Conceptual Questions Chap' 22

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Conceptual Questions Chap. 22

• Why does the arc of a rainbow appear with red on
  top and violet on the bottom?
• Under what conditions is a mirage formed? On a
  hot day, what are we seeing when we observe a
  mirage water puddle on the road?
• The level of water in a clear, colorless glass is
  easily observed with the naked eye. The level of
  liquid helium (which has an index of refraction
  close to that of air) in a clear glass vessel is
  extremely difficult to see with the naked eye.
  Explain.
• Why does a diamond show flashes of color when
  observed under white light?

The spectrum of the light sent back to you from a
drop at the top of the rainbow arrives such that
the red light strikes the eye while the violet
light passes over your head. At the bottom of
the bow, violet light arrives at your eye and red
light is deviated toward the ground (see Figure
22.20).
A mirage occurs when light changes direction as
it moves between batches of air having different
indices of refraction, due to air having
different densities at different temperatures.
Two images are seen one from a direct path from
the object to you, and the second arriving by
rays originally heading toward the ground but
refracted to your eye. On a hot day, the Sun
makes the surface of blacktop hot, so the air is
hot directly above it, becoming cooler with
increasing altitude. The water we see is an
image of the blue sky. Shimmering occurs when
the air changes in temperature.
The index of refraction of water is quite
different from air, while the index of refraction
of liquid helium happens to be much closer to
that of air. Consequently, light undergoes less
refraction at the helium-air interface than it
does at the water-air one.
The diamond acts like a prism in dispersing the
light into its spectral components.