Selina Textbook Solutions: Refraction of Light at Plane Surfaces | Physics Class 10 ICSE PDF Download

 Page 1


Class X            Chapter – 04 Refraction of Light at Plane Surface         Physics 
_____________________________________________________________________________ 
                      
 
EXERCISE - 4 (A) 
 
Question 1: 
What do you understand by refraction of light? 
Solution 1: 
The change in the direction of the path of light, when it passes from one transparent medium to 
another transparent medium, is called refraction of light. 
 
 
Question 2: 
Draw diagrams to show the refraction of light from (i) air to glass, (ii) glass to air. In each 
diagram, label the incident ray, refracted ray, the angle of incidence (i) and the angle of refraction 
(r).  
Solution 2: 
Diagram showing the refraction of light from Air to glass 
 
 
 
Diagram showing the refraction of light from Glass to Air 
 
  
 
 
 
Page 2


Class X            Chapter – 04 Refraction of Light at Plane Surface         Physics 
_____________________________________________________________________________ 
                      
 
EXERCISE - 4 (A) 
 
Question 1: 
What do you understand by refraction of light? 
Solution 1: 
The change in the direction of the path of light, when it passes from one transparent medium to 
another transparent medium, is called refraction of light. 
 
 
Question 2: 
Draw diagrams to show the refraction of light from (i) air to glass, (ii) glass to air. In each 
diagram, label the incident ray, refracted ray, the angle of incidence (i) and the angle of refraction 
(r).  
Solution 2: 
Diagram showing the refraction of light from Air to glass 
 
 
 
Diagram showing the refraction of light from Glass to Air 
 
  
 
 
 
Class X            Chapter – 04 Refraction of Light at Plane Surface         Physics 
_____________________________________________________________________________ 
 
Question 3: 
A ray of light is incident normally on a plane glass slab. What will be (i) the angle of refraction 
and (ii) the angle of deviation for the ray? 
Solution 3: 
The ray of light which is incident normally on a plane glass slab passes undeviated. That is such 
a ray suffers no bending at the surface because here the angle of incidence is 0°. Thus if angle 
of incidence ?i= 0°, then the angle of refraction ?r = 0°. And the angle of deviation of the ray 
will also be 0°.  
 
 
Question 4: 
What is the cause of refraction of light when it passes from one medium to another? 
Solution 4: 
The refraction of light (or change in the direction of path of light in other medium) occurs 
because light travels with different speeds in different media. When a ray of light passes from 
one medium to another, its direction (except for ?i = 0°) changes because of change in its speed.  
 
 
Question 5: 
A light ray suffers reflection and refraction at the boundary in passing from air to water. Draw 
a neat labelled ray diagram to show it. 
Solution 5: 
Air is a rarer medium while water is denser than air with refractive index of 1.33. Therefore 
when light ray will travel from air to water it will bend towards the normal. 
 
  
 
 
Question 6: 
A ray of light passes from medium 1 to medium 2. Which of the following quantities of the 
refracted ray will differ from that of the incident ray: Speed, intensity, frequency, wavelength? 
Solution 6: 
Speed, intensity and wavelength  
 
Page 3


Class X            Chapter – 04 Refraction of Light at Plane Surface         Physics 
_____________________________________________________________________________ 
                      
 
EXERCISE - 4 (A) 
 
Question 1: 
What do you understand by refraction of light? 
Solution 1: 
The change in the direction of the path of light, when it passes from one transparent medium to 
another transparent medium, is called refraction of light. 
 
 
Question 2: 
Draw diagrams to show the refraction of light from (i) air to glass, (ii) glass to air. In each 
diagram, label the incident ray, refracted ray, the angle of incidence (i) and the angle of refraction 
(r).  
Solution 2: 
Diagram showing the refraction of light from Air to glass 
 
 
 
Diagram showing the refraction of light from Glass to Air 
 
  
 
 
 
Class X            Chapter – 04 Refraction of Light at Plane Surface         Physics 
_____________________________________________________________________________ 
 
Question 3: 
A ray of light is incident normally on a plane glass slab. What will be (i) the angle of refraction 
and (ii) the angle of deviation for the ray? 
Solution 3: 
The ray of light which is incident normally on a plane glass slab passes undeviated. That is such 
a ray suffers no bending at the surface because here the angle of incidence is 0°. Thus if angle 
of incidence ?i= 0°, then the angle of refraction ?r = 0°. And the angle of deviation of the ray 
will also be 0°.  
 
