The comprehensive approach in Kerala Syllabus 9th Standard Physics Notes Pdf Chapter 1 Refraction of Light Notes Extra Questions and Answers ensures conceptual clarity.
Kerala Syllabus Std 9 Physics Chapter 1 Refraction of Light Extra Questions and Answers
Question 1.
Write examples for atmospheric refraction.
Answer:
Even after the sun has passed the western horizon, the Sun is visible for some more time. The Sun can be seen a few seconds before it reaches the eastern horizon in the morning.
– Twinkling of stars.
Question 2.
Four students traced the path of a light beam coming from air passing through a rectangular glass slab, and their names are A, B, C, and D in Figure. Which of these is correct?
Answer:
B
Question 3.
Choose the wrong statements from the following and correct it.
(a) We can see the apparent position of the Sun just before and just after the actual Sunrise and actual Sunset due to atmospheric refraction.
(b) The bottom of a pond appears lowered when viewed from a distance than from a nearer point.
(c) A ray incident normally at the surface of separation of mediums undergo refraction.
(d) As refractive index increases, speed of light decreases.
Answer:
(b) is a wrong statement
Corrected statement : The bottom of a pond appears elevated when viewed from a distance than from a nearer point
(c) is a wrong statement
Corrected statement: A ray incident normally at the surface of separation of mediums undergoes no refraction.
Question 4.
From the given statements choose the incorrect statements and correct it.
(a) At critical angle, the light ray instead of undergoing refraction, totally reflects back to the same medium.
(b) Optical fibres are used in the medical field.
(c) The critical angle of glass is lower than water because of the low refractive index of glass compared to water.
(d) If the angle of incidence is increased beyond the critical angle, total internal reflection takes place.
Answer:
(a) is incorrect
Corrected statement : At critical angle, the light ray passes through the boundary of the two mediums.
(c) is incorrect
The critical angle of glass is lower than water because of the high refractive index of glass compared to water.Critical angle is inversely proportional to refractive index of a medium.
Question 5.
During a physics class, teacher shown a laser pointer into a fish tank full of water in and it was noticed that the light beam reflects off the surface of water instead of going through it at a specific angle. What kind of phenomenon are you seeing, and what causes it to occur?
Answer:
This is due to total internal reflection. When the laser light hits the water-air boundary at an angle greater than the critical angle, it reflects entirely back into the water instead of refracting into the air.
Question 6.
Match the following.
| Stars twinkle | Total internal reflection |
| Mirage | Reflection |
| Brilliance of diamond | Atmospheric refraction |
| – | Refraction and total internal reflection |
Answer:
| Stars twinkle | Atmospheric refraction |
| Mirage | Refraction and total internal reflection |
| Brilliance of diamond | Total internal reflection |
Question 7.
Write the following pairs of media in descending order of their optical density. water, diamond, air, glass
Answer:
diamond > glass > water > air
Question 8.
Write the following pairs of media in descending order based on the speed of light through them- water, diamond, air, glass
Answer:
air > water > glass > diamond
Question 9.
The speed of light is……………. in different mediums. Choose the appropriate ward from bracket (same, different)
Answer:
different
Question 10.
The path of light will be in ………. when it passes through only one medium.
Answer:
a straight line
Question 11.
The figure given below shows a ray of light passing through two different media. Choose the correct image from the following?
Answer:
Picture 3.
When a ray of light passes from a medium of higher optical density to a medium of lower optical density the, refracted ray deviates away from the normal.
Question 12.
Which is the correct figure?
Answer:
(b)
When a ray of light passes from a medium of lower optical density (air) to a medium of higher optical density (water) the refracted ray deviates towards the normal.
Question 13.
Speed of light in a medium having low optical density will be ……..
Answer:
Greater
Question 14.
List the statements given below as true and false.
a) When light enters from an optically rarer medium to a denser medium, it deviates towards the normal.
b) When light enters from an optically denser medium to a rarer medium, it deviates towards the normal.
c) A ray incident normally at the surface of the separation of mediums does not undergo refraction.
d) The path of light will be in a straight line. when it passes obliquely from one medium to other.
