Class-10 Goyal Brothers Refraction of Light ICSE Physics Solutions Ch-5

Class-10 Goyal Brothers Refraction of Light ICSE Physics Solutions Ch-5 . We Provide Step by Step Answer of Exercise, MCQs, Numericals Practice Problem Questions of Exercise-1 Goyal Brothers Refraction ICSE Class-10 . Visit official Website CISCE  for detail information about ICSE Board Class-10 Physics.

Refraction of Light Class-10 Goyal Brothers ICSE Physics Solutions Ch-5


-: Select Topics :-

Exercise-1

 MCQ -1

Numericals Practice Problems-1

Exercise-2

 MCQ -2

Numericals Practice Problems-2

 Exercise-3


Exe-1  Class-10 Refraction of Light Goyal Brothers ICSE Physics Solutions Ch-5

Page-78,79

Question 1.
(a) What do you understand by the term refraction of light?
(b) How does the light deviate when it travels from ?

  1. a rarer to a denser medium
  2. a denser to a rarer medium?

Answer 1:
(a) Refraction of light : “When light travels from one optical medium to other optical medium, it changes its path, this change in path is called refraction of light”.
(b) (i) Towards the normal, (ii) Away from normal.

Question 2.

(a) State the laws of refraction.
(b) What do you understand by the statement that refractive index of water is 1.33 ?

Answer 2:
(a) Laws of refraction :
(i) Snell’s law : The ratio between the values of the sine of angle of incidence and the sine of angle of refraction for two given optical media is a constant quantity.
µ = sin i / sin r
(ii) The incident ray, the refracted ray and the normal lie on the same plane at the point of incidence.
(b) Refractive index of water is 1.33 means that speed of light in air is 1.33 times faster than in water.

Question 3.
Describe how will you verify the laws of refraction ?
Answer 3:
Experiment To Verify The Laws :
Fix a white sheet of paper on a drawing board. Place a rectangular glass slab in the middle of paper and draw its boundry with a pencil. The block is removed and on the boundry line KL a point O is chosen and a normal is drawn.
A New Approach to ICSE Physics Part 2 Class 10 Solutions Refraction Of Light 6
Through O a line OA at an angle i (say 60°) with the normal is drawn. The block is replaced on its boundry line. Two pins a and b are fixed vertically on the board about 10 cm apart on the line AO. Looking from the other side NM of the slab two more pins c and d are fixed such that legs of pins c and d and images of pins a and b seen through glass are in a straight line.
Pins are removed and pin pricks are marked with pencil.
Slab is removed and marks c and d are joined by line BC to meet the boundry at B. OB is joined.
AO represents INCIDENT RAY
BC represents EMERGENT RAY
OB represents REFRACTED RAY
∠ AON represents ANGLE OF INCIDENCE i
∠BOM represents ANGLE OF REFRACTION r
with O as centre and suitable radius draw a circle intersecting AO at X and OB at Y.
Draw normals XY and X’ Y’. Measure XY and X’ Y’.
A New Approach to ICSE Physics Part 2 Class 10 Solutions Refraction Of Light 7

Question 4.    Class-10 Goyal Brothers Refraction

(a) What do you understand by the term lateral displacement ?
(b) State three factors which determine lateral displacement ?

Answer 4:
(a) Lateral Displacement : “The perpendicular shift in the path of the incident ray while emerging out of an optical slab is called Lateral Displacement.”
A New Approach to ICSE Physics Part 2 Class 10 Solutions Refraction Of Light 8
(b) Factors :

  1. Angle of incidence
  2. Thickness of optical slab
  3. Refractive index of opitcal material.
  4. Wavelength of light.

Question 5.
By drawing neat diagrams explain :

(a) Why does a stick immersed obliquely in water, appear bent and short ?
(b) Why does a stamp placed under a glass block, appear raised?
(c) Why is twilight formed, before sunrise or sunset ?
(d) Why do stars twinkle, but not the planets ?
(e) Why do the faces of people sitting around a camp fire appear to shimmer ?
(f) Why does a tank filled with water and seen from above appear shallow ?
(g) Why does a fisherman aim his spear at the tail of a fish during spear fishing.
(h) Why is more than one image formed in a thick glass mirror?
(i) Why does the sun appear bigger during sunrise or sunset?

