Sound

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Sound Light Ch. 3The Nature of Light Waves

• Section 3 Interactions of Light Waves

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Objectives

• Describe how reflection allows you to see things.
• Describe absorption and scattering.
• Explain how refraction can create optical
  illusions and separate white light into colors.
• Explain the relationship between diffraction and
  wavelength.
• Compare constructive and destructive
  interference of light.

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Reflection
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ReflectionThe Law of Reflection

• Reflection happens when light waves bounce off an
  object. Light reflects off objects all around
  you.
• The Law of Reflection states that the angle of
  incidence is equal to the angle of reflection.
• Law of Reflection visual

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ReflectionTypes of Reflection

• You see your image in a mirror because of regular
  reflection.
• Regular reflection happens when light reflects
  off a very smooth surface. All the light beams
  bouncing off a smooth surface are reflected at
  the same angle.

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ReflectionTypes of Reflection

• You cannot see your image in a wall because of
  diffuse reflection.
• Diffuse reflection happens when light reflects
  off a rough surface, such as a wall. Light beams
  that hit a rough surface reflect at many
  different angles.

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Reflection Light Source or Reflection?

• The tail of a firefly, flames, light bulbs, and
  the sun are light sources. You can see a light
  source in the dark because its light passes
  directly into your eyes.
• Most things around you are not light sources. But
  you can see them because light from light sources
  reflects off the objects and the travels to your
  eyes

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Absorption and Scattering Absorption of Light

• The transfer of energy carried by light waves is
  called absorption.
• When a beam of light shines through the air,
  particles in the air absorb some of the lights
  energy. As a result, the beam of light becomes
  dim.

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Absorption and Scattering Scattering of Light

• An interaction of light with matter that causes
  light to change direction is scattering.
• Light scatters in all directions after colliding
  with particles of matter.
• Light can be scattered out of a beam by air
  particles. This scattered light allows you to see
  things outside of the beam. But, the beam becomes
  dimmer because light is scattered out of it.

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Refraction
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Refraction

• Refraction is the bending of a wave as it passes
  at an angle from one material to another.
• Refraction of light waves occurs because the
  speed of light varies depending on the material
  through which the waves are traveling.
• When a wave enters a new material at an angle,
  the part of the wave that enters first begins
  traveling at a different speed from that of the
  rest of the wave.

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Refraction
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Refraction Refraction and Optical Illusions

• Your brain always interprets light as traveling
  in straight lines.
• But when you look at an object that is
  underwater, the light reflecting off the object
  does not travel in a straight line. Instead, it
  refracts.

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Refraction Refraction and Optical Illusions

• Because of refraction, the cat and the fish see
  optical illusions.

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Refraction Refraction and Color Separation

• White light is composed of all the wavelengths of
  visible light. The different wavelengths of
  visible light are seen by humans as different
  colors.
• When white light is refracted, the amount that
  the light bends depends on its wavelength.

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Refraction Refraction and Color Separation

• Waves with short wavelengths bend more than waves
  with long wavelengths.
• White light can be separated into different
  colors during refraction, as shown below.

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Diffraction

• Diffraction is the bending of waves around
  barriers or through openings.
• The amount a wave diffracts depends on its
  wavelength and the size of the barrier or opening.

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Diffraction and Wavelength

• The wavelength of visible light is very small.
• So, a visible light wave cannot diffract very
  much unless it passes through a narrow opening,
  around sharp edges, or around a small barrier.

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Interference

• Interference is the combination of two or more
  waves that results in a single wave.
• The new wave can be greater or weaker in
  strength.

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Interference

• The image below shows what happens when light
  combines by interference.