# Refraction Through Lens ICSE Class-10 Concise Selina Solutions

Refraction Through Lens ICSE Class-10 Concise Physics Solutions Selina Publishers Chapter-5. We Provide Step by Step Answer of Exercise-5(A), MCQs-5(A), Exercise-5(B), MCQ-5(B), Exercise-5(C), MCQ-5(C), Numericals -5(C) , Exercise-5(D) and MCQ-5(D) Questions of Exercise-5 Refraction Through Lens ICSEClass-10 . Visit official Website CISCE  for detail information about ICSE Board Class-10.

 Board ICSE Publications Selina Publication Subject Physics Class 10th Chapter-5 Refraction Through Lens Book Name Concise Topics Solution of Exercise-5(A), MCQs-5(A), Exercise-5(B), MCQ-5(B), Exe-5(C), MCQ-5(C), Numericals -5(C) , Exe-5(D) and MCQ-5(D) Academic Session 2021-2022

## Refraction Through Lens ICSE Class-10 Concise Physics Solutions Selina Publishers Chapter-5.

-: Select Exercise :-

Exercise-5(A), MCQs-5(A), Exercise-5(B), MCQ-5(B),

Exe-5(C), MCQ-5(C), Numericals -5(C) , Exe-5(D) and MCQ-5(D)

Refraction Through Lens  “Selina Physics Solution”

### Exercise – 5 (A)

Page 109

#### Question 1

What is a lens?

A lens is a transparent refracting medium bounded by two curved surfaces which are generally spherical.

#### Question 2

Name the two kinds of lens? Draw diagrams to illustrate them.

Lenses are of two types :

(i)Convex or converging lens,

(ii)Concave or diverging lens.

#### Question 3

State difference between a convex and a concave lens in their (a) appearance, and (b) action on the incident light.

Convex lens:

(a) Thick in the middle thinner at the edges.

(b)

(i)It converge the incident rays towards the principal axis.

(ii)It has a real focus.

Concave lens:

(a) Thin in the middle thicker at the edges.

(i)It diverges the incident rays away from the principal axis.

(ii)It has a virtual focus.

#### Question 4

Which lens is converging:

(i) an equiconcave lens or an equiconvex lens?

(ii) A concavo-convex lens or a convexo-concave lens?

(a) Equiconvex lens is converging.

(b) The concavo-convex lens is a converging lens. This is because it is thicker at the middle and thinner at edges allowing it to converge all the light that is incident on it.

#### Question 5

Out of the two lenses, one concave and the other convex, state which one will show the divergent action on a light beam. Draw diagram to illustrate your answer.

Concave lens will show the divergent action on a light beam.

#### Question 6

Show by a diagram the refraction of two light rays incident parallel to the principal axis on a convex lens by treating it as a combination of a glass slab and two triangular glass prisms.

As shown in the figure the convex lens has two glass prisms and one glass slab. One of the glass prisms is situated above the glass slab and one below the slab.

#### Question 7

Show by a diagram the refraction of two light rays incident parallel to the principal axis on a concave lens by treating it as a combination of a glass slab and two triangular glass prisms.

As shown in the figure the concave lens has two glass prisms and one glass slab. One of the glass prisms is situated above the glass slab and one below the slab.

#### Question 8

How does the action of convex lens differ from that of a concave lens on a parallel beam of light incident on them? Draw diagrams to illustrate your answer.

If a parallel beam of light is incident on a convex lens then the upper part of the lens bends the incident ray downwards. The lower part bens the ray upwards while the central part passes the ray undeviated.

Convex lens

But in case of a concave lens the upper part of the lens bends the incident ray upwards and lower part bends the ray downwards while the central part passes the ray undeviated.

Concave lens

#### Question 9

Define the term principal axis of a lens.

It is the line joining the centers of curvature of the two surfaces of the lens.

#### Question 10

Explain optical centre of a lens with the help of a proper diagram(s).

It is 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.

It is marked by letter O in the figure. The optical centre is thus the centre of the lens.

#### Question 11

A ray of light incident on a point on the principal axis of a convex lens, passes undeviated through the lens. (a) What special name is given to this point on the principal axis? (b) Draw a labelled diagram to support answer in part(a).

(a) This point is known as Optical centre.

(b)

#### Question 12

State the condition when a lens is called an equiconvex or equiconcave.

A lens is called an equiconvex or equiconcave when radii of curvature of the two surfaces of lens are equal.