Answer:
a) True
b) False
c) True
d) False
Question 15.
Rohan saw that his pencil seemed to be broken when dipped in a glass of water.
a) If he used kerosene instead of water, what change occurs there?
b) What is the reason?
Answer:
a) The pencil appears to be bent more.
b) The refractive index of kerosene is more than water.
Question 16.
Refractive index of glass is 1.5. If the speed of light in vacuum is 3 × 108 m/s, find speed of light in glass.
Answer:
Refractive index of glass. n = 1.5
Speed of light in vacuum = 3 × 108 m/s
speed of light in glass v = \(\frac{c}{n}\)
V = \(\frac{3 \times 10^8}{1.5}\)
v = 2 × 108 m/s
Question 17.
Light falls obliquely from one medium to another is shown in the figure. [MN is the normal at the point of incidence]
Which of the given medium is the fastest medium for light? Justify your answer.
Answer:
Medium A
Reason: From the figure. the angle of incidence is greater than the angle of refraction.When optical density decreases light ray will move assay from the normal. So. medium A has low optical density.
As optical density decreases, speed of light through the medium increases.
Question 18.
Speed of light in three media are given.
[Glass – 2 × 108 m/s. Water – 2.25 × 108 m/s
Diamond -1.25 × 108 m/s]
(a) In which medium does the refraction of light occurs more while falling from air?
(b) Arrange the three given media in the increasing order of optical density.
Answer:
(a) Diamond
(The speed of light in diamond is comparatively less because light undergoes higher refraction)
(b) Water < glass < Diamond
Question 19.
The refractive index of diamond is 2.42. What do you mean by this? Calculate the speed of light through diamond.
Answer:
Light travels through air with a velocity 2.42 times the velocity of light through diamond.
v = \(\frac{c}{n}\) = \(\frac{3 \times 10^8}{2.42}\) = 1.24 × 108 m/s
Question 20.
A ray of light travels from air to glass slab is depicted below. Observe figure and answer the questions.
a) Find out the incident ray?
b) Find out the refracted ray?
c) Which is the angle of incidence?
d)Which is the angle of refraction?
e) What happens when a ray of light obliquely travel from air to glass slab?
f) Name his phenomenon of light?
Answer:
a) PQ
b) QR
C) 30°
d) 90°
e) It bend towards the normal (refraction takes place)
f) Refraction
Question 21.
Raju placed a pencil in a trough of water as shown in figure.
a) Can you see a change in the position of the portion of the pencil underwater?
b) Does the ray of light coming after reflection from the pencil undergo a deviation? Why is it so?
Answer:
a) Refraction
b) Yes They ray of light from the immersed part of the pencil entering air from water is deviated at the surface of separation.
Question 22.
Why do stars appear to twinkle?
Answer:
The light coming from the stars reaches our eyes by traversing through the atmosphere. The optical density of the medium through which the light travels goes on changing the physical conditions (pressure, temperature etc.) of the layers of the atmosphere change continuously. Hence, the light undergoes an irregular refraction. Therefore. when the light rays from the stars reach the eyes after refracted several limes, the star cannot be seen continuously at the same position. This is the reason for the twinkling of stars.
Question 23.
Observe the figure. A ray of light enters from medium 1 to medium 2
(a) Find out which medium has greater optical density.
(b) Which medium has the greater refractive index?
(c) What is the relation between optical density and refractive index of a medium?
Answer:
(a) Medium – 1
(b) Medium – 1
(e) As the refractive index ofa medium increases, optical density also increases.
Question 24.
Appu and Ammu went for bow fishing on a holiday. Their opinions about how to catch the fish is given below.
Appu : One should aim at a point below the perceived position of fish
Ammu : One should aim at the exactly at the perceived position of the fish.
Who is correct. Justify your answer.
Answer:
Appu is correct.
