Adv Physics

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Adv Physics

• Chapter 15
• Section 1

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Refraction

• Air
• water

• If wave strikes boundary at a right angle the
  wave continues in a straight line since all parts
  of the wave slow at the same time by the same
  amount

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Refraction

• Air
• water

• If wave strikes boundary at an angle the wave
  abruptly changes direction since part of the wave
  is slowed while part maintains its speed

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Refraction

• Bending of a wave as it passes from one medium to
  another have a different density and a different
  speed

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Refraction

• Inc ray reflected
• ray
• i r
• normal
• refracted
• ray

• Reflected light follows the law of reflection so
  i r
• If i gt 0 degrees then the transmitted part is
  refracted
• If i 0 degrees then the transmitted part
  travels straight through and is not refracted

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Refraction

• Water
• air

• If wave strikes the boundary at an angle the wave
  abruptly changes direction since part of the wave
  is sped up while part maintains its speed

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Refraction

• If you travel into a medium where you slow down,
  the light bends toward the normal and the angle
  gets smaller
• i gt refraction angle
• If you travel into a medium where you speed up,
  the light bends away from the normal and the
  angle gets bigger
• i lt refraction angle
• Exception! If i 0 degrees (travels along the
  normal) the light doesnt bend at all

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Index of Refraction

• Measure of lights speed in a medium
• Ratio of the speed of light in a vacuum to the
  speed of light in a medium
• n c / v
• where n index, c speed of light in vacuum,
  v speed of light in medium

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Index of Refraction

• Speed of light in water 2.25 x 108 m/s
• n c/v 3 x 108 / 2.25 x 108 1.333
• Speed of light in glass 2 x 108 m/s
• n c/v 3 x 108 / 2 x 108 1.5
• Note larger the value for n, the slower light
  travels in that medium

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Sample Problem

• The light emitted by a He-Ne laser has a
  frequency of 4.74 x 1014 Hz. Find the wavelength
  of the light in a vacuum and in ordinary crown
  glass.

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Snells Law

• When light travels from a material with index n1
  into a material with index n2, the angle of
  refraction, T2 is related to the angle of
  incidence, T1 by
• n1 sinT1 n2 sinT2

• T1
• n1
• n2
• T2

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Sample Problem

• A ray of light passes from air into water,
  striking at an angle of 25 degrees with the
  normal. The index of refraction of water is
  1.333. Calculate the angle of refraction of the
  ray of light.

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Sample Problem

• A light ray strikes an air/water surface at an
  angle of 46 degrees with respect to the normal.
  Find the angle of refraction when the direction
  of the ray is a) from air to water and b) from
  water to air.

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Sample Problem

• A light ray is incident on the outer surface of
  the cornea at an angle of 40 degrees with the
  normal. Find the angle the transmitted ray makes
  with the normal.

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Sample Problem

• A light ray passes from water into ice. If the
  transmitted ray makes an angle of 20 degrees with
  the normal, what is the angle of incidence.

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Sample Problem

• Light travels from air through a flat sheet of
  glass ( n 1.5 ) into water. If the angle of
  incidence in air is 30 degrees, what is the angle
  of the refracted ray in water?

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Sample Problem

• A light ray travels from air to water and then is
  reflected by a mirror under water. It strikes
  the mirror at an angle of 30 degrees. A) Find
  the angle of incidence as the ray enters the
  water. B) Find the angle of refraction as the
  ray leaves the water.