#### Question 13

Define the term principal foci of a convex lens and illustrate your answer with the aid of proper diagrams.

A light ray can pass through a lens from either direction. Therefore, a lens has two principal foci.

For a convex lens, the first focal point is a point F1 on the principal axis of the lens such that the rays of light starting from it or passing through it, after refraction through lens, become parallel to the principal axis of the lens.

The second focal point for a convex lens is a point F2 on the principal axis such that the rays of light incident parallel to the principal axis, after refraction from the lens, pass through it.

#### Question 14

Define the term principal foci of a concave lens and show them with the help of proper diagrams.

A light ray can pass through a lens from either direction. Therefore, a lens has two principal foci.

For a concave lens, the first focal point is a point F1 on the principal axis of the lens such that the incident rays of light appearing to meet at it, after refraction from the lens become parallel to the principal axis of the lens.

The second focal point for a concave lens is a point F2 on the principal axis of the lens such that the rays of light incident parallel to the principal axis, after refraction from the lens, appear to be diverging from this point.

#### Question 15

Draw a diagram to represent the second focus of a concave lens.

Concave lens representing second focus

#### Question 16

Draw a diagram to represent the second focus of a convex lens.

Convex lens representing second focus

#### Question 17

A ray of light, after refraction trough a concave lens emerges parallel to the principal axis.

(a) Draw a ray diagram to show the incident ray and its corresponding emergent ray.

(b) The incident ray when produced meets the principal axis at a point. Name the point F.

(a)

(b) The point where incident ray when produced meets the principal axis is called first focus.

#### Question 18

A ray of light after refraction through a convex lens emerges parallel to the principal axis. (a) Draw a ray diagram to show it. (b) The incident ray passes through a point F on the principal axis. Name the point F.

(a)

(b) The point where incident ray passes through a point on the principal axis is called first focus.

#### Question 19

A beam of light incident on a convex lens parallel to its principal axis converges at a point F on the principal axis. Name the point F. Draw a ray diagram to show it.

Such a point will be second focus.

#### Question 20

A beam of light incident on a thin concave lens parallel to its principal axis diverges and appears to come from a point F on the principal axis. Name the point F. Draw a ray diagram to show it.

It appears to come from ‘Second Focus’.

#### Question 21

Define the term focal length of a lens.

The distance from the optical centre O of the lens to its second focal point is called the focal length of the lens.

#### Question 22

What do you mean by focal plane of a lens?

A plane passing through the focal point and normal to the principal axis of the lens is called the first focal plane.

#### Question 23

State the condition for each of the following :

(a)a lens has both its focal length equal.

(b)a ray passes undeviated through the lens.

(a) If a lens has both its focal length equal medium is same on either side of lens.

(b) If a ray passes undeviated through the lens it is incident at the optical centre of the lens.

#### Question 24

A parallel oblique beam of light falls on a (i) convex lens, (ii) concave lens. Draw a diagram in each case to show the refraction of light through the lens.

Refraction of an oblique parallel beam by a convex lens.

Refraction of an oblique parallel beam by a concave lens

#### Question 25

The diagram below shows a lens as a combination of a glass block and two prisms

.

(i)Name the lens formed by the combination.

(ii)What is the line XX’ called?

(iii)Complete the ray diagram and show the path of the incident ray AB after passing through the lens.

(iv)The final emergent ray will either meet XX’ at a point or appear to come from a point on XX’. Label the point as F. What is this point called?

(i)The combination forms convex lens.

(ii)XX’ is known as principal axis.

(iii)The complete diagram is

(iv)The point F is called as Focal point or focus.

Page 110

#### Question 26

The diagram below shows a lens as a combination of a glass block and two prisms.

(i) Name the lens formed by the combination.

(ii) What is the line XX’ called?

(iii) Complete the path of the incident ray AB after passing through the lens.

(iv) The final emergent ray either meets XX’ at a point or appears to come from a point on XX’. Label it as F. What is this point called

(i) The combination forms concave lens.

(ii) XX’ is known as principal axis.

(iii) Complete diagram is drawn as

(iv) The point F is called as Focal point or focus.

#### Question 27

In Fig. 5.17 (a) and (b), F1 and F2 are the positions of the two foci of the thin lenses. Draw the path taken by the light ray AB after it emerges from the lens.

