12.7 Natural Phenomena's

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12.7 Natural Phenomena's
A Phenomena ? an observable event or fact an
object or aspect known through the senses rather
than by thought or intuition. Nature has many
interesting phenomena involving light. We can use
our understanding of geometric optics to explain
many of these phenomena
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Apparent Depth

• Apparent depth is the depth that an object
  appears to be at due to the refraction of light
  in a transparent medium.
• Examples when looking at an object in water,
  it is apparent depth that gives us the optical
  illusion that the object is closer to the surface
  then it truly is.

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A Mirage

• A mirage can appear when light is travelling
  from cool air into warmer air. The index of
  refraction for air decreases as the air gets
  warmer. This results in the light bending farther
  away from the normal as the air temperature
  continues to increase.
• Eventually, total internal reflection occurs
  in the lowest(hottest) air layer. This light ray
  now travels up from the hottest layer to the
  cooler layer above and gradually refracted toward
  the normal as the air temperature decreases. Then
  the light ray eventually enters your eye.

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You see a false image of water on the road as it
seems to show a reflection of the surrounding sky
line.
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Mirages of the sky look like patches of water
but even when trees or distant hills are being
miraged, the impression of a water reflection can
be very striking.
MIRAGE water on the road
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The Flattened Sun
When the sun is close to the horizon, light from
the bottom of the sun is refracted more than the
light at the top of the sun. The air near the
earth s surface is more dense than the air
higher up in the atmosphere. So this change in
density causes the light rays to bend. Also,
the light at the bottom of the sun have a greater
angle of incidence than the rays coming off the
top of the sun. These two things combined give
the appearance that the sun is flat rather than
its normal round shape.
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Rays from the setting Sun (lower) are refracted
by the atmosphere and make it appear higher in
the sky.   The lower limb is lifted more than the
top, making its image oval, and flattened.
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The Rainbow

• In the previous section, we learned that white
  light can be separated into a continuous sequence
  of colours called the visible spectrum.
• Each colour of the visible spectrum travels at a
  different speed. This is evident when separated
  by a glass prism.
• Example- Violet light slows down more then red
  light. That is usually why we usually see more
  violet light as part of a rainbow.

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• A rainbow is produced by water droplets in the
  atmosphere.
• Refraction occurs when the light enters the water
  droplet from the air, resulting in the dispersion
  of the visible light.
• Partial internal reflection occurs when light
  hits the back of the rainbow.
• The light then refracts again as it goes from the
  water back into the air.
• You can only see a rainbow when the sun is behind
  you because your brain must project the suns
  rays back to your eyes to create a virtual image
  of the
• visible spectrum.

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HOMEWORK

• Read pages 535 -539
• ANSWER page 539 1, 2, 3, 4, 6