When the reflected light coming from the fish enters from an optically denser medium(here water) to a rarer medium(air), it is deviated away from the normal, at the surface of separation. This refracted Light appears to come from a position just above the actual position.This is why it is advised to aim at a point below the perceived position of fish.
Question 25.
Given below are the different figures in which light passes obliquely from one medium to the other. AB is the normal.
a) Which of the figures indicates the path of the light ray which passes from air to water?
b) What is the reason for choosing this figure as the answer?
c) Which of the figures indicates the path of light ray which passes from glass to water?
d) In these figures, which one is wrong?
Answer:
a) i)
b) When light ray obliquely passes from rarer to denser, it bends towards normal.
c) iii)
d) ii)
Question 26.
Observe the figure. Light falling on two different media are shown.
a) Which medium has greater optical density? Through which medium will light pass through higher speed?
b) Why?
c) Which medium has greater refractive index
d) What do you mean by refractive index of a medium?
Answer:
a) Medium 2 has greater optical density. Through medium I light passes with higher speed.
b) Optical density is greater in the medium having less refracted angle.
c) Medium 2
Because medium 2 possess greater optical density
d) Refractive index of a medium is the ratio of the speed of light in vacuum to the speed of light in the medium.
Question 27.
Which of the following figure represents the critical angle?
Answer:
Figure (B)
Question 28.
Which phenomenon of light is made use in optical fibres that are used for communication?
Answer:
Total internal reflection
Question 29.
Choose the correct statement from the following.
(a) Total internal reflection happens when light travels from a rarer to a denser medium.
(b) Refractive index has no unit.
(c) A pencil dipped in a glass of water seems to be broken at the water-air interface due to total internal reflection.
Answer:
(b)
Question 30.
Name the devices shown below which are applications of total internal reflection.
Answer:
(a) Bicycle reflector
(b) Periscope
Question 31.
Find and write from the box what happens to the light beam in the given cases below
- Deviates towards the normal.
- Deviates away from the normal.
- No refraction occurs.
- Goes parallel to the surface of separation of the media.
- Total internal reflection occurs,
a) Light falls from water to air at an angle of 48.6°.
b) Light rays pass from air to water.
c) Light falls from water to air at an angle of 55°.
d) Light falls from water to air at an angle of incidence of 0°.
e) Light is incident from water to air at an angle of incidence of 30°.
Answer:
a) Light falls from water to air at an angle of 48.6° -Goes parallel to the surface of separation of the media.
b) Light rays pass from air to water – Deviates towards the normal.
c) Light falls from water to air at an angle of 55° Total internal reflection occurs.
d) Light falls from water to air at an angle of incidence of 0° – No refraction occurs.
e) Light is incident from water to air at an angle of incidence of 30° – Deviates away from the normal.
Question 32.
List the statements given below as Refraction, Total internal reflection, Total internal reflection and Refraction.
a) The straw is seen to be broken when placed in water.
b) The bottom of the fish tank is seen on the surface.
e) In summer, the road appears to be waler logged at a distance.
d) When the glass slab is placed over the letters, the letters appear higher.
Answer:
| Refraction | Total internal reflection | Total internal reflection and Refraction |
| a) The straw is seen to be broken when placed in water. d) When the glass slab is placed over the letters, the letters appear higher. |
b) The bottom of the fish tank is seen on the surface. | c) In summer, the road appears to be waterlogged at a distance. |
Question 33.
What are the conditions under which light does not refract when it passes through different media?
Answer:
Conditions under which light does not refract when it passes through different media
- When passing through the normal
- When light falls from a medium of higher optical density to a lower one at an angle of incidence greater than the critical angle.
- When a ray of light passes obliquely through two media having the same refractive index.
Question 34.
Correct the following statements.
a) When the refractive index increases, speed of light in the medium increases.
b) Refraction of light is utilised in optical fibre cables.
Answer:
a) When refractive index increases ,speed of Light in the medium decreases.
b) Total internal reflection is utilised in optical fibre cables.