 
Question 4: 
What is the cause of refraction of light when it passes from one medium to another? 
Solution 4: 
The refraction of light (or change in the direction of path of light in other medium) occurs 
because light travels with different speeds in different media. When a ray of light passes from 
one medium to another, its direction (except for ?i = 0°) changes because of change in its speed.  
 
 
Question 5: 
A light ray suffers reflection and refraction at the boundary in passing from air to water. Draw 
a neat labelled ray diagram to show it. 
Solution 5: 
Air is a rarer medium while water is denser than air with refractive index of 1.33. Therefore 
when light ray will travel from air to water it will bend towards the normal. 
 
  
 
 
Question 6: 
A ray of light passes from medium 1 to medium 2. Which of the following quantities of the 
refracted ray will differ from that of the incident ray: Speed, intensity, frequency, wavelength? 
Solution 6: 
Speed, intensity and wavelength  
 
Class X            Chapter – 04 Refraction of Light at Plane Surface         Physics 
_____________________________________________________________________________ 
 
 
Question 7: 
State the snell’s laws of refraction of light. 
Solution 7: 
The Snell's laws of refraction are: 
1. The incident ray, the refracted ray and the normal at the point of incidence, all lie in the 
same plane. 
2. The ratio of the sine of the angle of incidence to the sine of the angle of refraction is constant 
for the pair of the given media. 
???????? ???????? = 1
µ
2 
 
where 1
µ
2 is known as the refractive index of the second medium with respect to the first medium.  
 
 
Question 8: 
Define the term refraction index of a medium. Can it be less than 1? 
Solution 8: 
The refractive index of second medium with respect to first medium is defined as the ratio of the 
sine of angle of incidence in the first medium to the sine of the angle of refraction in the second 
medium. 
  
Refractive index of a medium is always greater than 1 (it cannot be less than 1) because the 
speed of light in any medium is always less than that in vacuum.  
 
 
Question 9: 
How is the refractive index of a medium related to the speed of light in it? 
Solution 9: 
Denser medium has a higher refractive index and therefore the speed of light in such medium is 
lower in comparison to the speed of light in a medium which has a lower refractive index.  
 
 
Question 10: 
A light ray passes from to (a) air, (b) glass. In each case state, how does the speed of light change. 
Solution 10: 
(a) Air (its refractive index is less than that of water) 
(b) Glass (its refractive index is more than that of water)  
 
 
Question 11: 
A light ray in passing from water to a medium (a) speeds up (b) slows down. In each case, give 
one example of the medium. 
Page 4


Class X            Chapter – 04 Refraction of Light at Plane Surface         Physics 
_____________________________________________________________________________ 
                      
 
EXERCISE - 4 (A) 
 
Question 1: 
What do you understand by refraction of light? 
Solution 1: 
The change in the direction of the path of light, when it passes from one transparent medium to 
another transparent medium, is called refraction of light. 
 
 
Question 2: 
Draw diagrams to show the refraction of light from (i) air to glass, (ii) glass to air. In each 
diagram, label the incident ray, refracted ray, the angle of incidence (i) and the angle of refraction 
(r).  
Solution 2: 
Diagram showing the refraction of light from Air to glass 
 
 
 
Diagram showing the refraction of light from Glass to Air 
 
  
 
 
 
Class X            Chapter – 04 Refraction of Light at Plane Surface         Physics 
_____________________________________________________________________________ 
 
Question 3: 
A ray of light is incident normally on a plane glass slab. What will be (i) the angle of refraction 
and (ii) the angle of deviation for the ray? 
Solution 3: 
The ray of light which is incident normally on a plane glass slab passes undeviated. That is such 
a ray suffers no bending at the surface because here the angle of incidence is 0°. Thus if angle 
of incidence ?i= 0°, then the angle of refraction ?r = 0°. And the angle of deviation of the ray 
will also be 0°.  
 
