Bukhovtsev-et-al-Problems-in-Elementary-Physics

140 PROBLEMS
W 689. Two flat mirrors AO
~ and OB form a dihedral angle
A • q> =-; ~ were h n IS · an ·t In e-
• B ger. A point source of light
S is placed between the mirrors
at the same distance from
both of them. Find the num-
~~~~~~~~~~~~ her of images of the source
in the mirrors.
Fig. 241
690. Two flat mirrors AOand
OB form an arbitrary dihedral
angle cp = 2n, where a is any number greater than 2. A point
a
source of light S is between the mirrors at equal distances from
them. Find the number of images of the source in the mirrors.
691. In what direction should a beam of light be sent from
point A (Fig. 241) contained in a mirror box for it to fall onto
point B after being reflected once from all four walls?
Points A and B are in one plane perpendicular to the walls
of the box (i.e., in the plane of the drawing).
692. Why does the water seem much darker directly below an
airplane flying over a sea than at the horizon?
693. Over what distance will a beam passing through a planeparallel
plate be displaced if the thickness of the plate is d,
the refraction Index is n and the angle of incidence is i?
Can the beam be displaced by more than the thickness of the
plate?
n
A
A _--6--___.
c........_ .....---......a
Fig. 242
Fig. 243
C ----