# 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?

(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 ?

(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 ?
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.

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’.

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 ?

(a) Lateral Displacement : “The perpendicular shift in the path of the incident ray while emerging out of an optical slab is called Lateral Displacement.”

(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?

(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)

(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?
Refractive index of a material : “Is the ratio of speed of light in vacuum (air) to the speed of light in that material”.

### 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
(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
(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
(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
(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)
(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°
(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
(a) larger length of atmosphere

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

9. During spear fishing a fisherman aims at the :
(a) tail of fish
(d) none of these
(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
(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
(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.

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.

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.

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°.

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.

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.

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 :

### 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 ?
(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

(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.

(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° ]

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.

(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.

(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 ?

(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°
2. To turn rays through 180°

(c) Totally reflecting prism as erecting prism :

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 ?
(a) The course of rays through equilateral glass prism :

1. ∠OPN – angle of incidence
2. Angle of refraction ∠NPQ is angle of refraction
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.
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
(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.
(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
(c) more than 45°, but not 90°

4. Diamonds sparkle more than the glass, because they have :
(a) smaller critical angle than the glass
(b) larger critical angle than the glass
(c) critical angle plays no role
(d) none of these
(c) critical angle plays no role

5. Small air bubbles rising up a fish tank appear silvery when viewed from some particular angle because of the phenomenon of :
(a) reflection
(b) refraction
(c) total internal reflection
(d) dispersion
(c) total internal reflection

6. An isosceles totally reflecting prism can reflect rays through an angle of :
(a) 60°
(b) 90°
(c) 180°
(d) both (b) and (c)
(d) both (b) and (c)

7. A ray of light is incident on the face of an equilateral prism at angle of 90°. The ray gets totally reflected on the second refracting face. The total deviation produced in the path of ray is :
(a) 60°
(b) 90°
(c) 120°
(d) 180°
(c) 120°

8. A crack in the window pane appears silvery when viewed from some particular angle. This phenomenon due to :
(a) refelction light
(b) refraction of light
(c) total internal reflection of light
(d) dispersion of light
(c) total internal reflection of light

9. When an equilateral prism is in minimum deviation position the angle of incidence is :
(a) greater than the angle of emergence
(b) smaller than the angle of emergence
(c) equal to the angle of emergence
(d) none of these
(c) equal to the angle of emergence

10. A prism has :
(a) two rectangular and three triangular surfaces
(b) two triangular and three rectangular surfaces
(c) three rectangular and three triangular surfaces
(d) none of these
(b) two triangular and three rectangular surfaces

11. When a ray of light passes through an equilateral glass prism :
(a) it suffers refraction on the first refracting surfaces
(b) it suffers refraction on both the refracting surfaces
(c) it bends towards the base on both refracting surfaces
(d) both (b) and (c)
(d) both (b) and (c)

### Numerical Problems on Lenses -2

Refraction of Light  Class-10 Goyal Brothers  ICSE Physics Solutions

Page-96,97,98,99

Practice Problems 1

Question 1.
A convex lens of focal length 10 cm is placed at a distance of 60 cm from a screen. How far from the lens should be placed an object so as to obtain a real image on the screen? Calculate the magnification of the image and its characteristics.

Question 2.
An object of height 3 cm is placed at a distance of 24 cm from a convex lens of focal length 10 cm, when an image is formed on the screen on the other side of the lens. Calculate

(a) the distance of the screen from the lens
(b) the size of image
(c) the characteristics of image.

Practice Problems 2

Question 1.
An object when placed in front of a convex lens forms a real image of 0.5 magnification. If the distance of the image from the lens is 24 cm, calculate focal length of the lens.

Question 2.
A convex lens forms a real image 4 times magnified when placed at a distance of 6 cm from the lens. Calculate the focal length of the lens.

Practice Problems 3

Question 1.
An object 1.4 cm high when placed in front of a convex lens at a distance of 6 cm, forms a virtual image at a distance of 24 cm from the lens. Calculate

(a) the focal length of the lens
(b) the size of the image.

Question 2.
A convex lens forms a 2.5 times magnified virtual image when an object is placed at a distance of 8 cm from the lens. Calculate

(a) the distance of the image from the lens
(b) the focal length of lens.

Question 3.
An object 1 cm high is placed at a distance of 4 cm from a convex lens of focal length 6 cm. Calculate

(a) the position of the image
(b) size of a image. State the characteristics of the image.

Practice Problems 4

Question 1.      Class-10 Goyal Brothers Refraction
An object 2 cm high is placed at a distance of 25 cm from the optical centre of a concave lens offocal length 15 cm. Calculate

(a) the position of the image
(b) the size of the image.

Question 2.
A concave lens forms 4 times diminished and virtual image when an object is placed at a distance of 80 cm. Calculate

(a) the position of the image
(b) the focal length of the lens.

Question 3.
A concave lens has focal length 15 cm. At what distance should the object from the lens be placed, so as to form an image at 10 cm from the lens. Also find magnification of the lens.

Practice Problems 5

Question 1.      Class-10 Goyal Brothers Refraction
A converging lens has a focal length 40 cm. Calculate its power.

Question 2.
A lens which forms a real image has a focal length 8 cm. Calculate its power.

