- Optics 101
(during the adjustment, the eyepiece is
displaced relative to the objective).
What is the smallest possible distance a
from the objective starting from which
remote objects can be viewed by an un-
strained normal eye through this telescope?
4.5. Can a diverging lens be used to in-
crease the illuminance of some regions on
the surface of a screen?
4.6. A point light source is exactly above
a pencil erected vertically over the water
surface. The umbra of the pencil can be
seen at the bottom of the vessel with water.
If the pencil is immersed in water, the size
of the dark spot at the bottom increases.When the pencil is drawn out of water, a
bright spot appears instead of the dark one.
Explain the described phenomena.
4.7. If an illuminated surface is viewed
through the wide hole in the body of a ball-
point pen, several concentric dark and
bright rings are seen around the narrow hole
in the body.
Explain why these rings are observed.4.8. A point light source S is at a distance
l= 1 m from a screen. A hole of diameter
d = 1 cm, which lets the light through, is
made in the screen in front of the light
source. A transparent cylinder is arranged
between the source and the screen (Fig. 118).The refractive index of the cylinder materi-
al is n = 1.5, the cylinder length is 1 = 1 m,
and the diameter is the same as that of the