 
Question 4: 
What is the cause of refraction of light when it passes from one medium to another? 
Solution 4: 
The refraction of light (or change in the direction of path of light in other medium) occurs 
because light travels with different speeds in different media. When a ray of light passes from 
one medium to another, its direction (except for ?i = 0°) changes because of change in its speed.  
 
 
Question 5: 
A light ray suffers reflection and refraction at the boundary in passing from air to water. Draw 
a neat labelled ray diagram to show it. 
Solution 5: 
Air is a rarer medium while water is denser than air with refractive index of 1.33. Therefore 
when light ray will travel from air to water it will bend towards the normal. 
 
  
 
 
Question 6: 
A ray of light passes from medium 1 to medium 2. Which of the following quantities of the 
refracted ray will differ from that of the incident ray: Speed, intensity, frequency, wavelength? 
Solution 6: 
Speed, intensity and wavelength  
 
Class X            Chapter – 04 Refraction of Light at Plane Surface         Physics 
_____________________________________________________________________________ 
 
 
Question 7: 
State the snell’s laws of refraction of light. 
Solution 7: 
The Snell's laws of refraction are: 
1. The incident ray, the refracted ray and the normal at the point of incidence, all lie in the 
same plane. 
2. The ratio of the sine of the angle of incidence to the sine of the angle of refraction is constant 
for the pair of the given media. 
???????? ???????? = 1
µ
2 
 
where 1
µ
2 is known as the refractive index of the second medium with respect to the first medium.  
 
 
Question 8: 
Define the term refraction index of a medium. Can it be less than 1? 
Solution 8: 
The refractive index of second medium with respect to first medium is defined as the ratio of the 
sine of angle of incidence in the first medium to the sine of the angle of refraction in the second 
medium. 
  
Refractive index of a medium is always greater than 1 (it cannot be less than 1) because the 
speed of light in any medium is always less than that in vacuum.  
 
 
Question 9: 
How is the refractive index of a medium related to the speed of light in it? 
Solution 9: 
Denser medium has a higher refractive index and therefore the speed of light in such medium is 
lower in comparison to the speed of light in a medium which has a lower refractive index.  
 
 
Question 10: 
A light ray passes from to (a) air, (b) glass. In each case state, how does the speed of light change. 
Solution 10: 
(a) Air (its refractive index is less than that of water) 
(b) Glass (its refractive index is more than that of water)  
 
 
Question 11: 
A light ray in passing from water to a medium (a) speeds up (b) slows down. In each case, give 
one example of the medium. 
Class X            Chapter – 04 Refraction of Light at Plane Surface         Physics 
_____________________________________________________________________________ 
 
Solution 11: 
In case (i) the refractive index of the medium 2 is less than the refractive index of medium 1 
because the ray of light speeds up. 
While in case (ii) the refractive index of the medium 2 is greater than the refractive index of 
medium 1 due to because here the ray of light slows down.  
 
 
Question 12: 
How does the speed of light change when it passes from glass to water? 
Solution 12: 
Refractive index of water, µ w = 1.33 
Refractive index of air, µ a = 1.0003 
Refractive index of glass, µ g = 1.5 
This implies that µ a <  µ w  < µ g 
The speed of light decreases when it enters from a rarer medium to denser medium and increases 
when it enters from a denser medium to rarer medium. 
Therefore, the speed of light increases when light ray passes from water to air and the speed of 
light decreases when light ray passes from water to glass. 
 
 
Question 13: 
A ray of light is passing from a transparent medium 1 to another transparent medium 2 (i) 
Speed up (ii) slows down. In each case, state whether the refractive index of medium 2 is 
equal to, less than or greater than the refractive index of medium 1. 
Solution 13: 
In case (i) the refractive index of the medium 2 is less than the refractive index of medium 1 
because the ray of light speeds up. 
While in case (ii) the refractive index of the medium 2 is greater than the refractive index of 
medium 1 due to because here the ray of light slows down. 
 
