Pearson Prentice Hall Physical Science: Concepts in Action

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Pearson Prentice Hall Physical Science Concepts
in Action

• Chapter 18
• The Electromagnetic Spectrum and Light

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18.1 Electromagnetic Waves

• Objectives
• 1. Describe the characteristics of
  electromagnetic waves in a vacuum
• 2. Calculate the wavelength and frequency of an
  electromagnetic wave
• 3. Describe the evidence for the dual nature of
  electromagnetic radiation
• 4. Describe how the intensity of light changes
  with distance from a light source

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Characteristics of EM Waves

• Def electromagnetic waves are transverse waves
  consisting of changing electric fields and
  changing magnetic fields
• Def an electric field is a region of space that
  exerts electric forces on charged particles
• Def a magnetic field is a region of space that
  produces magnetic forces
• Magnetic forces are produced by magnets, changing
  electric fields and vibrating charges

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• EM waves can travel through a vacuum as well as
  through matter
• Def EM radiation is the transfer of energy by EM
  waves traveling through matter or across space
• Light and all EM waves travel at the same speed
  but the wavelength (?) frequency (f) can differ
• The speed of light ( all EM waves) is 3.00 x 108
  m/s

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Calculations

• Speed wavelength x frequency
• For EM waves, speed 3.0 x 108 m/s
• Frequency speed/wavelength OR f c/?
• Wavelength speed/frequency OR ?c/f
• The units for speed (c) are m/s
• The unit for wavelength (?) is m
• The unit for frequency (f) is Hz (1/seconds)

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EM Radiation/ Light Intensity

• EM radiation sometimes behaves like a wave and
  sometimes like a particle
• Light, therefore, is classified both as an EM
  wave and as a particle
• Def a photon is an EM packet of energy
• Each photons energy is proportional to the
  frequency of the light
• The intensity of light decreases as photons
  travel farther from the source

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18.2 The Electromagnetic Spectrum

• Objectives
• 1. Rank and classify EM waves based on their f
  (frequency) and ? (wavelength)
• 2. Describe the uses for different waves of the
  EM spectrum

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Rank and Classify

• The prism separates the wavelengths present in
  sunlight which is visible light
• From longest to shortest ROY G B(I)V
• The electromagnetic spectrum includes visible
  plus invisible radiation
• Increasing frequency from left to right (longest
  to shortest) radio waves, infrared rays, visible
  light, UV ray, X rays, and gamma rays

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Uses for EM Waves

• Radio waves are used in radio, television,
  microwaves and radar
• The shortest radio waves are microwaves
• Radar is an acronym radio detection and ranging
• Radar often uses the Doppler effect to determine
  how fast something is moving
• Infrared rays are used as a source of heat to
  discover areas of heat difference

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• Thermograms use infrared to sensors to show
  differences in temperature of objects
• Visible light is used to see, stay safe and
  communicate
• UV rays are used in health, medicine and
  agriculture
• X rays are used in medicine, industry and
  transportation to make pictures of the inside of
  solid objects
• Gamma rays are used medically to kill cancer
  cells, make brain pictures and in certain
  industrial situations such as checking pipelines
  for cracks or other damage

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18.3 Behavior of Light

• Objectives
• 1. Describe three types of materials that affect
  the behavior of light
• 2. Explain how light behaves when it enters a new
  medium

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Three Types of Materials

• The behavior of light is affected by transparent,
  translucent and opaque materials
• Transparent materials transmits light, allowing
  most light to pass through it
• Translucent material scatters light
• Opaque material either absorbs or reflects all
  the light that strikes it
• No light passes through opaque materials

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How Light Behaves

• When light strikes a new medium, the light can be
  reflected, absorbed or transmitted
• When light is transmitted, it can be refracted,
  polarized or scattered
• Def an image is a copy of an object formed by
  reflected light waves
• Def regular reflection is parallel light waves
  striking a surface and reflecting all in the same
  direction

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• Def diffuse reflection is parallel light waves
  striking a rough, uneven surface, reflecting in
  many directions
• Def refraction is the bending of light waves
• Def a mirage is a false, distorted image
• Mirages occur due to light traveling faster in
  hot air than in cool air
• It is a form of refraction
• Def polarization is light with waves that
  vibrate only in one direction
• Def scattering is light redirect as it passes
  through a medium