61. Why are “blues” (NEER) added to clothes when washed?
When clothes are washed
frequently, they get scars and
discolorations, either due to
hard water phenomena or some
others. And the scars are
generally yellowish in color.
Among the "VIBGYOR" pattern of
the components of light,
yellowish color has to be
countered with bluish to
preserve its original white
color. So "blues" (NEER) is
added.
62. Why is the color of the sky blue?
When the sunlight passes through atmosphere, they are
scattered in all possible directions. The blue color is
scattered more than the other dispersed colors because
wavelength of blue light is minimum as compared to rest of
colors. When people look at the sky (not in the direction of
the Sun), the light ray
reaching the observer's eye
is the reflected or the
scattered one, never the
direct light coming from the
Sun. Such light is more
likely to possess light
radiations of the blue
group, rather than the red
or the yellow group. So, the color of the sky,
as it appears to the
observer is blue.
63. Why is the color of the sky reddish during sunset (in the
evening)?
This phenomena is more
observed more around the
region of the Sun or
when looking at the Sun
directly. When the
observer looks at the
Sun directly or looks at
the regions around it,
the light rays reaching
the person's eyes is
more or less the direct
light. The blue
color due to its high scattering capacity get dispersed and
get finished up from the
direct light, so can't reach the
observer. So, the color of the sky is reddish during sunset
(in the evening).
64. When white light passes through a flat piece of window glass
it is not broken down into colors as a prism does it. Explain
why?
When a ray
of light is passed through a prism it get dispersed because
the different colors of light are deviated in different
amount. But in case of a flat piece of window glass, the light
ray are only displaced but not deviated. Hence, light do not
get dispersed into its component colors. So, when the light is
passed through a flat piece of window glass it is not broken
down into colors as does by the prism.
65. Dispersion is caused by refraction but not by reflection.
Why?
This happens
because in
refraction light
radiations 'get
through' a
different medium
(i.e. a medium
of different
density),
whereas in
reflection,
radiations do
not even enter
the different
medium. When a light ray passes from one medium into another,
refraction takes place where the velocities of lights having
different wavelength are different so, they are deviated in
different amount. Hence a light ray is dispersed due to
refraction. But in the reflection phenomena, there is no change in
the medium by which a light ray do not get dispersed. Hence,
dispersion is cause by refraction but not by reflection.
66. What is the reason for dispersion of light?
The phenomenon of the splitting of white light into its
constituent colors, when the light ray is passed through a
prism is called "dispersion of light". When a ray of light is passed through a prism it gets
dispersed because the different colors of light are deviated
in different amount so they cannot be focused on the same
point and its constituent colors can be seen.
67. When a ray of white light is passed through a glass prism,
it is dispersed into different colors. But when it passes
through a rectangular glass slab no color is seen. Explain why?
When a ray of
light is passed through a glass prism it get dispersed because
the different colors of light are deviated in different
amount. But when it is passed through a rectangular glass slab
no color is seen as it behaves as combination of two prism of
same refractive index attached in opposite manner to each other.
When white light enters into a
rectangular glass slab, it is dispersed at the first face by
first prism. But at the second face of the prism, the dispersion
is
opposite
to
that
of the first face and equal in magnitude, so they cancel
each other and the light emerging from second face of slab is
white. Hence, when a ray of white light is passed through a glass
prism, it is dispersed into different colors. But when it
passes through a rectangular glass slab no color is seen.
68. Why is fluorescent tube light considered better than
tungsten filament bulb?
As the maximum
current energy is change into light energy in the
fluorescent tube light than the tungsten filament (where the
other energy is lost in the form of heat due to high
resistivity), the fluorescent tube light gives more
efficiency of light than tungsten filament i.e. electricity
is wasted in the form of heat in tungsten filament. Hence,
fluorescent tube light is considered better than tungsten
filament bulb. (In a tungsten lamp, light is the result of
excessive
heating,
so heat
is
produced
first,
then
light.
69.
70. Why does a photographer use a red bulb in his dark room?
Red light has larger wavelength and so less frequency. Therefore it is scattered very less. When a photographer is in the dark room, the negatives should not As
the red light scatters less as compared to other colors
because its wavelength is maximum,
71. Why a 100 W bulb appears brighter than the 40W bulb placed at
the same distance?
The luminous
efficiency of a 100 W bulb is greater than that of 40 W bulb.
So, 100 W bulb gives more luminosity than 40 W bulb. This is
the main reason behind the glowing of 100 W bulb more
brightly than 40 W bulb placed at the same distance.
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