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Special Cases and Effects
- Objects under water: They appear to be at a higher location than they
really are (How can you show this with a drawing?), and so a
partially submerged object will look bent at the point where
it crosses the surface; [They also appear to be larger, but we
did not say very much about this fact in class].
- Position of the Sun: When it is near the horizon, the Sun appears to be
higher than it really is (How can you explain this with a drawing?).
- Mirages:
Exposure to the Sun causes the air near surfaces like a hot road
or desert surface to be hotter than the air higher up, and therefore
thinner; This speeds up the motion of light, and makes light
waves bend upward, producing on the surface fuzzy images of the
sky (that may look like water) or other objects (How can you
explain this with a drawing?).
- Dispersion:
The separation of colors in light that contains a combination
of wavelengths.
- What causes dispersion? The only thing we saw in this chapter that causes
it is refraction; Because blue light and red light travel at
different speeds in transparent materials, those colors are bent
by different amounts when there is refraction; In usual transparent
materials blue light moves slower than red light, because its
frequency matches better the electrons' motions frequencies,
so blue light is bent more.
- Rainbows:
By a combination of refraction and reflection, sunlight is bent
by small droplets of water suspended in the atmosphere; Because
of dispersion, light of different colors is bent by different
angles; As a result, we see blue light coming from droplets that
are lower than the ones from which we get red light. (How do
you explain this with drawings?)
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