Answer 5:
(a) The stick appears to be bent and raised up in place of BA as BA’ due to refraction of light on passing from denser medium (water) to rarer medium (air)
A New Approach to ICSE Physics Part 2 Class 10 Solutions Refraction Of Light 9
(b) A stamp placed under a glass block appears raised because of refraction of light as light travels from denser to rarer medium, also due to R.I of glass observed depth is less than real depth.
(c) Twilight is formed, before the sunrise or sun set due to refraction of sun light as even when the sun is below the horizon its rays manage to reach the earth due to refraction.
(d) Stars twinkle : because of refraction of light as light passes through different layers of air of different densities mix, changes the apparent position of star. When the star is with in the line of sight it is visible but when it falls out of the line of sight, it is no longer visible. The collective effect of the above changes shift the apparent position of the star and it appears to twinkle.
Planets do not twinkle : Planets are very close to us compared to the stars. Their apparent of position also changes with change of density of different layers of the atmosphere. However the size of their apparent image is still fairly large and seldom fall out side the line of sight. Hence they do not appear to twinkle.
(e) The rays of light reflected from the face of the person, sitting opposite to you, on passing through hot air (produced by burning wood), get refracted. Since the hot air is rapidly moving and its density is continuously changing, therefore the path of the refracted rays also changes. This gives rise to the shimmering effect and person appears to shimmer.
(f) Due to refraction of light when light travels from optically denser medium (water) to optically rarer medium (air) observed depth is less than real depth, and the water tank appears to be shallow.
(g) Due to refraction of light when light travels from denser medium (water) to rarer medium (air). The real depth is more than apparent depth.
(h) In a thick glass mirror, light partially gets reflected (4%) and remaining 96% passes into the glass plate suffers refraction again and again and multiple images are formed.
(i) Sun appears to be bigger during sun set or sun rise as “The rays of light travel through maximum length of atmosphere” due to refraction, the image of sun is very much closer to the eye. Thus, it appears bigger.

Question 6.    Class-10 Goyal Brothers Refraction
What is refractive index of a material ? How is it related to (a) real and apparent depth (b) velocity of light in vacuum or air and the velocity of light in a given medium?
Answer 6:
Refractive index of a material : “Is the ratio of speed of light in vacuum (air) to the speed of light in that material”.
A New Approach to ICSE Physics Part 2 Class 10 Solutions Refraction Of Light 10


 Multiple Choice Questions-1

Refraction of Light  Class-10 Goyal Brothers  ICSE Physics Solutions

1. When a beam of light strikes a glass slab a part of it is :
(a) reflected
(b) absorbed
(c) transmitted
(d) all of these
Answer:
(a) reflected

2. The phenomenon due to which a ray of light deviates from its path while travelling from one optical medium to another optical medium is called :
(a) dispersion
(b) refraction
(c) reflection
(d) diffraction
Answer:
(b) refraction

3. When a ray of light travelling in an optically denser medium, emerges into an optically less denser medium it :
(a) deviates towards the normal
(b) deviates away from normal
(c) does not deviate
(d) gets reflected
Answer:
(b) deviates away from normal

4. A ray of light strikes a glass slab at 90°. The angle of incidence is :
(a) 90°
(b) zero
(c) less than 90°, but not zero
(d) none of these
Answer:
(b) zero

5. Two medium ‘a’ and ‘b’ have same refractive index. A ray of light travelling from medium ‘a ’ to medium ‘b’. will suffer?
(a) refraction at the interfaces
(b) partly suffer reflection at the interfaces
(c) partly gets absorbed in medium ‘b ’
(d) both (b) and (c)
Answer:
(b) partly suffer reflection at the interfaces

6. A ray of light on entering from medium ‘a’ to medium ‘b ’ does not suffer refraction. The angle of incidence in medium ‘a ’ is :
(a) 90°
(b) zero
(c) 45°
(d) 60°
Answer:
(b) zero

7. During sun rise or sun set, the sun appears bigger because the rays of light coming from it pass through
(a) larger length of atmosphere
(b) smaller length of atmosphere
(c) the earth gets closer to sun
(d) none of these
Answer:
(a) larger length of atmosphere

8. The highest refractive index is of:
(a) glass
(b) water
(c) diamond
(d) cold air
Answer:
(d) cold air

9. During spear fishing a fisherman aims at the :
(a) tail of fish
(b) head of fish
(c) slightly ahead of the head of fish
(d) none of these
Answer:
(a) tail of fish

10. When a ray of light enters into another optical medium, its wavelength and velocity change. The material in which wavelength and velocity decrease maximum, when the ray is travelling through air is :
(a) alcohol
(b) diamond
(c) glass
(d) water
Answer:
(b) diamond

11. A thick glass slab with a silvered side forms multiple images on account of :
(a) reflection of light
(b) dispersion of light
(c) refraction of light
(d) both reflection and refraction of light
Answer:
(d) both reflection and refraction of light