 
Question 14: 
What do you understand by the statement the refractive index of glass is 1.5 for white light? 
Solution 14: 
The refractive index of glass is 1.5 for white light means white light travels in air 1.5 times faster 
than in glass. 
 
 
Question 15: 
A monochromatic ray of light passes from air to glass. The wavelength of light in air is ?, the 
speed of light in air is c and in glass is ?. If the absolute refractive index of glass is 1.5, write 
down (a) the relationship between ?? and ?, (b) the wavelength of light in glass. 
 
Page 5


Class X            Chapter – 04 Refraction of Light at Plane Surface         Physics 
_____________________________________________________________________________ 
                      
 
EXERCISE - 4 (A) 
 
Question 1: 
What do you understand by refraction of light? 
Solution 1: 
The change in the direction of the path of light, when it passes from one transparent medium to 
another transparent medium, is called refraction of light. 
 
 
Question 2: 
Draw diagrams to show the refraction of light from (i) air to glass, (ii) glass to air. In each 
diagram, label the incident ray, refracted ray, the angle of incidence (i) and the angle of refraction 
(r).  
Solution 2: 
Diagram showing the refraction of light from Air to glass 
 
 
 
Diagram showing the refraction of light from Glass to Air 
 
  
 
 
 
Class X            Chapter – 04 Refraction of Light at Plane Surface         Physics 
_____________________________________________________________________________ 
 
Question 3: 
A ray of light is incident normally on a plane glass slab. What will be (i) the angle of refraction 
and (ii) the angle of deviation for the ray? 
Solution 3: 
The ray of light which is incident normally on a plane glass slab passes undeviated. That is such 
a ray suffers no bending at the surface because here the angle of incidence is 0°. Thus if angle 
of incidence ?i= 0°, then the angle of refraction ?r = 0°. And the angle of deviation of the ray 
will also be 0°.  
 
 
Question 4: 
What is the cause of refraction of light when it passes from one medium to another? 
Solution 4: 
The refraction of light (or change in the direction of path of light in other medium) occurs 
because light travels with different speeds in different media. When a ray of light passes from 
one medium to another, its direction (except for ?i = 0°) changes because of change in its speed.  
 
 
Question 5: 
A light ray suffers reflection and refraction at the boundary in passing from air to water. Draw 
a neat labelled ray diagram to show it. 
Solution 5: 
Air is a rarer medium while water is denser than air with refractive index of 1.33. Therefore 
when light ray will travel from air to water it will bend towards the normal. 
 
  
 
 
Question 6: 
A ray of light passes from medium 1 to medium 2. Which of the following quantities of the 
refracted ray will differ from that of the incident ray: Speed, intensity, frequency, wavelength? 
Solution 6: 
Speed, intensity and wavelength  
 
Class X            Chapter – 04 Refraction of Light at Plane Surface         Physics 
_____________________________________________________________________________ 
 
 
Question 7: 
State the snell’s laws of refraction of light. 
Solution 7: 
The Snell's laws of refraction are: 
1. The incident ray, the refracted ray and the normal at the point of incidence, all lie in the 
same plane. 
2. The ratio of the sine of the angle of incidence to the sine of the angle of refraction is constant 
for the pair of the given media. 
???????? ???????? = 1
µ
2 
 
where 1
µ
2 is known as the refractive index of the second medium with respect to the first medium.  
 
 
Question 8: 
Define the term refraction index of a medium. Can it be less than 1? 
Solution 8: 
The refractive index of second medium with respect to first medium is defined as the ratio of the 
sine of angle of incidence in the first medium to the sine of the angle of refraction in the second 
medium. 
  
Refractive index of a medium is always greater than 1 (it cannot be less than 1) because the 
speed of light in any medium is always less than that in vacuum.  
 
