Solutions of Refraction of Light (Page No- 227 & 228) - Physics By Lakhmir Singh, Class 10 Class 10 Notes | EduRev

Class 10 Physics Solutions By Lakhmir Singh & Manjit Kaur

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Class 10 : Solutions of Refraction of Light (Page No- 227 & 228) - Physics By Lakhmir Singh, Class 10 Class 10 Notes | EduRev

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Lakhmir Singh Physics Class 10 Solutions Page No:227

Question 1: What name is given to the ratio of sine of angle of incidence to the sine of angle of refraction ?

Solution : Refractive index.

Question 2: Write the relation between the angle of incidence and the angle of refraction for a medium.

Solution : Refractive index = sine of the angle of incidence/sine of the angle of refraction.


Lakhmir Singh Physics Class 10 Solutions Page No:228

Question 3: What is the unit of refractive index ?

Solution : Refractive index has no units.

Question 4: Which has higher refractive index : water or glass ?

Solution : Glass has higher refractive index.

Question 5: Refractive indices of carbon disulphide and ethyl alcohol are 1.63 and 1.36 respectively. Which is optically denser ?

Solution : Carbon disulphide is more denser than the ethyl alcohol.

Question 6: The refractive index of diamond is 2.42. What is the meaning of this statement in relation to the speed of light ?

Solution : This means that the ratio of the speed of light in air to the speed of light in diamond is equal to 2.42.

Question 7: If the refractive index for light going from air to diamond be 2.42, what will be the refractive index for light going from diamond to air ?

Solution :

Solutions of Refraction of Light (Page No- 227 & 228) - Physics By Lakhmir Singh, Class 10 Class 10 Notes | EduRev

Question 8: How is the refractive index of a material related to the speed of light in it ?

Solution : Refractive index of a material  Solutions of Refraction of Light (Page No- 227 & 228) - Physics By Lakhmir Singh, Class 10 Class 10 Notes | EduRev

Question 9: Fill in the following blank with a suitable word :
 When a ray of light goes from air into a clear material, you see the ray bend. How much the ray bends is determined by the………………………. of the material.

Solution : Refractive index.

Question 10: Give three examples of materials that refract light rays. What happens to the speed of light rays when they enter these materials ?

Solution : Three examples of materials that refract light rays are water, glass and diamond. When light rays (travelling in air) enter these materials, their speed decreases.

Question 11: Define Snell’s law of refraction. A ray of light is incident on a glass slab at an angle of incidence of 60°. If the angle of refraction be 32.7°, calculate the refractive index of glass. (Given : sin 60° = 0.866, and sin 32.7° = 540).

Solution : Snell's law: According to the Snell's law of refraction, the ratio of sine of angle of incidence to the sine of angle of refraction is constant for a given pair of media. 

Solutions of Refraction of Light (Page No- 227 & 228) - Physics By Lakhmir Singh, Class 10 Class 10 Notes | EduRev

Given: Angle of incidence = 60°
Angle of refraction = 32.4° 

Solutions of Refraction of Light (Page No- 227 & 228) - Physics By Lakhmir Singh, Class 10 Class 10 Notes | EduRev

Solutions of Refraction of Light (Page No- 227 & 228) - Physics By Lakhmir Singh, Class 10 Class 10 Notes | EduRev

Question 12: The speed of light in vacuum and in two different glasses is given in the table below :

Medium
Speed of light
Vaccume
Flint glass
crown glass
3.00 x 10m/s
1.86 x 108 m/s
1.97 x 108 m/s


(a) Calculate the absolute refractive indexes of flint glass and crown glass.
 (b) Calculate the relative refractive index for light going from crown glass to flint glass.

Solution :

Solutions of Refraction of Light (Page No- 227 & 228) - Physics By Lakhmir Singh, Class 10 Class 10 Notes | EduRev
Solutions of Refraction of Light (Page No- 227 & 228) - Physics By Lakhmir Singh, Class 10 Class 10 Notes | EduRev

Question 13: The speed of light in air is 3 × 108 m/s. In medium X its speed is 2 × 108 m/s and in medium Y the speed of light is 2.5 × 108 m/s. Calculate:
 (a) air nx (b) air ny (c) xny

Solution :

Given: Speed of light in air = 3.0x108m/s
Speed of light in medium X = 2.0x108m/s
Speed of light in medium Y = 2.50x108m/s

(a) airnx = ? 

Solutions of Refraction of Light (Page No- 227 & 228) - Physics By Lakhmir Singh, Class 10 Class 10 Notes | EduRev
Solutions of Refraction of Light (Page No- 227 & 228) - Physics By Lakhmir Singh, Class 10 Class 10 Notes | EduRev
Solutions of Refraction of Light (Page No- 227 & 228) - Physics By Lakhmir Singh, Class 10 Class 10 Notes | EduRev

Question 14: What is the speed of light in a medium of refractive index 6/5 if its speed in air is 3,00,000 km/s ?

Solution : Refractive index of medium = 6/5 = 1.2
Speed of light in air = 3,00.000km/s

We know that 

Solutions of Refraction of Light (Page No- 227 & 228) - Physics By Lakhmir Singh, Class 10 Class 10 Notes | EduRev
Solutions of Refraction of Light (Page No- 227 & 228) - Physics By Lakhmir Singh, Class 10 Class 10 Notes | EduRev

Question 15: The refractive index of glass is 1.5. Calculate the speed of light in glass. The speed of light in air is 3.0 × 108ms-1.

Solution : Given:-Refractive index of glass = 1.5
Speed of light in air = 3.0x108m/s

We know that 

Solutions of Refraction of Light (Page No- 227 & 228) - Physics By Lakhmir Singh, Class 10 Class 10 Notes | EduRev

Question 16: The speed of light in water is 2.25 × 108 m/s. If the speed of light in vacuum be 3 × 108 m/s, calculate the refractive index of water.

Solution :  Speed of light in vacuum = 3.0x108m/s
Speed of light in water = 2.25 x108m/s 
Refractive index of water = ?

We know that 

Solutions of Refraction of Light (Page No- 227 & 228) - Physics By Lakhmir Singh, Class 10 Class 10 Notes | EduRev

Question 17: Light enters from air into diamond which has a refractive index of 2.42. Calculate the speed of light in diamond. The speed of light in air is 3.0 × 108 ms-1.

Solution : Given:- Refractive index of diamond = 2.42
Speed of light in air = 3.0x108m/s We know that

Solutions of Refraction of Light (Page No- 227 & 228) - Physics By Lakhmir Singh, Class 10 Class 10 Notes | EduRev

Question 18: (a) State and explain the laws of refraction of light with the help of a labelled diagram.
 (b) What is meant by the refractive index of a substance ?
 (c) Light travels through air at 300 million ms-1. On entering water it slows down to 225 million ms-1

Calculate the refractive index of water.

Solution : 

(a) Law of refraction

Solutions of Refraction of Light (Page No- 227 & 228) - Physics By Lakhmir Singh, Class 10 Class 10 Notes | EduRev

First law: According to the first law of refraction, the incident ray. the refracted ray and the normal at the point of incidence, all lie in the same plane. 

Second law: According to the second law of refraction, the ratio of the sine of angle of Incidence to the sine of angle of refraction is constant for a given pair of media. 

(b) Refractive index of substance: The ratio of speed of light In vacuum to the speed of light In a medium. Is called the refractive index of that medium. 

(c) Speed of light in air = 300 milion m/sec

Speed of light in water = 225 milion m/sec

We know that 

Solutions of Refraction of Light (Page No- 227 & 228) - Physics By Lakhmir Singh, Class 10 Class 10 Notes | EduRev

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