellphones (or used in a microwaveoven).
    • We cannot see them evenwhen they enter our eyes becausetheir wavelength is too long toexcite a resonance.

Wavelength = 10 million nm

  • Note that the frequency is
  • f = c/l
  • (3 x 108 m/s)/(10-2 m)

= 3 x 1010 Hz

how much time it takes for the wave to travel distance of 9000 km
How much time it takes for the wave to travel distance of 9000 km?
  • Speed of sound 340 m/s
  • Speed of electromagnetic waves 300,000 km/s ;
how does an ordinary incandescent light bulb work
How does an ordinary incandescent light bulb work?

Filament with current of electrons which hitinto atoms causing light to be emitted

Gas

Atom

Atom

Atom

Electrons

Light emitted at many different resonance frequencies of atoms appears as white light

Electrode leading to the other side ofthe wall plug

Electrode leading to oneside of the wall plug

slide61
Neon lights have atoms with resonances at special colors inside. They use alternating (AC) household current (Demo)

Atom

Atom

Atom

Electrons

Neon light

slide62
In this case the wavefront is expanding out spherically from the light bulb.

Wherever it intersects a ray the wavefront is perpendicular to that ray

More technically, the tangent to the wavefront at the point of intersection is perpendicular to the ray

The wavefront may be easier to visualize than the rays

You throw a pebble into a pond. The circularly expanding water waves are the wavefronts

Light

bulb

When rays come out in various different directions from an object or objects, the wavefront is defined as a curve or surface perpendicular to all the rays

Wavefront

Rays

how are wave wiggles related to rays

ray

Wiggles

Ray

Waveform

How are wave wiggles related to rays?

Light with a SINGLE

wavelength is called

monochromatic light

They are perpendicular

Amplitude {

Wavelength {

Speed of light in empty space is c = 186,000 miles/sec = 3 x 108 meters/sec

Note, the wave is NOT "red." I have colored it red.

We perceive it as red because of its wavelength.