Properties of Light

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• Properties of Light

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Speed of E.M. Spectrum Waves in a Vacuum

• 299,792,458 m/s (3 x 108 m/s), or 186,000 miles
  per second.
• It takes about two and a half seconds, for
  instance, for a radio communication traveling at
  the speed of light to get to the moon and back.
• Speed decreases as density of medium increases
• Change in medium causes refraction (bending)
• At this speed it can go around the world 7.5
  times in one second

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Electromagnetic Waves

• Electromagnetic Waves - energy-carrying waves
  emitted by vibrating electrons
• Light, Radiation, or Photons

http//cse.ssl.berkeley.edu/img/em_wave.gif
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Electromagnetic Spectrum

Cosmic rays Background radiation particles of enormous energy given off by stars.
Gamma radiation Deadly high energy given out by the sun and other stars.
X rays High energy used in X ray equipment.
Ultraviolet rays Invisible energy waves in sunlight, which cause skin to tan.
Visible light Basic colors of light, emitted by the sun and visible to the human eye.  ROYGBIV.
Infrared rays Rays of heat energy sensed by our nervous system.
Radio waves Microwaves TV radio energy

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Radio Waves

• Longest wavelength, lowest frequency (smallest
  amount of energy)
• Used for radio, television, cellular phones,
  cordless phones, radio astronomy, microwaves, and
  RADAR
• Types
• Shortwave (for very long ranges)
• AM (can bend around large objects such as
  mountains)
• FM (strong signals in range of about 50-70 miles)
• Television broadcast waves (FM for sound and AM
  for picture)

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Infrared Radiation

• Heat
• Thermograms show how much infrared radiation is
  being given off by a living thing
• Used to view objects in the dark
• night vision goggles
• Heat lamps use infrared radiation to heat food

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Visible Light

• Only part of the EM spectrum humans can see
• 4 x 1014 Hz to 7.9 x 1014 Hz
• Visible spectrum of color (from longest
  wavelength to shortest)
• Red (650 nanometers)
• Orange
• Yellow (580 nanometers)
• Green (530 nanometers)
• Blue (470 nanometers)
• (Indigo)
• Violet (400 nanometers)

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Visible Light

• What we call light depends on the overall
  sensitivity of the eye, ranging in wavelength
  from 380 nm to 760 nm.

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Ultraviolet Radiation

• Causes us to make vitamin D in our skin
• Can be harmful
• can cause skin cancer
• Used to kill germs and sterilize medical
  equipment
• Nail shops
• Safety goggles

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X rays

• Their high energy makes then pass through many
  materials
• Various exposure times allows for numerous views

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Gamma Rays

• Most energetic
• Used in radiation therapy to kill cancer cells

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Important Properties of Light

• Amplitude determines brightness
• The greater the amplitude, the greater the
  brightness
• Wavelength determines color

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Light Intensity

• Intensity or brightness of the light changes
  along with the colors

http//fuse.pha.jhu.edu/wpb/spectroscopy/basics.h
tml
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Inverse Square Law
http//www.anees.com/6.html
http//www.astrosociety.org/education/publications
/tnl/32/starscience2.html
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Additive Primary Colors of Light

• By overlapping or adding various colors of
  light together almost any color can be made.

Additive PrimariesRGBRed, Green, and BlueLight
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Secondary Colors of Light

• Colors made by mixing 2 primary colors.
• G R yellow
• R B magenta
• B G cyan

http//www.colorado.edu/physics/2000/tv/colortv.ht
ml
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Light Mixing (Additive)

• White light is formed where red, blue and green
  light overlap

http//sol.sci.uop.edu/jfalward/reflection/reflec
tion55.html
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Photons

• Light and EM radiation are composed of small
  particles called photons.
• Photons are thought to be carriers of EM force.
• Have either particle or wavelike behavior. This
  duality in the nature of photons is a key aspect
  of Quantum theory.

