2-Light
Open to 3. 1
Targets
I can explain the complex theory of what light is.
I can explain how light travels and converts into other forms of energy.
I can calculate the speed of light.
Sound and Light ComparisonLight Sound
Travels in…
Wave form
Wave vibrates
Medium
Type of Energy
Waves
Longitudinal
Parallel to direction of
travel
Some kind of matter
Mechanical
Sound and Light Comparison
Light Sound
Speed in….
Vacuum
Air
Water
Glass
Example
Energy
Much slower
0.0 m/s 340 m/s
1500 m/s
3000 m/s
Thunder
Changes with amplitude
What are the Sources of Light?
Sources: Primary: Sun Secondary: Brightness of Sky
Other Common Sources: Flames Filaments Glowing Gases
Properties of Light
Spreads out in all directions from its source
Travels as a wave in a straight line
Can travel in empty space as well as through
matter
See things because light reflects into our
eyes
Travels at the speed of light (c)
HISTORY of LIGHT
Early Concepts of Light
You do not need to write all of this down Greeks thought…. Light was tiny particles that entered the eye to
create the sensation of vision Vision was from your eyes emitting streamers
or filaments to an object
Early Concepts of Light
Empedocles 1st Greek to think light travels in waves
Particle Theory
Sir Isaac Newton Stated simple explanations Used the Laws of Reflection and Refraction to prove
that light travels as particles
Wave Theory
Christian Huygens (1678) Stated light travels as waves (same time as
Newton’s theory was widely accepted) Huygens argued diffraction
Wave Theory
Thomas Young (1801 experiment) 1st clear demonstration as wave Interference Behavior – just like lab
http://www.youtube.com/watch?v=T-hypvhhLeA
Dual Nature of Light
Einstein – 1905 Most influential papers ever written in Physics
In some cases light acts as a wave and in others it acts as a particle
Photons – small packet of
electromagnetic energy
traveling as a wave
LIGHT HISTORY RELATED TO ATOMIC STRUCTURE
http://www.youtube.com/watch?v=i1TVZIBj7UA
Drawing quantum mechanics by Plank
http://www.youtube.com/watch?v=BH0NfVUTWG4
What is Light?
Light is Energy!
Able to see because light reflects from sources to your eyes
Electromagnetic Spectrum
- spectrum of different light waves- light waves travel at the speed of light (c)
X-RaysMicrowaveUltraviolet
Visible Light
Infrared
GammaRaysRadio
Waves
Electromagnetic Spectrum(Please label your diagram in your notes)
Speed of Light
How does light travel?
Instantaneously?
Or
Finite Speed?
Measuring the Speed of Light
Galileo – light and mirrors- too quick to begin to measure
Olaus Roemer- 1st successful estimation (1675)
Christain Huygens- used Roemer’s Data and explained findings
Albert Michelson- 1st American to Receive Nobel Prize in 1907
Let’s Determine c with a μ-wave
v = f * λ
f = 2450 MHz = 2.450 x 109 Hz
λ = 12.2 cm = .122 m
v = 3.0 x 108 m/s
Mickelson’s Experiment 1880 Experiment
Proved Speed of light to be 3.0 x 108 m / s http://www.youtube.com/watch?v=lR4tJr7sMPM (1 min)
Light YearHow long is a light year?
Measurement of Distance!!!
The amount of distance light can travel in one year
Light from the Sun is from 8 minutes ago
Alpha Centauri- 4 year old lightNext closest star
Milky Way Galaxy – diameter – 100,000 ly
HOW BIG IS THE UNIVERSE REALLY?????
http://www.youtube.com/watch?v=XBr4GkRnY04 (5 min)
300,000,000 m/s or 186,000 mi/s
At this speed light can go around the world 7.5 times in one second
Doppler Effect for Light
Red Shift - decrease in frequency from an receding light sourcehttp://www.youtube.com/watch?v=FhfnqboacV0
Blue Shift - increase in frequency from an approaching source
http://www.youtube.com/watch?v=y5tKC3nEx2I
Sound and Light ComparisonLight Sound
Travels in… Waves
Wave form Longitudinal
Wave vibrates Parallel to direction of
travelMedium Some kind of
matterType of Energy Mechanical
Waves
Transverse
Right angles to direction of
travel
Not required
Electromagnetic
Sound and Light Comparison
Light Sound
Speed in…. Much slower
Vacuum 0.0 m/s
Air 340 m/s
Water 1500 m/s
Glass 3000 m/s
Example Thunder
Energy Changes with amplitude
Fastest known
1 c
.997 c
.750 c
.645 c
Lightning
Changes with frequency
Interference
• Same characteristics as in Ripple Tank Lab
• Addition or subtraction of waves
http://www.youtube.com/watch?v=BH0NfVUTWG4
Young’s Experiment
• Used “monochromatic” light with pin holes!
