Wonders
of light – part II
Q1. Fill in the blanks
1. The phenomenon of splitting of light
into its component colours is ____________ (dipersion)
2. Very fine particles mainly scatter
___________ light. (blue)
3. The phenomenon of change in the
___________ of light when it passes from one transparent medium to another is
refraction. (direction)
4. The refractive index depends upon the
___________ of propagation of light in different media. (relative speed)
Q2. Rewrite the following table in such a way that column 2
and column 3 matches column 1.
Column 1
|
Column 2
|
Column 3
|
Dispersion
|
Change in the direction of ray of light due to
change in medium.
|
Blue colour of the sky.
|
Scattering
|
Splitting of white light into component colours
|
Twinkling of stars.
|
Refraction
|
Deflection of light by small particles
|
Spectrum of seven colours.
|
Ans.
Column 1
|
Column 2
|
Column 3
|
Dispersion
|
Splitting of white light into component colours
|
Spectrum of seven colours.
|
Scattering
|
Deflection of light by small particles
|
Blue colour of the sky.
|
Refraction
|
Change in the direction of ray of light due to
change in medium.
|
Twinkling of stars.
|
Q3. Answer the followings.
1. What do you mean by dispersion? Name
the different colours of light in the proper sequence in the spectrum of light.
Ans.
i.
The
phenomenon of splitting of white light into its component colours is
dispersion.
ii.
The
various colours in the spectrum of light are in the sequence: Violet, indigo, Blue, Green, Yellow, Orange
and Red.
2. Explain how the formation of rainbow
occurs.
Ans.
1.
The
beautiful phenomenon of the rainbow is a combination of different phenomena –
dispersion, refraction and reflection of light.
2.
The
rainbow appears in the sky after a rain shower.
3.
The
water droplets act as a small prisms.
4.
When
sunlight enters the water droplets present in the atmosphere, they refract and
disperse the incident sunlight.
5.
Then
they reflect it internally inside the droplet and finally again refract it.
6.
As
a collective effect of all the phenomena, the seven coloured rainbow is
observed.
3. What is refraction of light? How is
it related to refractive index?
Ans.
i.
The
phenomenon of change in the direction of light when it passes from transparent
medium to another is called dispersion of light.
ii.
The
extent of change in the direction of the light ray is different for different
media and it is related to the refractive index of the medium.
Q4. Give reasons.
1. The sky appears dark instead of blue
to a person located in space.
Ans.
i.
At
very high altitudes, there is no atmosphere.
ii.
Since
there is no atmosphere, the scattering of light does not take place at all.
iii.
Hence,
the sky appears dark instead of blue to a person located in space.
2. Stars twinkle at night.
Ans.
i.
In
the atmosphere, there are different layers of air with different refractive
indices which keep on changing.
ii.
When
we observe the stars through this air the light coming from them refract
randomly so that the intensity of light varies due to which the apparent
position of the star fluctuates.
iii.
When
more light reaches our eyes the star is seen bright and when less light reaches
our eyes, the star is seen dim.
iv.
Thus,
due to change in refractive index of atmosphere, stars appear twinkling at
night.
3. The sun appears reddish early in the
morning.
Ans.
i.
At
the time of sunrise, the blue and violet colours are scattered away from the
path of sunlight as thickness of the atmosphere is more between the horizon and
the observer.
ii.
The
light that reaches to the observer is mostly red.
iii.
Hence
the sun appears reddish early in the morning.
4. It is possible to enjoy a rainbow at
fountains in any season.
Ans.
i.
One
can observe and enjoy the rainbow by standing in front of a water fountain in
the evening facing the east.
ii.
One
can also enjoy it in the morning under the same conditions just by facing the
west.
iii.
Therefore,
it is possible to enjoy a rainbow at fountains in any season.
Q5. Write short notes on
1. Refraction observed in the
atmosphere.
Ans.
i.
In
the atmosphere, there are different layers of air with different refractive
indices which keep on changing as the physical conditions of air are not
stationary (still).
ii.
When
we observe any object through this air, the light coming from them refract randomly
due to which the apparent position of the object fluctuates.
iii.
The
large scale effect of this phenomenon is the twinkling of stars, advanced
sunrise and delayed sunset.
iv.
Due
to change in the refractive index of atmosphere, the intensity of light that reaches
our eyes from the stars varies and hence the stars appear twinkling at night.
v.
Advanced
sunrise occurs as a ray of light from the sun enters the earth’s atmosphere; it
follows a curved path due to refraction before reaching to the observer.
vi.
It
appears to the observer as if the rays are coming from the position where the
sun is seen by the observer, hence, the sun is seen earlier before it reaches
the horizon.
2. Dispersion of light.
Ans.
i.
The
phenomenon of splitting of light into its component colours is dispersion of
light.
ii.
The
band of coloured components of a light beam is called it’s spectrum.
iii.
When
White light is dispersed into seven colours by a prism, different colours of
light bend through different angles with respect to incident ray.
iv.
Out
of these seven colours, red light bend the least while violet light bends the
most.
v.
So
the rays of each colour emerge along different paths and become distinct.
vi.
Hence
we get a spectrum of seven different colours in the sequence, Violet, Indigo,
Blue, Green, Yellow, Orange and Red.
