Light and the Electromagnetic Spectrum - PowerPoint PPT Presentation

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Light and the Electromagnetic Spectrum


Light and the Electromagnetic Spectrum Light Phenomenon Isaac Newton (1642-1727) believed light consisted of particles By 1900 most scientists believed that light ... – PowerPoint PPT presentation

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Title: Light and the Electromagnetic Spectrum

Light and the Electromagnetic Spectrum
Light Phenomenon
  • Isaac Newton (1642-1727) believed light consisted
    of particles
  • By 1900 most scientists believed that light
    behaved as a wave.

Light What is it?
  • Light Energy A special type of wave
  • Atoms
  • As atoms absorb energy, electrons jump out to a
    higher energy level
  • Electrons release light when falling down to the
    lower energy level
  • Photons bundles/packets of energy released when
    the electrons fall(they have no mass)
  • So, Light is a stream of photons

The Electromagnetic Spectrum
  • The electromagnetic spectrum represents the range
    of energy from low energy, low frequency radio
    waves with long wavelengths up to high energy,
    high frequency gamma waves with small

  • Visible light is a small portion of this
    spectrum. This is the only part of this energy
    range that our eyes can detect. What we see is a
    rainbow of colors.
  • RedOrangeYellowGreenBlueIndigoViolet

Frequency Ranges
  • Wavelengths
  • 104 101 1 10-2 10-5 10-6 10-8 10-10
  • Frequencies (cycles per sec)
  • 3 x 106 3 x 1010 3 x 1014 3 x 1016
    3 x1018 3 x10 22

Frequency Ranges of Visible Light
  • Red light has a frequency of roughly
  • 4.3 1014 Hz, and a wavelength of about 7.0
    107 m (700nm).
  • Violet light, at the other end of the visible
    range, has nearly double the frequency7.5 1014
    Hzand (since the speed of light is the same in
    either case) just over half the wavelength
  • 4.0 107 m (400nm).

Electromagnetic spectrum
  • Radio Waveslongest wavelength/lowest frequency
  • Infrared Rayslight rays w/longer wavelength than
    red light (ex cooking, tv remote, etc.)
  • UV Raysfrequencies higher than visible light
    (ex food processing, kill germs, helps
    w/vitamin D absorption)

Electromagnetic spectrum
  • X-Rays
  • Shorter than UV rays
  • Uses bones absorb x-rays soft tissue does not
  • Lead absorbs X-rays
  • Gamma Rays
  • highest frequency/shortest wavelength
  • Uses cancer treatment

  • The radiation to which our eyes are most
    sensitive has a wavelength near the middle of
    this range, at about
  • 5.5 x 10-7m (550 nm), in the yellow-green region
    of the spectrum.

  • It is no coincidence that this wavelength falls
    within the range of wavelengths at which the Sun
    emits most of its electromagnetic energyour eyes
    have evolved to take greatest advantage of the
    available light.

  • The colors we see in objects are the colors that
    are reflected, all other colors are absorbed. A
    red t-shirt appears red because red is reflected
    to our eyes and the other colors are absorbed.
  • When all colors are being reflected we see white
    light (white isnt really a color)

  • When all wavelengths of light are being absorbed
    we see black (black also, isnt really a color)
  • A false-color image is made when the satellite
    records data about brightness of the light waves
    reflecting off the Earth's surface.

  • These brightnesses are represented by numerical
    values - and these values can then be
    color-coded. It is just like painting by number.
  • The next slide shows a true color vs. false color
    image of the planet Uranus. Satellite images can
    be gathered in true color (what our eyes would
    see) and false color (to make it look better)

  • The true color image on left is how our eyes
    would see it.
  • The false color image is enhanced to bring out
    subtle details to make it easier to study Uranus
    cloud structure.

Light Refraction
  • Is bending of light due to a change in speed
    through an object (of light)
  • Index of Refraction-amount by which a material
    refracts light
  • Prisms-glass that bends light. Different
    frequencies are bent different amounts and light
    is broken out into different colors

Light Reflection
  • Bouncing back of light waves
  • Regular reflection-mirrors w/smooth surfaces
    scatter light very little/images are clear and
  • Diffuse reflectionreflected light is scattered
    due to an irregular surface

Light Diffraction
  • Bending of waves around the edge of a barrier.
    New waves are formed from the original.
  • Ex Diffraction glasses

Light and Its Uses
  • Optical Instruments
  • Lasers-
  • Stands for Light Amplification by Stimulated
    Emission of Radiation
  • Uses Coherent light-very powerful and intense
  • Holography
  • Fiber Optics
  • Communications, medicine, tv transmission, etc.

  • Opaque absorbs and reflects light-no light
    passes through it
  • Translucent allows some light to pass through,
    but you cannot see clearly through it
  • Transparenttransmits almost all of the light
    that strikes them-can see clearly through it
    (picture/pg. 420)
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