the change of direction of a ray of light

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the change of direction of a ray of light as it
passes obliquely from one medium into another of
different transmission speed
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When light travels from a less dense to more
dense medium (light slows down), the ray is
refracted toward the normal.
Example light slows down when it passes from
air
into water
n
i
i
gt
r
air
water
r
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When light travels from a more dense medium to a
less dense medium (light speeds up), the ray is
refracted away from the normal.
Example light speeds up when passing from
glass into air
air
i
n
r
glass
i
r
lt
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An objects ability to decrease the speed of
light, and therefore cause refraction, is given
by its index of refraction.
The table to the left shows values of the index
of refraction for some common substances. The
larger the index of refraction, the slower that
light travels through the substance.
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LENS
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Converging Lenses - thicker in middle than in the
edge
Diverging Lenses - thicker at edge than in middle
concave
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Ray Diagrams
Converging Lenses
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Images formed by converging lenses may be 1.
real, virtual, or non-existent 2. upright or
inverted 3. reduced, enlarged, or same size 4. in
front or behind the lens
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The image characteristics depend on the objects
position with respect to one and two focal
lengths (1f and 2f) away from the lens.
2f
f
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object is beyond two focal lengths image is
real, inverted, and reduced
object is exactly twice the focal length image
is real, inverted, and the same size
object between one and two focal lengths image
is real, inverted, and enlarged
object is on the focus no image rays reflect
parallel
object is inside the focus image is virtual,
upright, and enlarged
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• General Image Trends
• real images are always inverted
• virtual images are always upright
• real images are always behind the lens
• virtual images are always in front
• of the lens
• negative image distance means
• virtual image
• positive image distance means real image
• real images may be projected onto a screen
  virtual images may not