Fig. 120- Optics 105
4.16. A glass porthole is made at the bottom
of a ship for observing sealife. The hole
diameter D = 40 cm is much larger than
the thickness of the glass.Determine the area S of the field of vi-
sion at the sea bottom for the porthole if
the refractive index of water is n, = 1.4,
and the sea depth is h = 5 m.
4.17*. Let us suppose that a person seating
opposite to you at the table wears glasses.
Can you determine whether he is short-
sighted or long-sighted? Naturally, being
a polite person, you would not ask him to
let you try his glasses and in general would
make no mention of them.
4.18. A person walks at a velocity v in a
straight line forming an angle a with the
plane of a mirror.
Determine the velocity vā at i which he
approaches his image, assuming that the
object and its image are symmetric rela-
tive to the plane of the mirror.
4.19. Two rays are incident on a spherical
mirror of radius R = 5 cm parallel to its
optical axis at distances h 1 = 0.5 cm and
ha = 3 cm.