(a)

(b)

#### Question 28

In Fig 5.18 . (a) and (b), F1 and F2 are the two foci of the thin lenses and AB is the incident ray. Complete the diagram to show the path of the ray AB after refraction through each lens.

#### Question 29

Complete the following sentences :

(a) If half part of a convex lens is covered, the focal length __________ change, but the intensity of image _________.

(b) A convex lens is placed in water. Its focal length will ________.

(c)The focal length of a thin convex lens is _________ than that of a thick convex lens.

(a) If half part of a convex lens is covered, the focal length does not change, but the intensity of image decreases.

(b) A convex lens is placed in water. Its focal length will increase.

(c) The focal length of a thin convex lens is more than that of a thick convex lens.

### Multiple Choice Type – 5 ( A)

Page 110

#### Question 1

A ray of light after refraction through a lens emerges parallel to the principal axis of the lens. The incident ray either passes through :

(a)  its optical centre

(b) its first focus

(c) its second focus

(d) its centre of curvature of the first surface

(b) its first focus

#### Question 2

A ray of light incident on a lens parallel to its principal axis, after refraction passes through or appears to come from:

(a) Its first focus

(b) Its optical entre

(c) Its second focus

(d) The centre of curvature of its second surface

(C) Its second focus

### Exercise – 5( B)

Page 119

#### Question 1

What are the three principal rays that are drawn to construct the ray diagram for the image formed by a lens? Draw diagram to support your answer.

(i) A ray of light incident at the optical centre O of the lens passes undeviated through the lens.

(ii) A ray of light incident parallel to the principal axis of the lens, after refraction passes through the second focus F2 (in a convex lens) or appears to come from the second focus F2 (in a concave lens).

(iii) A ray of light passing through the first focus F1 (in a convex lens) or directed towards the first focus F1 (in a concave lens), emerges parallel to the principal axis after refraction.

#### Question 2

In the diagrams below, XX’ represents the principal axis, O the optical centre and F the focus of the lens. Complete the path of rays A and B as they emerge out of the lens.

#### Question 3

Where must a point source of light be placed in front of a convex lens so as to obtain a parallel beam of light?

If the point source of light is placed at the ‘first focal point’ (i.e. the focal point on the left of the optical centre of the convex lens), then the rays of light after being refracted through the length obtain a parallel beam of light.

#### Question 4

Distinguish between a real and a virtual image.

 Real image Virtual image 1.A real image is formed due to actual intersection of refracted (or reflected) rays. 1A virtual image is formed when the refracted (or reflected) rays meet if they are produced backwards. 2A real image can be obtained on a screen. 2.A virtual image can not be obtained on a screen. 3.A real image is inverted with respect to the object. 3.A virtual image is erect with respect to the object.

#### Question 5

Study the diagram given below.

(a) Name the lens LL’.

(b) What are the points O and O’ called?

(c) Complete the diagram to form the image of the object AB.

(d) State the three characteristics of the image.

(e) Name a device in which this action of lens is used.

(a) LL’ lens is convex lens.

(b) O and O’ are known as first and second focal points respectively.

(c)

(d) The image formed will be magnified, virtual and upright.

(e) Such action of lens is used in a magnifying glass.

Page 120

#### Question 6

Study the diagram below.

(i)Name the lens LL’.

(ii)What are the points O, O’ called?

(iii)Complete the diagram to from the image of the object AB.

(iv)State three characteristics of the image.

(i) LL’ is concave lens.

(ii)The points O and O’ are called second and first focal points respectively.

(iii)

(iv)The three characteristics of the image are :

Virtual

Erect

Diminished

#### Question 7

The following diagram in Fig.5.50  shows an object AB and a converging lens L with foci F1 and F2.

(a) Draw two rays from the object AB and complete the diagram to locate the position of the image CD. Also mark on the diagram the position of eye from where the image can be viewed.

(b) State three characteristics of the image in relation to the object.

(a)The complete diagram is

(b)The image formed will be magnified, virtual and upright.

#### Question 8

The diagram given below in fig. shows the position of an object OA in relation to a converging lens whose foci are at F1 and F2.

(i) Draw two rays to locate the position of the image.

(ii) State the position of image with reference to the lens.

(iii) Describe the three characteristics of the image.

(iv) Describe how the distance of the image from the lens and the size of the image change as the object move towards F1.

(i)

(ii) The position of the images will be more than twice the focal length of lens.