 
Question 9: 
How is the refractive index of a medium related to the speed of light in it? 
Solution 9: 
Denser medium has a higher refractive index and therefore the speed of light in such medium is 
lower in comparison to the speed of light in a medium which has a lower refractive index.  
 
 
Question 10: 
A light ray passes from to (a) air, (b) glass. In each case state, how does the speed of light change. 
Solution 10: 
(a) Air (its refractive index is less than that of water) 
(b) Glass (its refractive index is more than that of water)  
 
 
Question 11: 
A light ray in passing from water to a medium (a) speeds up (b) slows down. In each case, give 
one example of the medium. 
Class X            Chapter – 04 Refraction of Light at Plane Surface         Physics 
_____________________________________________________________________________ 
 
Solution 11: 
In case (i) the refractive index of the medium 2 is less than the refractive index of medium 1 
because the ray of light speeds up. 
While in case (ii) the refractive index of the medium 2 is greater than the refractive index of 
medium 1 due to because here the ray of light slows down.  
 
 
Question 12: 
How does the speed of light change when it passes from glass to water? 
Solution 12: 
Refractive index of water, µ w = 1.33 
Refractive index of air, µ a = 1.0003 
Refractive index of glass, µ g = 1.5 
This implies that µ a <  µ w  < µ g 
The speed of light decreases when it enters from a rarer medium to denser medium and increases 
when it enters from a denser medium to rarer medium. 
Therefore, the speed of light increases when light ray passes from water to air and the speed of 
light decreases when light ray passes from water to glass. 
 
 
Question 13: 
A ray of light is passing from a transparent medium 1 to another transparent medium 2 (i) 
Speed up (ii) slows down. In each case, state whether the refractive index of medium 2 is 
equal to, less than or greater than the refractive index of medium 1. 
Solution 13: 
In case (i) the refractive index of the medium 2 is less than the refractive index of medium 1 
because the ray of light speeds up. 
While in case (ii) the refractive index of the medium 2 is greater than the refractive index of 
medium 1 due to because here the ray of light slows down. 
 
 
Question 14: 
What do you understand by the statement the refractive index of glass is 1.5 for white light? 
Solution 14: 
The refractive index of glass is 1.5 for white light means white light travels in air 1.5 times faster 
than in glass. 
 
 
Question 15: 
A monochromatic ray of light passes from air to glass. The wavelength of light in air is ?, the 
speed of light in air is c and in glass is ?. If the absolute refractive index of glass is 1.5, write 
down (a) the relationship between ?? and ?, (b) the wavelength of light in glass. 
 
Class X            Chapter – 04 Refraction of Light at Plane Surface         Physics 
_____________________________________________________________________________ 
 
Solution 15: 
(a) The relation between speed of light in air c and in glass v is given by 
 
 
?? ?? = ?? ???? ?? = 1.5 ?? 
 
(b) The wavelength of light in glass (? 
1
)  
 
     µ = 
?? ?? 1
 = 
?? 1.5
  
 
 
Question 16: 
For which colour of white light, is the refractive index of a transparent medium (a) the least (b) 
the most? 
Solution 16: 
(a) The least for red colour and (b) the most for violet colour.  
 
 
Question 17: 
Name two factors on which the refractive index of a medium depends? State how does it depend 
on the factors stated by you. 
Solution 17: 
The two factors on which the refractive index of a medium depends are: 
1) Nature of a medium i.e. its optical density (e.g. µ g = 1.5, µ w = 1.33) - Smaller the speed of 
light in a medium relative to air, higher is the refractive index of that medium.  
2) Physical condition such as temperature - with increase in temperature, the speed of light in 
medium increases, so the refractive index of medium decreases. 
 
 
Question 18: 
How does the refractive index of a medium depend on the wavelength of light used? 
Solution 18: 
Refractive index of a medium decreases with increase in wavelength of light. 
Refractive index of a medium for violet light (least wavelength) is greater than that for red light 
(greatest wavelength).  
 
 
Question 19: 
How does the refractive index of a medium depend on its temperature?  
Solution 19: 
Refractive index of a medium decreases with the increase in temperature.