Ch. 17 Reflection and Refraction

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Ch. 17 Reflection and Refraction

• Milbank High School

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Sec. 17.1How Light Behaves at a Boundary

• Objectives
• Explain the law of reflection
• Distinguish between diffuse and regular
  reflection and provide examples
• Calculate the index of refraction in a medium

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The Law of Reflection

• Smooth Surfaces
• Mirrors
• Angle of incidence angle of reflection
• Seemingly smooth surfaces
• Walls
• Paper
• Actually rough surfaces
• Light waves result in diffuse reflection

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Refraction of Light

• Refraction
• Change in direction or bending of light at the
  boundary of two media
• Plastics, glass
• Optically dense materials
• If angle of refraction is smaller than the angle
  of incidence

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Snells Law

• The degree of refraction depends on angle of
  incidence and properties of the medium
• Snells Law
• Ratio of the sine of the angle of incidence to
  the sine of the angle of refraction is a constant

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Index of Refraction and the Speed of Light

• Index of refraction
• Measure of how much light bends in a new medium
• It bends because of a change in speed
• Index of refraction
• nsubstance c/vsubstance

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Review Questions

• Could the index of refraction ever be less that
  1?
• What behaviors does light exhibit?

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Sec. 17.2Applications of Reflected and Refracted
Light

• Objectives
• Explain total internal reflection
• Define the critical angle
• Explain effects caused by the refraction of light
  in a medium with varying refractive indices
• Explain dispersion of light in terms of the index
  of refraction

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Total Internal Reflection

• Occurs when light passes from a more optically
  dense medium to a less optically dense medium at
  an angle so great that there is no refracted ray
• Critical angle
• The incident angle that causes the refracted ray
  to lie right along the boundary of the substance,
  angle Tc
• sin Tc nr/ni

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Effects of Refraction

• Mirages
• Index of refraction changes in hot air vs. cool
  air
• Sunlight after the sun has set
• Index of refraction changes due to the change in
  density of the atmosphere

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Dispersion of Light

• Separation of light into its spectrum
• Happens as light travels through a prism
• Glass
• Diamonds
• Water
• Red bent the least
• Violet bent the most

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Rainbows

• Spectrum formed when sunlight is dispersed by
  water droplets in the atmosphere
• In afternoon, only see rainbows to the east