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Properties of Light

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Title: Properties of Light


1
Properties of Light
2
Electromagnetic Waves
  • An electromagnetic wave is an oscillating
    combination of a magnetic and an electric field.
  • It can be visualized as two perpendicular waves
    (electric and magnetic).

3
Speed of Light
  • In a vacuum, all electromagnetic waves have a
    velocity of 300,000,000 m/s! ( 3x108m/s)

Thats 186,000 miles per second!
4
Electromagnetic Spectrum
  • An electromagnetic spectrum is a map of the
    total range of waves.

Usually, high frequency (low ?) is on the
right. Low frequency (high ?) is on the left.
5
  • Notice the wide range of waves. We only perceive
    visible light, a tiny fraction of the whole
    spectrum...

6
  • Sometimes an object may have a very different
    appearance depending on the wavelength of light
    you are using to observe it. Ex visible light
    and infrared picture of the constellation Orion

7
Historical attempts to explain light
  • Ancient idea
  • light emanates from eye to illuminate object
  • Newton (18th century)
  • light is particulate and moves faster in
    transparent materials
  • Young (1801)
  • interference experiments demonstrates wave nature
    of light
  • Einstein (early 20th century)
  • explains photoelectric effect by assuming a
    particulate nature of light (lumps of waves with
    E hf)

8
Known Properties of Light
  • Explained classically by Maxwells Equations (in
    1860)
  • Transverse Wave
  • polarization
  • Wave speed
  • speed of light in a vacuum
  • 3.00 108 m/s
  • speed of light slower in media
  • Particle (?)
  • the photon (E hf)

9
Dual Nature of Light
  •       Light exhibits wave phenomena as a light
    wave is propagated by interchange of energy
    between varying electric and magnetic fields
    (Maxwell)
  •       Light acts like particles composed of
    kinetic energy and momentum when light interacts
    with matter
  • Both wave and particle!

10
Wave Nature of Light
  • Wave Nature
  •       Light exhibits wave characteristics like
  • Diffraction bending around an obstacle
  • Interference adding subtracting energy
  • Doppler Effect change in frequency due to
    motion
  • Polarization - filtering
  • Particles are not able to do any of those
    characteristics

11
Polarization
(Source of light is excited atoms)
Plane polarized
Unpolarized
12
Methods of chararacterizing the light wave
  • ray construction
  • lines perpendicular to wavefronts showing
    direction of motion of wave
  • the plane wave

13
Polarizer-Analyzer
14
Particle Nature of Light
  • Particle Nature
  •         The Photoelectric Effect
  • Light having a frequency above some minimum value
    and incident on metals causes electrons to be
    emitted from the metal

Albert Einstein explained the phenomenon using
quantum theory developed by Max Planck
15
Transparent Materials
  • Transparent materials allow light to pass through
    in a straight line.

16
  • The explanation for why certain materials are
    transparent and others arent, depends on the
    atoms of the material and their vibrations.

17
  • When light hits a transparent material, it causes
    the atoms to vibrate only a little. The wave has
    very little energy lost to those vibrating atoms.
    The wave is free to pass through the transparent
    material.

18
Opaque Materials
  • An opaque material doesnt allow light to pass
    through it.
  • In this case, the light causes the atoms of the
    material to vibrate a great deal. This
    dissipates the energy of the wave, which cant
    pass through the material...

19
  • When light doesnt pass through an opaque object,
    it is absorbed. The energy of the wave is
    transferred into heat.

20
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21
  • Materials can be transparent to certain
    wavelengths, but not others..
  • For example, glass is transparent to visible
    light, but not to ultraviolet or infrared
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