(iii) The image will be magnified, real and inverted.

(iv) As the object move towards F1 the image will shift away from F2 and it is magnified. At Fthe image will form at infinity and it is highly magnified. Between F1 and optical centre, the image will form on the same side of object and will be magnified.

#### Question 9

A converging lens forms the image of an object placed in front of it, beyond 2F2 of the lens.

(a) Where is the object placed? (b) Draw a ray diagram to show the formation of image. (c) State its three characteristics of the image.

(a) The object is placed between 2F1. and . F1

(b)

(c) Three characteristics of the image.

1. The image is formed beyond 2F2.
2.  image will be magnified,
3.  real and inverted.

#### Question 10

A convex lens forms an image of an object equal to the size of the object. (a) Where is the object placed in front of the lens? (b) Draw a diagram to illustrate it. (c) State two more characteristics of the image.

(a) The object is placed at the centre of curvature.

(b)

(c) The image formed is real and inverted.

#### Question 11

A lens forms an erect, magnified and virtual image of an object.

(a) Name the kind of lens.

(b) Where is the object placed in relation to the lens?

(c) Draw a ray diagram to show the formation of image.

(d) Name the device which uses this principle.

(a) Convex lens

(b) The object is placed between the lens and focus (F1).

(c)

(d) ‘Magnifying glass’ uses this principle.

#### Question 12

A lens forms an image between the object and the lens. (a) name the lens. (b) Draw a ray diagram to shown the formation of such image. (c) state three characteristics of the image.

(a) The lens that forms the image between the object and itself is a concave lens.

(b) Ray diagram:

(c) The image formed is virtual, erect and diminished.

#### Question 13

Classify as real or virtual, the image of a candle flame formed on a screen by a convex lens. Draw a ray diagram to illustrate how the image is formed.

Let the candle is placed beyond 2F1 and its diminished image which is real and inverted is formed between F2 and 2F2.

Here the candle is AB and its real and inverted image is formed between F2 and 2F2.

#### Question 14

Show by a diagram that a diverging lens cannot form a real image of an object placed anywhere on its principal axis.

#### Question 15

Draw a ray diagram to show how a converging lens can form a real and enlarged image of an object.

The image formed in above diagram is real, enlarged and inverted.

#### Question 16

A lens forms an upright and diminished image of an object placed at its focal point. Name the lens and draw a ray diagram to show the formation of image.

If a lens forms an upright and diminished image of an object placed at its focal point, then it is a concave lens.

#### Question 17

Draw a ray diagram to show how a converging lens is used as a magnifying glass to observe a small object. Mark on your diagram the foci of the lens and the position of the eye.

The object is placed between focal point F1 and convex lens and its image is formed at the same side of the lens which is enlarged.

So this lens can be used as a magnifying lens.

Question 18

Draw a ray diagram to show how a converging lens is can form an image of the sun. Hence give a reason for the term ‘burning glass’ for a converging lens used in this manner.

The sun is at infinity so convex lens forms its image at second focal point which is real and very much diminished in size.

While using the convex lens as burning glass, the rays of light from the sun (at infinity) are brought to focus on a piece of paper kept at the second focal plane of the lens. Due to sufficient heat of the sun rays, the paper burns. Hence this lens is termed as ‘burning glass’.

Page 121

#### Question 19

A lens forms an inverted image of an object.

(a) Name the kind of lens.

(b) State the nature of the image whether real or virtual?

(a) This is convex lens.

(b) The nature of the image is real.

#### Question 20

A lens forms an upright and magnified image of an object.

(a)Name the lens.

(b)Draw a labelled ray diagram to show the image formation.

(a)Convex lens.

(b)Virtual.

#### Question 21

(a)Name the lens which always forms an erect and virtual image.

(b)State whether the image in part (a) is magnified or diminished?

(a)Concave lens

(b)Image is diminished

#### Question 22

Can a concave lens form an image of size two times that of the object? Give reason?

A concave lens cannot form an image two times that of the object because it always forms a diminished image.

#### Question 23

Give two characteristics of the image formed by a concave lens.

Image formed by a concave lens is virtual and diminished.

#### Question 24

Give two characteristics of the virtual image formed by a convex lens.

The virtual image formed by a convex lens will be magnified and upright.

#### Question 25

In each of the following cases, where must an object be placed in front of a convex lens so that the image formed is

(a)at infinity,

(b)of same size as the object,

(c)inverted and enlarged,

(d)upright and enlarged?

