Solutions (^307)
where no is the refractive index of glass. Since
I sin a I <1/no, I sin 13 I< 1/nw. Therefore, the
observer can see only the objects emitting light
to the porthole at an angle of incidence
arcsin (1/nw). Figure 242 shows that the radius
of a circle at the sea bottom which is accessible to
observation is R h tan 11, and the sought area
(h. tan (3> D/2) is
h 2
S R 2 82 ma.
n
It
w 2 —1
4.17*. Short-sighted persons use concave (diverg-
ing) glasses which reduce the focal power of their
eyes, while long-sighted persons use convex (con-
verging) glasses. It is clear that behind a diverging
lens, the eye will look smaller, and behind a con-
verging lens larger. If, however, you have never
seen your companion without glasses, it is very
difficult to say whether his eyes are magnified or
reduced, especially if the glasses are not very strong.
The easiest way is to determine the displacement
of the visible contour of the face behind the glasses
relative to other parts of the face: if it is displaced
inwards, the lenses are diverging, and your com-
panion is short-sighted, if it is displaced outwards,
the lenses are converging, and the person is long-
sighted.
soomview
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