The document explains why planets do not twinkle, attributing the effect to their proximity to Earth and their perception as extended light sources. It discusses atmospheric refraction's influence on the sunrise and sunset visibility, the scattering of light leading to red hues during these times, and the Tyndall effect which makes light paths visible in the atmosphere. Additionally, it addresses various phenomena related to light such as color scattering, reflection, and the formation of rainbows.

1. COLOURFUL
WORLD

2. - Why planets do not twinkle ?
- Planets are closer to earth and are seen as extended
source of light i.e. the collection of large number of
point sized sources of light.
- Therefore the total amount of light entering our eyes
from all individual point source will nullify the
twinkling effect.

3. Advance Sunlight and
Delayed Sunset
The sun is visible 2 minutes
before the actual sunrise or
sunset appears 2 minutes after
the actual sunset has taken
place is due to atmospheric
refraction.

4. • Apparent flattering of the Sun’s disc at sunset and
sunrise is due to atmospheric refraction.
• Scattering of light decreases with increase in
wavelength.

5. Color of Sunrise and Sunset:
- While sunset and sunrise, the colour of the sun and its
surrounding appear red.
- During sunset and sunrise, the sun is near to horizon,
and therefore, the sunlight has to travel larger
distance in atmosphere.
- Due to this, most of the blue light (shorter
wavelength) is scattered away by the particles. The
light of longer wavelength (red colour) reaches our
eye. This is why sun appear red in colour.

7. • Why the danger signal or sign is made of red
colour?
- Red colour scatteres the most when strikes the small
particle of fog and smoke because it has the maximum
wavelength (visible spectrum).
- Hence, from large distance also, we can see the red
colour clearly.

8. • Tyndall Effect:
- When a beam of light strikes, the minute particle of
earth’s atmosphere, suspended particles of dust and
molecule of air the path of beam become visible.
- The phenomenon of scattering of light by the colloidal
particle gives rise to Tyndall Effect.

9. - It can be observed when sunlight passes through a
canopy of a dense forest.
- The colour of the scattered light depends on the size of
the scattering particles.

10. Q1. When a beam of white light falls on a glass prism,
the colour of light which will deviate least is:
(a) Violet
(b) Red
(c) Green
(d) Blue

11. Q2. The star appear shifted from their actual position
due to the phenomenon of:
(a) Diffraction of light
(b) Scattering of light
(c) Refraction of light
(d) Reflection of light

12. Q3. Blue colour of the sky is due to the phenomenon of:
(a) Reflection of light
(b) Refraction of light
(c) Dispersion of light
(d) Scattering of light

13. Q4. Which of the following figures correctly represents
the passage of white light through prism?

14. Q5. At noon the sun appears white as
(a) light is least scattered.
(b) all the colours of the white light are scattered away.
(c) blue colour is scattered the most.
(d) red colour is scattered the most.

15. Q6. Which of the following phenomena of light are
involved in the formation of a rainbow?
(a) Reflection, refraction and dispersion
(b) Refraction, dispersion and total internal reflection
(c) Refraction, dispersion and internal reflection
(d) Dispersion, scattering and total internal reflection

16. Q7. The clear sky appears blue because
(а) blue light gets absorbed in the atmosphere.
(b) ultraviolet radiations are absorbed in the
atmosphere.
(c) violet and blue lights get scattered more than lights
of all other colours by the atmosphere.
(d) light of all other colours is scattered more than the
violet and blue colour lights by the atmosphere.

17. Q8. Twinkling of stars is due to atmospheric
(a) dispersion of light by water droplets
(b) refraction of light by different layers of varying
refractive indices
(c) scattering of light by dust particles
(d) internal reflection of light by clouds

18. Q9. The danger signals installed at the top of tall
buildings are red in colour. These can be easily seen
from a distance because among all other colours, the
red light
(a) is scattered the most by smoke or fog.
(b) is scattered the least by smoke or fog.
(c) is absorbed the most by smoke or fog.
(d) moves fastest in air.

19. Q10. Which of the following phenomena contributes
significantly to the reddish appearance of the sun
at sunrise or sunset?
(a) Dispersion of light
(b) Scattering of light
(c) Total internal reflection of light
(d) Reflection of light

20. Q11. The bluish colour of water in deep sea is due to
(a) the presence of algae and other plants found in water
(b) reflection of sky in water
(c) scattering of light
(d) absorption of light by the sea

21. Q12. In the following diagram, the path of a ray of light
passing through a glass prism is shown:
In this diagram the angle of incidence, the angle of
emergence and the angle of deviation respectively are
(select the correct option):
(a) X, R and T
(b) Y, Q and T
(c) X, Q and P
(d) Y, Q and P

22. Q13. The splitting of white light into its component
colours is called
(a) refraction
(b) reflation
(c) dispersion
(d) tyndall effect

23. Q14. Reason behind advance sunrise and delayed sunset
(a) atmospheric refraction
(b) total internal reflection
(c) dispersion
(d) reflection