CHAPTER 14 REFRACTION

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CHAPTER 14 REFRACTION

• Section 14.1
• Refraction

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WHAT IS REFRACTION?

• Refraction bending of light at a boundary
  between 2 media.
• Optically dense speed of light in 1 medium is
  slower than another.
• Willebrord Snell (1621) studied the relationship
  between the angle of incidence and the angle of
  refraction (bending).

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SNELLS LAW

• A ray of light bends in such a way that the ratio
  of the sine of the angle of incidence to the sine
  of the angle of refraction is constant (Snells
  Law).
• When a ray of light travels from a vacuum to
  another medium, the formula is
• n sin ?i n is the index of
• sin ?r refraction (see pg. 490)

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SNELLS LAW CONT

• When a ray of light travels from one medium to
  another medium, the formula is
• ni sin ?i nr sin ?r
• See pg. 490 for n values

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REFRACTION DIAGRAM
incident ray
medium 1
angle of incidence Ti
medium 2
Tr angle of refraction
This is the normal
refracted ray
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VELOCITY AND REFRACTION

• It is possible to determine the index of
  refraction of an unknown object or the speed of
  light in that object using the following formula
  ns c
• vs

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CHAPTER 14 REFRACTION

• SECTION 14.2
• Thin Lenses

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TYPES OF LENSES

• A lens is a transparent material with a index of
  refraction gt air.
• A lens has 2 faces that are part of a sphere.
• There are two types of lenses convex and
  concave.

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CONVEX LENSES

• Convex lens called converging since it is
  thicker in the center than at the edges.
• The image produced from this type of lens can be
  either real or virtual, erect or inverted,
  enlarged or small. It depends on where the
  object is with respect to the focal point.

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MORE ON CONVEX LENSES

• If the object is located more than twice the
  distance from the focal point (2F), then the
  image is real, inverted, and small.
• If the object is located between F and 2F, then
  the image is real, inverted, and enlarged.
• If the object is in front of the focal point,
  then the image is virtual, erect, and enlarged.

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CONCAVE LENSES

• Concave lens called diverging because it is
  thinner in the middle than at the edges.
• Images produced from this lens are always
  virtual, erect, and smaller.

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USES OF MIRRORS LENSES

• Lenses are used to correct defects in the eyes.
• Farsightedness inability to see near objects so
  we use a converging (convex) lens.
• Nearsightedness- inability to see far objects so
  we use a diverging (concave) lens.

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MORE USES OF MIRRORS LENSES

• Microscopes allow us to see very small objects.
• It uses at least 2 convex lenses.
• The objective lens has a short focal length which
  produces a real image located between the
  eyepiece and the focal length.

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STILL MORE USES OF LENSES

• A telescope is designed to increase the angle
  between the rays from 2 different stars and to
  collect more light than the eye would see, not to
  magnify an image.
• It also uses 2 convex lenses.
• The objective lens has a long focal length which
  focuses the light rays from a distant object.

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STILL MORE USES OF LENSES

• The eyepiece has a short focal length that
  refracts these rays to produce a virtual,
  enlarged, inverted image.

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CHAPTER 14 REFRACTION

• Section 14.3
• Optical Phenomena

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TOTAL INTERNAL REFLECTION

• Occurs when the angle of refraction gt the angle
  of incidence.
• Occurs when a light ray travels from a more
  optically dense medium to a less optically dense
  medium.
• The angle that causes the refracted ray to lie
  right on the boundary is the critical angle.

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MORE ON TOTAL INTERNAL REFLECTION

• When the angle of refraction is gt than the
  critical angle, total reflection occurs.
• You can calculate the critical angle using the
  formula
• Sin ?c 1 where ?c is the
• ni critical angle

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LENS ABERRATIONS

• All optical instruments use achromatic lenses.
  These are designed to reduce the ring of color
  that is produced from a single lens. This
  phenomenon is called chromatic aberration.
• Spherical mirrors produce spherical aberration
  which is the inability of a mirror to focus light
  rays to a single point. This is why parabolic
  mirrors are used in flashlights, headlights, and
  search lights.