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Different Wavelengths

• Medium dictates speed
• Since the photon's energy does not change, its
  frequency cannot change therefore its wavelength
  changes.
• Wavelength decreases as the speed decreases.

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Particle or Wave?

• Particles are discrete
• energy is concentrated into what appears to be
  finite space is homogeneous with definite
  boundaries
• Waves, not considered a finite entity.
• Light energy does not exist in a single location,
  as a wave varies in both place and time.

http//www.savagechickens.com/tag/particle
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Wave Theory VS Particle Theory Photon-massless
bundle of concentrated electromagnetic energy

• Particle Theory
• Light acts like particles that stream from the
  source (creating shadows)

• Wave Theory
• Light acts like wavesripples in space

http//www.thespectroscopynet.com/Educational/wave
_particle_duality.htm
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Dual Nature of Light
Proof that Light is a wave Proof of Nothing Proof that light is a Particle
Diffraction (particles dont change direction as they pass BY a barrier) Interference (two or more particles can NOT exist in the same place at the same time) Polarization (polarized filters allow light which is vibrating in one direction through only transverse waves can be polarized Reflection Refraction Photoelectric effect (When light hits a photoemissive metal, electrons are knocked off) Proves light is a particle since each photon knocks loose one electron Compton Effect (light can collide with small particles change their momentum)
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Duality of Light

• Wave-Particle Duality not strictly one or the
  other
• Quantum electrodynamics (QED) combines the
  wave-particle nature of light into a single
  theory.
• Light behaves as a wave
• When light travels through an opening
• Light behaves as particles
• when light bounces off of metal

http//nobelprize.org/nobel_prizes/physics/article
s/ekspong/index.html
http//www.crcs.k12.ny.us/physics/notes/modern/mod
ern_note.htm
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Photoelectric effect

• The photoelectric effect refers to the emission,
  or ejection, of electrons from the surface of,
  generally, a metal in response to incident light.

• Discovered by Einstein in the early 20th century
• electrons are ejected from a solid when impinged
  upon by electromagnetic radiation
• excitation
• led to the understanding of light as particles,
  or photons

http//www.physics.uiowa.edu/adventure/fall_2005/o
ct_15-05.html
http//www.uwsp.edu/geo/faculty/ritter/geog101/tex
tbook/energy/nature_of_electromagnetic_radiation_p
_2.htm
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Light as a Particle
http//www-inst.eecs.berkeley.edu/cs39j/sp02/sess
ion07.html
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Polarization

• The process of transforming non-polarized light
  into polarized light is known as polarization.
• Polarized light waves are light waves in which
  the vibrations occur in a single plane.

http//www.glenbrook.k12.il.us/gbssci/phys/Class/l
ight/u12l1e.html
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Light reflected from a horizontal surface is
partially polarized in the horizontal plane.
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http//www.olympusmicro.com/primer/lightandcolor/p
articleorwave.html
Polarized Light wave not particle

• Light consists of transverse waves having
  components that are perpendicular to the
  direction of propagation.

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Polarized Lenses Really Make a Difference!

• Light reflected from surfaces like a flat road or
  smooth water is generally horizontally polarized.
  
• Vertically oriented polarized lenses result in a
  reduction in glare.
• Eliminate reflected glare
• Enhance contrast
• Great for use during snow or water sports

http//www.chicagopearle.com/eyeglasses/lenses/pol
arized/index.asp
http//www.spyoptic.com/img/4219_tridentPolarized
.jpg
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Are your lenses polarized?
http//www.agape1.com/polarized.htm
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3-D Glasses

• Two projectors project two respective views onto
  the screen
• each with a different polarization.
• The glasses are polarized oppositely
• allowing only one image into each eye

http//www.3dglassesonline.com/how-do-3d-glasses-w
ork/index.html
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Law of Reflection
Angle of incidence is equal to angle of
reflection I incoming light N Normal R
Reflected light
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Reflected Light