Practice Problems 6

Question 1.
State the nature of the lens and the focal length if its power is +4D.

Question 2.
The number of the glasses of a person is +0.75 D. What is the nature of the lens and what is its focal length ?

Practice Problems 7

Question 1.
The focal length of a concave lens is 10 cm. Calculate its power.

Question 2.
The focal length of the lens of a myopic person is 40 cm. What is the power of the lens ?

Practice Problems 8

Question 1.
Calculate the focal length of a lens of power -2.75 D.

Question 2.
The power of a concave lens is -12.5 D. What is the focal length of the lens ?

### Exe-3  Refraction of Light  Class-10 Goyal Brothers  ICSE Physics Solutions Ch-5

Page-99,100

Question 1.

(a) What do you understand by the term lens ?
(b) What ar the various kinds of lenses ? Draw a neat diagram of each kind.

(a) Lens : “Is a piece of transparent optical medium material having one or two spherical surfaces.”
Or
“A lens is a transparent refracting medium bounded by two curved surfaces which art generally spherical.”
(b) There are two types of lenses :

Question 2.    Class-10 Goyal Brothers Refraction
Define the following with respect to converging lens

1. principal axis
2. optical centre
3. first principal focus
4. second principal focus
5. focal length.

(i) Principal axis : “It is the line joining the centres of curvature of the two surfaces of the lens.”
(ii) Optical centre : It is a point on the principal axis of the lens such that a ray of light passing through this point emerges parallel to its direction of incidence.”

(iii) First principal focus : “Is is a point on the principal axis of a convex lens, such that the rays starting from it, after refraction travel parallel to the principal axis.”

(iv) Second Principal focus : “It is a point on the principal axis, such that rays coming parallel to the principal axis after refraction through the lens actually meet here.”

(v) Focal Length : “The distance between focus and optical centre of a lens is called focal lens.”

Question 3.
Draw neat diagrams for the formation of images in case of convex lens and state its characteristics when the object is :

1. at infinity
2. between 2F and infinity
3. at 2F
4. in between F and 2F
5. at F.

(i) Characteristics of image :

1. Real
2. Inverted
3. Highly diminished
4. at F on right side of lens.

(ii) Object between 2F and infinity : Image formed is

1. Real
2. Inverted
3. Diminished
4. Between F and 2F.

(iii) object at 2F

Image formed is :

1. Real
2. Inverted
3. At 2F on right side of lens
4. same size of object

(iv) Object lies between F and 2F :

Image formed is :

1. Real
2. Inverted
3. Magnified
4. Beyond 2F on Right side of lens.

(v) Object at F :

(i) at infinity (rays after passing lens become)
(ii) Real
(iii) Inverted parallel

Question 4.
Draw a neat diagram for a simple microscope.
Diagram of simple microscope :

When object lies between F and lens, its image is magnified, erect and on the same side of object which can be seen by eye. Hence this arrangement acts a simple microscope.

Question 5.
Draw neat diagrams for the formation of images in case of concave lens and state their characteristics when the object is :

1. at infinity
2. anywhere between infinity and the optical centre

(i) Object at infinity :

Image formed is

1. at second focus F2
2. virtual
3. erect
4. highly diminished.

(ii) Object lies anywhere between infinity and optical centre.

The image is formed between F and optical centre is virtual erect and diminished.

Question 6.
How will you find the focal length of a convex lens, by using a single pin and a plane mirror ?
Since rays after refraction through lens become parallel and ray after reflection from mirror meet at original point S, S is the focus and distance between S and lens is focal length. Even if the mirror is moved to any position, here at focal length, the parallel ray will meet at S (i.e. focus)

Question 7.
You are required to form an upright image of an object in case of (a) convex lens, (b) concave lens. What will be the position of the object with respect to the lens in each case ? Support your answer by diagrams and state the characteristics of the image in each case :
Upright image of an object incase of

(a) Convex lens : The position of object is between and optical centre.

(b) Concave lens : The position of object is anywhere between infinity and optical centre.

Multiple Choice Questions

Tick (✓) the most appropriate option.

1. The point on the principal axis of a convex lens, such that rays of light starting from it on passing through the lens, move parallel to the principal axis is called :
(a) first focal point
(b) second focal point
(c) optical centre
(d) aperture of lens
(a) first focal point

2. A convex lens can be regarded as a set of prisms and a glass slab, such that refracting angle of the prisms
(a) continuously decreases in outward direction
(b) continuously increases in outward direction
(c) remains same in outward direction
(d) none of these
(a) continuously decreases in outward direction

3. A lens forms an inverted image of an object equal to its own size. The object is :
(a) beyond infinity and 2F1
(b) at 2F1
(c) between 2F1 and F1
(d) in between F1 and optical centre
(b) at 2F1

4. A convex lens will form a virtual, erect and enlarged image, when the object is :
(a) between 2F1 and F1
(b) 2F1
(c) 2F1 and infinity
(d) F1 and optical centre
(d) F1 and optical centre

5. A concave lens always forms :
(a) real, inverted and enlarged image
(b) virtual, inverted and enlarged image
(c) virtual, erect and diminished image
(d) virtual, erect and enlarged image
(c) virtual, erect and diminished image

-: End of Refraction of Light : Goyal Brothers  ICSE Physics Class-10 Solution :-

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