Question 35.
Will total internal reflection occur for a ray of light entering from water to air at an angle of 49.8°? Why?
Answer:
Total internal reflection will occur for a ray of light entering from water to air at an angle of 49.8° because the angle of incidence is greater than the critical angle of water.
Question 36.
Critical angle of water with air is shown in the figure.
(a) Define critical angle.
(b) What change in the path of light will be observed if the angle of incidence is increased from critical angle?
Answer:
(a) Critical angle when a ray of light enters from an optically denser medium to a rarer medium the angle of incidence at which the angle of refraction becomes 90° is the critical angle.
(b) Yes. Increase the angle of incidence, then the ray will undergo total internal reflection, i.e., the ray will be reflected back to the same
Question 37.
A ray of light travelling from glass to air graces through the surface of glass is shown in figure.
(a) Name the angle of incidence (i) in the figure.
(b) Can we reflect back the incident ray into the glass. Justify your answer
Answer:
a) Critical angle
b) All the incident rays will be reflected back to the same medium without refraction.
Question 38.
Match the following
| Material | Critical angle |
| Water | 42° |
| Glass | 49.6° |
| 48.6° |
Answer:
| Material | Critical angle |
| Water | 48.6° |
| Glass | 42° |
Question 39.
Observe the pictures.
a) Angle of refraction in fig(1)is_(>90/90 1<90)
b) The incident angle when refracted angle is 90 is known as …………
C) Which is the phenomenon represented by these pictures?
Answer:
a) 90
b) Critical angle
c) Total internal reflection
Question 40.
Observe the figure given below.
a) Why the ray AO is reflected back to the same medium as shown above?
b) Name this phenomenon.
c) What happens to the ray of light when the angle of incidence is 40°?
Answer:
a) Light is incident at an angle which is greater than the critical angle of water.
b) Total internal reflection
c) As the angle of incidence ¡s less than critical angle, total internal reflection does not take place. Light ray gets refracted into air.
Question 41.
(a) What is the principle used in the decorative lamp shown above?
(b) Light only emerges through the tips of the libres of these decorative lamps when it trat1s through them as depicted above. What might be the reason?
Answer:
(a) Total internal reflection
(b) One end of each optical fibre in the decorative lamp is connected to a suitable source of light: Light rays from this source travel through the fibre. While travelling through the fibre, it makes an angle of incidence greater than the critical angle with the walls of the fibre. Hence the light undergoes successive total internal reflection and emerges through the other end.
Question 42.
Find and write from the pictures given as options what happens to the light ray in each of the pictures given below.
Answer:
i) Figure c)
Reason :The light ray enters from a rarer medium(air)to a denser medium (water). So the ray deviates towards the normal.
ii) Figure a)
Here the light ray enters from a denser to rarer medium,with an angle less than critical angle of glass-air medium (42°). So the ray is refracted away from the normal. Some part of the incident light is reflected back.
iii) Figure d)
The angle of incidence is greater than the critical angle of glass (42°). So the light ray undergoes total internal reflection.
Question 43.
The path of light through different media is shown in the following figure. Analyse them and answer the following questions.
a) Find out critical angle of glass.
b) Which figure represents the total internal reflection?
c) Explain how total internal reflection takes place in glass by referring the above figures.
Answer:
a) 42°
b) R
c) When a ray of light passes from a medium of higher optical density (glass) to a medium of lower optical density (air) at an angle of incidence greater than the critical angle, the ray is reflected back to the same medium without undergoing refraction. This is total internal reflection.
Question 44.
Observe the figure.
(a) AP is the path of light falling obliquely on the glass-air interface. NN’ is the normal at the point of incidence. Complete the diagram in your answer sheet to show the change in the path of the ray after P.
(b) Name the optical phenomenon that helped you to draw the path of this ray after the incidence.
(c) Write down two practical applications of this optical phenomenon.
Answer:
a) 
b) Total internal reflection
c) Practical applications
Optical fibres, Periscope, Cycle reflector