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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