Numerical Problems on Refraction of Light

Refraction of Light Class-10 Goyal Brothers  ICSE Physics Solutions

Page-79,80

Practice Problem 1

Question 1.
The velocity of light in air is 3 × 108 ms-1 and in glass is 2 × 108 ms-1 Find the refractive index of glass.
Answer:
A New Approach to ICSE Physics Part 2 Class 10 Solutions Refraction Of Light 13

Question 2.
The velocity of light in air is 3 × 108 ms-1. Calculate the velocity of light in diamond or refractive index 2.5.
Answer:
A New Approach to ICSE Physics Part 2 Class 10 Solutions Refraction Of Light 13.1
A New Approach to ICSE Physics Part 2 Class 10 Solutions Refraction Of Light 14

Practice Problem 2

Question 1.
The angle of refraction in a glass block of refractive index 1.5 is 19°. Calculate the angle of incidence.
Answer:
A New Approach to ICSE Physics Part 2 Class 10 Solutions Refraction Of Light 14.1

Question 2.
Calculate the refractive index of a material, when angle of incidence in air is 50° and angle of refraction in the material is 36°.
Answer:
A New Approach to ICSE Physics Part 2 Class 10 Solutions Refraction Of Light 14.2

Practice Problem 3

Question 1.
A coin is placed at a depth of 15 cm in a beaker containing water. The refractive index of water is 4/3, calculate height through which the image of the coin is raised.
Answer:
A New Approach to ICSE Physics Part 2 Class 10 Solutions Refraction Of Light 14.3

Question 2.
The floor of a water tank appears at a depth of 2.5 m. If the refractive index of water is 1.33, find the actual depth of water.
Answer:
A New Approach to ICSE Physics Part 2 Class 10 Solutions Refraction Of Light 15

Practice Problem 4

Question 1.
A stone placed at the bottom of a water tank appears raised by 80 cm. If the refractive index of water is 4/3, find the actual depth of water in the tank :
Answer:
A New Approach to ICSE Physics Part 2 Class 10 Solutions Refraction Of Light 15.1


Exe-2 Refraction of Light Class-10 Goyal Brothers  ICSE Physics Solutions Ch-5

Page-85,86,87

Question 1.
(a) What do you understand by the following terms.

  1. Total intenta! reflection
  2. Critical angle ?

(b) Stale two conditions for total internal reflection ?
Answer:
(a) 

(i) Total internal reflection : When ray of light travels from optically denser medium to optically rarer medium and ∠i is greater than critical angle ∠r becomes more than 90° and reflects in the same denser medium and obeys the laws of reflection. The phenomenon is called total internal reflection. Hence total internal reflection : “The phenomenon due to which, a ray of light while travelling from denser medium to rarer medium gets reflected totally intenally (i.e. in the some denser medium) at the surface of separation is called total internal reflection.” i.e. ∠A’ON = ∠B’ON
A New Approach to ICSE Physics Part 2 Class 10 Solutions Refraction Of Light 16
(ii) Critical angle : When a ray of light travels from denser to rarer medium angle of incidence for when angle of refraction is of 90°, then this angle of incidence is called critical angle” i.e. ∠AON = critical angle
∵ Angle of refraction ∠N’OB = 90°
(b) Two conditions for total internal reflection :

  1. light should travel from denser to rarer medium.
  2. Angle of incidence should be more than critical angle.

Question 2.

(a) What do you understand by the statement, “critical angle for water is 48° ?
(b) Explain, how that refractive index of material is related to the critical angle.

Answer:
(a) The statement the critical angle for water is 48° means if light in water travels at ∠i = 48° it will come out in air along the surface of water
[i.e. ∠r = 90° ] A New Approach to ICSE Physics Part 2 Class 10 Solutions Refraction Of Light 17

Question 3.
Explain the following :

(a) An empty test tube placed obliquely in water, appears to be filled with mercury.
(b) Bubbles rising up in a fish tank appear silvery.
(c) Air bubbles trapped in a glass paper weight appear silvery.
(d) A crack in window pane appear silvery.
(e) Diamonds sparkle for sometime in dark.
(f) The top surface of water contained in a beaker and held above the eye level appear silvery.