• Double Slit Experiment
• Verified Huygens proposal that light is a wave!
http://www.youtube.com/watch?v=6xKUass7G8w
Diffraction
• Bending of a wave by means other than reflection or refraction
• Occurs with all shadows
http://www.youtube.com/watch?v=-mIO9jqJyyI
Narrow Slit
• Diffraction causes a fuzzier shadow when the opening is extremely narrow
Wide Slit
• Casts a sharp shadow with some fuzziness at the edges
Diffraction Grating – An Interference Pattern
• Splits light into many beams of light traveling in different directions
• Direction varies with spacing and λ• Grating acts as a dispersive element
Iridescence
• Interference of light waves of mixed frequencies reflected from the top and bottom of thin films producing a spectrum of colors
• Common examples: soap bubbles, gasoline on a wet street
• Colors and complimentary colors
L.A.S.E.R.S
Light Amplification by Stimulated Emission of Radiation
Albert Einstein in 1917 first theorized “Stimulated Emission” within Special Relativity
Brief History
Idea of a LASER was first contrived by Charles Townes and Arthur Schawlow in 1958
1960: Theodore Maiman invented the ruby LASER considered to be the first successful optical or light laser.
How does a LASER work? Regular light emitted from a
common lamp is incoherent
What does incoherent mean? LASER light is coherent!
What does coherent mean?
Every beam of light has the same frequency, phase, and direction (=same color of light)
No wave interference within the beam
How a LASER Works!
The excitation of electrons
Light is given off when electrons drop energy levels
http://www.youtube.com/watch?v=oUEbMjtWc-A
Different Types of Lasers Solid-state LASER
Gas LASER
Excimer LASER
Dye LASER
Solid-State LASER
Have lasing material distributed in a solid matrix= Ruby laser
Gas LASER
Have a gas lasing material= helium and helium-neon LASER
Excimer LASER
Doctor Steven Trokel patented for vision correction
Performed first LASIK in 1987
When lased, the dimmer produces light in the ultraviolet range
Dye LASER
Use complex organic dyes in liquid solution
Tunable over a broad range of λ
How can a LASER be used for communication? DEMO!!!
Holograms
Produces a 3-D version of a photograph
Relies upon an interference of light
Basic Setup for How Holograms Work
How to make a holographic image!
1. Aim LASER at the beam splitter (creates 2 rays)
2. Align the mirrors3. Diverging Lenses-
widen beam4. Object beam reflects
off object to the film5. Reference beam
travels to the holographic film
Holographic Image
The 3-D image produced by a hologram
Holographic Image Magazines and Books
What happens if you tear a holographic image?
Hologram Presentation
How its Made: Holograms5 minutes
JFL:
http://www.youtube.com/watch?v=fkNcqNQLuRQ
Mirrorshttp://www.youtube.com/watch?v=nTXoR
Hi9uKY
Member #2…
Retrieve a small white board, an eraser and a marker.
Do this question:
1. How far, in meters, can a beam of uninterrupted light travel in one year? (This distance is known as
one light year.)
1. How far, in meters, can a beam of uninterrupted light travel in one year? (This distance is known as one light year.)
m158
9.5x10 s 1
m 3x10x
hour 1
s 3600x
day 1
hours 24x
year 1
days 365x
year 1
31500000
d103 8 x
t
dv
m9.5x10d 15
Do question 2:
2. Pluto is 5.91x1012 m from Earth. How long does it take light to travel from Pluto to Earth?
d = 5.91x1012 m
v = 3x108 m/s
t = ?
2. Pluto is 5.91x1012 m from Earth. How long does it take light to
travel from Pluto to Earth?
t
dv
t
m 5.91x10m/s 103
128 x
sec 19700t
Do question #3
3. Different colors of light have different wavelengths and frequencies but they all travel at the speed of light. What is the frequency of yellow light (λ=556 nm)?
f = ?
λ = 556 nm
v = 3x108 m/s
3. Different colors of light have different wavelengths and frequencies but they all travel at the speed of light. What is the
frequency of yellow light (λ=556 nm)?
m 5.56x10 nm 1x10
m 1x
nm 556 7-9
fv m 5.56x10 m/s 3x10 -78 f
Hz 104.5 14xf
Do question 4
4. The distance to the moon can be found with the help of mirrors left on the moon by astronauts. A pulse of light sent to the moon will return in 2.562 s. Calculate the distance from Earth to the moon.
d = ?
v = 3x108 m/s
t = 2.562 s
*Must divide
time by 2
4. The distance to the moon can be found with the help of mirrors left on the moon by astronauts. A pulse of light sent to the moon will return in 2.562 s. Calculate the distance from Earth to the moon.
s 1.281
dm/s 103 8 x
t
dv
m 10843.d 8x
5 fun phenomena
http://www.youtube.com/watch?v=1Xp_imnO6WE
Explanations:http://www.youtube.com/watch?v=jIMihpD
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