• SPECULAR REFLECTION light is reflected in the
  same forward direction only
• DIFFUCE REFLECTION light is reflected in many
  directions

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Total Internal Reflection

• Occurs when light travels from a medium of larger
  to smaller index of refraction
• the light ray can actually bend so much that it
  never goes beyond the boundary between the two
  media

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Total Internal Reflection

• If the fish looks upwards it sees the sky, but if
  it looks at too large an angle to the vertical it
  sees the bottom of the pond reflected on the
  surface of the water.
• The critical angle to the vertical is equal to
  the critical angle for total internal reflection
  at an air-water interface which is approximately
  49.

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Total Internal Reflection
Refracted ray
http//www.glenbrook.k12.il.us/gbssci/phys/CLass/r
efrn/u14l3b.html
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Fiber Optics

• Fiber-optic lines are strands of optically pure
  glass as thin as a human hair
• The light in a fiber-optic cable travels through
  the core (hallway) by constantly bouncing from
  the cladding (mirror-lined walls)
• total internal reflection

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Refraction
http//fr.wikipedia.org/wiki/RC3A9fraction
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The Law of Refraction

• The law of refraction is used to predict the
  amount of bend, or refraction.
• The law of refraction is also known as Snell's
  Law, named for Willobrord Snell, who discovered
  the law in 1621.

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More on Refraction

• Assuming that the air on both sides of a window
  have the same refractive indices
• Then the incoming and outgoing light beams are
  actually parallel

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Snells Law
http//www.iop.org/activity/education/Teaching_Res
ources/Teaching20Advanced20Physics/Vibrations20
and20Waves/Reflection20and20refraction/page_447
7.html
The relationship between the angles of incidence
and refraction and the indices of refraction of
the two media involved.
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Bending Towards the Normal

• ex light passing from air into water
• lower to higher density
• the angle of refraction is smaller than the angle
  of incidence

http//id.mind.net/zona/mstm/physics/light/rayOpt
ics/refraction/refraction1.html
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Bending Away From the Normal

• ex light passing from water into air
• higher to lower density
• the angle of refraction is larger than the angle
  of incidence.

http//id.mind.net/zona/mstm/physics/light/rayOpt
ics/refraction/refraction1.html
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Examples of objects that create a Spectrum

• Prism
• Raindrops
• CDs
• Diffraction Grating
• The tracks of a compact disc act as a diffraction
  grating, producing a separation of the colors of
  white light

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• The color of light emitted by a hot object
  changes with its temperature.
• Glowing object colors
• Reddish ? coolest glowing object
• Orangeish
• Yellowish
• White
• Bluish ? hottest glowing object

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Transparent Materials

• object through which light can pass in straight
  lines

http//www.gcsescience.com/pwav21.htm
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Clear glass is transparent to visible light but
not to infrared light therefore trapped heat!
http//www.ucolick.org/bolte/AY4_00/week2/light_s
idetripsC.html
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Visible Light to Infrared

• Clear glass is transparent to Visible light.
• Absorbed, converted, emitted as Infrared.
• Clear glass is not transparent to Infrared Light.
• Trapped infrared light increases interior
  temperature.

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Opaque Materials

• Opaque - the term applied to materials that
  absorb light

http//www.ronbigelow.com/articles/color-perceptio
n-2/perception-2.htm
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Translucent Material

• Allows some light to pass through
• ex a filter or tinted glass

http//www.ronbigelow.com/articles/color-perceptio
n-2/perception-2-6.jpg
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Shadows

• Umbra - the darker part of a shadow where all the
  light is blocked
• Penumbra - a partial shadow

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Solar Eclipse
Umbra
Sun
Full Shadow
Earth
Moon
Partial Shadow
Penumbra

• A solar eclipse occurs when the Moon passes in
  front of the Sun.

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Lunar Eclipse
Sun
Earth
Moon

• A lunar eclipse occurs when the Moon passes into
  the Earth's shadow.