Conceptual Questions Chap. 23

1
Conceptual Questions Chap. 23

1. Can a virtual image be photographed? Why or why
   not?
2. Why does a clear stream always appear to be
   shallower than it actually is?
3. Lenses used in eyeglasses, whether converging or
   diverging, are always designed such that the
   middle of the lens curves away from the eye.
   Why?
4. A common mirage is formed when the air gets
   gradually cooler as the height above the ground
   increases. What might happen if the air grows
   gradually warmer as the height is increased?

A virtual image can be photographed as any object
can. Light rays diverge from the position of a
virtual image just as they do from an actual
object.
Light rays from an object at the bottom of the
stream are refracted away from the normal to the
airwater interface. The resulting refracted
rays appear to originate from a point that is
closer to the surface than the object that emits
them really is.
The design is chosen so your eyelashes will not
brush against the glass as you blink. Also, when
you direct your gaze near the outer circumference
of the lens you receive a ray that has passed
through the glass with more nearly parallel
surfaces of entry and exit. Then the lens
minimally distorts the direction to the object
you are looking at.
An effect similar to a mirage is produced, except
the mirage is seen hovering in the air.
Ghost lighthouses in the sky have been seen
over bodies of water by this effect.