Aptitude Test Problems in Physics Science for Everyone by S Krotov ( PDFDrive.com )

Solutions

297

from the axis of tine pencil. For this reason, a large

dark spot is formed under <the pencil (Fig. 231).

When the pencil is drawn out of the water, the

water surface near the pencil forms a converging

Fig. 231

Fig. 232

lens: the rays emerging from the light source are
deflected towards the axis of the pencil. For this
reason, a bright spot is formed under the pencil
(Fig. 232).
4.7. The answer follows from Fig. 233. The first
bright ring is formed by the rays which undergo
one reflection from the body before they leave it
(such a ray is marked by 1). The second bright ring
is formed by the rays undergoing two reflections
(such a ray is marked by 2), and so on. Clearly,
the larger the number of reflections, the more the
light absorbed by the body of the ballpoint pen.
Therefore, the further a bright ring from the centre,
the lower its brightness.
4.8. Let us prove that after refraction all the rays
emerging from the point source towards the screen
will lie within the cylinder, and after multiple
reflections from the lateral surface of the cylinder,
will ultimately pass through the hole in the screen.
Indeed, the extreme ray from the point source S,
whose angle of incidence on the left base of the

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