(a)at focus,

(b)at 2F,

(c)between F and 2F,

(d)between optical centre and focus.

#### Question 26

Complete the following table:

 Type of lens Position of object Nature of image Size of image Convex Between optic centre and focus Convex At focus Concave At infinity Concave At any distance

 Type of lens Position of object Nature of image Size of image Convex Between optic centre and focus Virtual and upright Magnified Convex At focus Real and inverted Very much magnified Concave At infinity Virtual and upright Highly diminished Concave At any distance Virtual and upright Diminished

#### Question 27

State the changes in the position, size and nature of the image of an object when brought form infinity up to a convex lens. Illustrate your answer by drawing the ray diagrams.

(i)When the object is situated at infinity, the position of image is at F2, it is very much diminished in size and it is real and inverted.

(ii)When the object (AB) is situated beyond 2F1, the position of image (A’B’) is between F2 and 2F2, it is diminished in size and real and inverted.

(iii)When the object (AB) is situated at 2F1, the position of image (A’B’) is at 2F2, it is of same size as the object and real and inverted.

(iv)When the object (AB) is situated between 2F1and F1, the position of image (A’B’) is beyond 2F2, it is magnified in size and real and inverted.

(v)When the object (AB) is situated at F1, the position of image is at infinity; it is very much magnified in size and real and inverted.

(vi)When the object (AB) is situated between lens and F1, the position of image (CD) is on the same side, behind the object; it is magnified in size and virtual and upright.

#### Question 28

State the changes in the position, size and nature of the image When the object is brought from infinity up to a concave lens. Illustrate your answer by drawing diagrams.

(i)When object (AB) is situated at infinity then parallel rays from object appears to fall on concave lens. Due to which image forms at focus. This image is highly diminished in size and virtual and upright.

(ii)When object (AB) is situated at any point between infinity and optical centre of the lens then image forms between focus and optical centre. This image is diminished in size and virtual and upright.

#### Question 29

Complete the following sentences:

(a)An object is placed at a distance of more than 40 cm from a convex lens of focal length 20 cm. The image formed is real, inverted and…………….

(b)An object is placed at a distance 2f from a convex lens of focal length f. The image formed is…………….that of the object.

(c)An object is placed at a distance 5 cm from a convex lens of focal length 10 cm. The image formed is virtual, upright and…………..

(a)An object is placed at a distance of more than 40 cm from a convex lens of focal length 20 cm. The image formed is real, inverted and diminished.

(b)An object is placed at a distance 2f from a convex lens of focal length f. The image formed is equal to that of the object.

(c)An object is placed at a distance 5 cm from a convex lens of focal length 10 cm. The image formed is virtual, upright and magnified.

#### Question 30

State whether the following statements are ‘true’ or ‘false’ by writing T/F against them.

(a)A convex lens has a divergent action and a concave lens has a convergent action.

(b)A concave lens if kept at a proper distance from an object can form its real image.

(c)A ray of light incident parallel to the principal axis of a lens, passes undeviated after refraction.

(d)A ray of light incident at the optical centre of lens, passes undeviated after refraction.

(e)A concave lens forms a magnified or diminished image depending on the distance of object from it.

(a)False

(b)False

(c)False

(d)True

(e)False

Refraction Through Lens

### Multiple Choice Type – 5(B)

Page 121

#### Question 1

For an object placed at distance 20 cm in front of a convex lens, the image is at distance 20 cm behind the lens. The focal length of convex lens is:

(a) 20 cm

(b) 10 cm

(c) 15 cm

(d) 40 cm

The focal length of the convex lens is 10 cm.

Hint: As the object distance = image distance, the object must be kept at 2f.

Therefore, 2f = 20 cm or f = 10 cm.

#### Question 2

For the object placed between optical centre and focus of a convex lens, the image is:

(a) Real and enlarged

(b) Real and diminished

(c) Virtual and enlarged

(d) Virtual and diminished.

Virtual and enlarged.

Explanation: When the object is kept between optical centre and focus of a convex lens, the image is formed on the same side, behind the object. The image thus formed is virtual, enlarged and erect.

#### Question 3

A concave lens forms the image of an object which is:

(a) Virtual, inverted and diminished

(b) Virtual, upright and diminished

(c) Virtual, inverted and enlarged

(d) Virtual, upright and enlarged