Answer:
(a) An empty test tube placed in water with its mouth up ward and out side the water surface shines like mercury when seen at certain angle greater than critical angle of water. This is due to total internal reflection of light.
A New Approach to ICSE Physics Part 2 Class 10 Solutions Refraction Of Light 17.1
(b) This is due to total internal reflection. When light rays strike the bubbles at angle greater than 48°C which is critical angle of water.
(c) This is due to total internal reflection of light. Light rays strike the glass-air interface at angle more than critical angle of glass (42°) and get totally internally reflected.
(d) A crack in a glass window pane appear silvery on account of the presence of air in the crack due to total internal reflection.
(e) Diamond is cut in such a way that a number of refracting surfaces are present and total internal reflection takes place at a number of places and critical angle of diamond beings 24° cuts at very sharp angles are made so that the ray gets trapped with in the diamond for some time.
(f) When light gets totally internally reflected at water air interface, it appears silvery.

Question 4.

(a) What is a totally reflecting prism ?
(b) By drawing neat diagram explain how totally reflecting prisms are used to turn (i) rays through 90° (ii) rays through 180°.
(c) How is a totally reflecting prism used as an erecting prism ?

Answer:
(a) Totally reflecting prism : “A prism having on angle of 90° between its two refraction surfaces and the other two angles each equal to 45° is called total reflecting prism because the light incident normally on any of its faces, suffers total internal reflection inside the prims.”
(b)

  1. To turn rays through 90°
    A New Approach to ICSE Physics Part 2 Class 10 Solutions Refraction Of Light 18
  2. To turn rays through 180°
    A New Approach to ICSE Physics Part 2 Class 10 Solutions Refraction Of Light 19

(c) Totally reflecting prism as erecting prism :
A New Approach to ICSE Physics Part 2 Class 10 Solutions Refraction Of Light 19.1

Light rays from object PQ suffer refraction air to glass and strike the face AC of prism from glass to air at angle greater than critical angle (42°) and suffers total internal reflection. Then strikes face BC at angle less than critical angle and suffers refraction from glass to air and bends a way from normal and beam emerges parallel to face AC. Erect image P’Q’ is obtained and prism acts as erecting prism.

Question 5.
(a) Trace the course of rays through an equilateral glass prism, showing clearly

  1. angle of incidence
  2. angle of refraction
  3. angle of the prism
  4. angle of deviation
  5. angle of emergence.

(b) On what factors do the angle of deviation in a prism depend?
(c) What do you understand by the term angle of minimum deviation ? In this position how is the angle of incidence related to the angle of emergence ?
Answer:
(a) The course of rays through equilateral glass prism :

  1. ∠OPN – angle of incidence
  2. Angle of refraction ∠NPQ is angle of refraction
    A New Approach to ICSE Physics Part 2 Class 10 Solutions Refraction Of Light 20
  3. ∠BAC is angle of prism.
  4. Angle of deviation ∠LMR
  5. Angle of emergence e

(b) Factors effecting the angle of deviation :

  1. The angle of incidence i
  2. Angle of prism (A)
  3. Colour of wavelength (λ) of light used.
  4. R.I. of prism (material of prism).

(c) Angle of minimum deviation : The angle between incident ray produced and emergent ray produced is called angle of deviation. The angle of deviation decreases with increase in angle of incidence. A stage comes when for a particular value of angle of incidence, the angle of deviation is minimum.
If the angle of incidence is further increased, the angle, of deviation starts increasing. Hence
Angle of minimum deviation is the angle of incidence for which angle of deviation is minimum.

Question 6.
State four differences between reflection and total internal reflection.
Answer:
Total Internal Reflection :

  1. The entire light is reflected.
  2. There is no loss of energy.
  3. It takes place only when light passes from denser to rarer medium at an angle of incidence is greater than critical angle.
  4. The image is much brighter.

Reflection :

  1. Only a part of light is reflected Rest is refracted and absorbed.
  2. The energy of reflected ray is less than incident ray.
  3. It takes place when light is incident on plane mirror from any medium at any angle of incidence.
  4. The image is less bright.

Multiple Choice Questions-2

Refraction of Light Class-10 Goyal Brothers  ICSE Physics Solutions

1. For total internal reflection to take place a ray of light must :
(a) travel from denser to rarer medium
(b) travel from rarer to denser medium
(c) medium does not play any role
(d) none of these
Answer:
(a) travel from denser to rarer medium

2. The critical angle for glass is 42°. The corresponding angle of refraction is :
(a) 0°
(b) 90°
(c) lesser than 90° but more than 42°
(d) no angle of refraction.
Answer:
(b) 90°

3. The critical angle for a material X is 45°. The total internal reflection will take place, if the angle of incidence in the denser medium is :
(a) less than 45°
(b) 90°
(c) more than 45°, but not 90°
(d) less than 45°, but not zero degree
Answer:
(c) more than 45°, but not 90°

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