A very important class of waves

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A very important class of waves
electromagnetic waves

• Or Electromagnetic radiation
• A direct result of the interaction and connection
  between the electric field of charges and the
  magnetic fields produced when they
• MOVE

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Visible light

• The light that humans can detect is only a small
  part of the spectrum
• We humans can only see very few of the possible
  electromagnetic waves

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ELECTROMAGNETIC SPECTRUM

• All of the possible energies of electromagnetic
  radiation are arranged in order of increasing
  energy (decreasing wavelength)

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The Electromagnetic Spectrum
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Its all about WAVES

• Something oscillates, causing a wave
• When electrons oscillate,
• a time changing electric field is produced,
• which means a magnetic field is produced.
• The result is a

• traveling electromagnetic wave

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Traveling Electromagnetic wave
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Electromagnetic Wave Speed
"speed of light"

• Is the speed of ALL electromagnetic waves
• Is constant
• c ? 3 x 108 m/s
• ? 186,000 miles per SECOND
• (in a vacuum)
• Its the same for blue light, red light, radio
  waves, microwaves, x-rays, gamma rays,...

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So what does this mean?

• Are you OLDER or YOUNGER than the image you see
  when you look into the mirror??

OLDER!!It took time for the light from your real
face to travel to the mirror It took time for
the light to travel from the mirror to your
face So, the image you see is of the YOUNGER
you--it is how you looked prior to right now...
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EM Waves carry information

• By purposefully making modulations in either the
  amplitude or frequency of a traveling
  electromagnetic wave
• information can be encoded in the wave
• This information can b e transported from one
  place (the transmitter) to a distance place (the
  receiver)

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Modulation types

• Variation in the strength of the
  waveAMPLITUDE MODULATION
• Variation in the frequency of the waveFREQUENCY
  MODULATION

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The Ray approximationLight as a Particle

• We can describe the behavior of light waves by
  using a simple model
• We know that light travels in straight lines
  until it encounters some obstacle
• Light can be bent from its straight path by
• Refraction
• Reflection

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Light Interacting with a Material

• When light is incident upon a material, three
  things can happen
• The light can be reflected
• The light can be transmitted through the material
  (Refraction)
• The light can be absorbed by the material

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Light interacting with a material
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Refraction

• Occurs whenever a light ray goes from one
  material to another.
• Due to the changing speed of the light ray as it
  enters a new material.
• Depends on the energy of the light--this means it
  depends on the
• COLOR
• So, each color is refracted through a different
  angle

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REFRACTION

• ANYTIME light encounters an interface between two
  different media, REFLECTION and REFRACTION occur
• The amount of REFRACTION (the angle) depends on
  the WAVELENGTH of the light

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DISPERSION

• This is the phenomenon of the spreading
  outof the colors in light
• Common Example PRISM

White light in
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RAINBOW

• Based on the principle of dispersion, just like
  the prism you just saw
• LIGHT SOURCE SUN
• PRISM Small droplets of water
• Sun must be shining in one part of the sky, and
  water droplets must be falling in the opposite
  part of the sky

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Your own unique rainbow
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REFRACTION

• NOTE
• When the ray ENTERS THE GLASS, It is BENT
  TOWARD the normal
• When the ray ENTERS THE AIR (From the Glass), It
  is BENT AWAY from the normal

AIR
GLASS
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LENSES
CONVEX
CONCAVE
See it in the lab!!
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Lens properties

• A lens can either cause the rays to become closer
  together or further apart

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• Why is the Sky Blue??

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Why is the sky blue?
You already know that the atmosphere absorbs
most of the UV radiation from the
sun. Molecules of gas in the atmosphere
also SCATTER BLUE light This light has slightly
LOWER energy than the UV radiation
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Why is the sky blue?
This means that light is absorbed and then
re-emitted at the same frequency (same energy)

• SCATTERING
• OUR ATMOSPHERE
• 70 Nitrogen molecules

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What is important about N?

• NITROGEN MOLECULES VIBRATE WITH AN ENERGY
  EQUIVALENT TO THAT OF THE Visible blue to UV
  region of the EM spectrum
• VIOLET light is scattered most, followed by BLUE
• Even though violet dominates, our eyes do not see
  it as well, so we see the blue!!

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The blue sky
White light from the sun
scattering
All colors are scattered, BUT blue and violet are
scattered STRONGLY, so the blue and violet light
becomes more intense, and that is what we see
The result You look up and see a beautiful blue
sky!
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But Wait!, The sky isnt always blue...

• What about a magnificent red-orange sunset???

• Light of low frequency (energy) is scattered
  the
• least by nitrogen and oxygen molecules
• (this is the red, orange and yellow light)
• Red light is able travel the furthest distance
• through the atmosphere

SO, when white light (from the sun) passes
through a thicker atmosphere, the lower
frequency light makes it through!
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The path of sunlight
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Waves Summary

• Waves transport energy from one place to another
• Two main types transverse and longitudinal
• Waves are characterized by
• Frequency, period, amplitude, and wavelength
• The Doppler effect is the observed change in
  frequency of a source when there is relative
  motion between the observer and the source
• Resonance is when an object vibrates at its
  natural frequency
• Electromagnetic waves are transverse waves
  produced by the interaction of oscillating
  electric and magnetic fields

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Waves Summary (2)

• Radio waves can be used to transmit information
  by
• Amplitude modulation (AM)
• Frequency modulation (FM)
• All waves are observed to undergo
• Reflection, refraction, interference and
  diffraction
• The interaction of materials with light is
  characterized by the index of refraction
• A lens is an object used to redirect light
• Two types converging and diverging
• White light is composed of many different
  frequencies of light