# Lakhmir Singh solutions for Class 10 Physics (Science) chapter 5 - Refraction of Light [Latest edition]

#### Chapters ## Solutions for Chapter 5: Refraction of Light

Below listed, you can find solutions for Chapter 5 of CBSE Lakhmir Singh for Class 10 Physics (Science).

Exercise 1Exercise 2Exercise 3Exercise 4Exercise 5Exercise 6Exercise 7
Exercise 1 [Pages 219 - 221]

### Lakhmir Singh solutions for Class 10 Physics (Science) Chapter 5 Refraction of Light Exercise 1 [Pages 219 - 221]

Exercise 1 | Q 1 | Page 219

If a ray of light goes from a rarer medium to a denser medium, will it bend towards the normal or away from it?

Exercise 1 | Q 1 | Page 219

A beam of light travelling in a rectangular glass slab emerges into air. Draw a ray-diagram indicating the change in its path.

Exercise 1 | Q 1 | Page 219

If a ray of light goes from a rarer medium to a denser medium, will it bend towards the normal or away from it?

Exercise 1 | Q 2 | Page 219

If a ray of light goes form a denser medium to a rarer medium, will it bend towards the normal or away from the normal?

Exercise 1 | Q 4 | Page 219

A beam of light travelling in air is incident of water. Draw a ray-diagram indicating the change in its path in water.

Exercise 1 | Q 5 | Page 219

A ray of light travelling in water emerges into air. Draw a ray-diagram indicating the change in its path.

Exercise 1 | Q 5 | Page 219

A ray of light travelling in water emerges into air. Draw a ray-diagram indicating the change in its path.

Exercise 1 | Q 6 | Page 219

A ray of light travelling in air is incident on a parallel-sided glass slab (or rectangular glass slab). Draw a ray-diagram indicating the change in its path in glass.

Exercise 1 | Q 7 | Page 219

A ray of light travelling in glass emerges into air. State whether it will bend towards the normal or away from the normal.

Exercise 1 | Q 8 | Page 219

A ray of light travelling in air enters obliquely into water. Does the light ray bend towards the normal or away from the normal? Why?

Exercise 1 | Q 9 | Page 219

A ray of light goes from water into air. Will it bend towards the normal or away from the normal?

Exercise 1 | Q 10 | Page 219

State two effects caused by the refraction of light.

Exercise 1 | Q 11 | Page 219

Name the phenomenon due to which a swimming pool appears less deep than it really is.

Exercise 1 | Q 12 | Page 219

When a ray of light passes from air into glass, is the angle of refraction greater than or less than the angle of incidence?

Exercise 1 | Q 13 | Page 220

A ray of light passes from air into a block of glass. Does it bend towards the normal or away from it?

Exercise 1 | Q 14 | Page 220

As light rays pass from water into glass, are they refracted towards the normal or away from the normal?

Exercise 1 | Q 15 | Page 220

In which material do you think light rays travel faster-glass or air?

Exercise 1 | Q 16 | Page 220

Which phenomenon of light makes the water to appear shallower than it really is?

Exercise 1 | Q 17 | Page 220

State whether the following statement is true or false:
Refraction occurs because light slows down in denser materials.

Exercise 1 | Q 18 | Page 220

Why does a ray of light bend when it travels from one medium to another?

Exercise 1 | Q 19.1 | Page 220

Fill in the following blank with suitable word:

Light travelling along a normal is ...............refracted.

Exercise 1 | Q 19.2 | Page 220

Fill in the following blank with suitable word:

Light bends when is passes from water into air. We say that it is ............

Exercise 1 | Q 20 | Page 220

What is meant by 'refraction of light'? Draw a labelled ray diagram to show the refraction of light.

Exercise 1 | Q 20 | Page 220

What is meant by 'refraction of light'? Draw a labelled ray diagram to show the refraction of light.

Exercise 1 | Q 21 | Page 220

A ray of light travelling in air is incident on a rectangular glass block and emerges out into the air from the opposite face. Draw a labelled ray diagram to show the completer path of this ray of light. Mark the two points where the refraction of light takes place. What can you say about the final direction of ray of light?

Exercise 1 | Q 22.1 | Page 220

Draw a labelled ray diagram to show how a ray of light is refracted when it passes:

from air into an optically denser medium.

Exercise 1 | Q 22.2 | Page 220

Draw a labelled ray diagram to show how a ray of light is refracted when it passes:

from an optically denser medium into air.

Exercise 1 | Q 23 | Page 220

The diagram given alongside shows a ray of light entering a rectangular block of glass.

(a) Copy the diagram and draw the normal at the point of entry.
(b) Draw the approximate path of the ray of light through the glass block and out of the other side.

Exercise 1 | Q 23 | Page 220

The diagram given alongside shows a ray of light entering a rectangular block of glass.

(a) Copy the diagram and draw the normal at the point of entry.
(b) Draw the approximate path of the ray of light through the glass block and out of the other side.

Exercise 1 | Q 24.1 | Page 220

What is meant by the 'angle of incidence' and the 'angle of refraction' for a ray of light?

Exercise 1 | Q 24.2 | Page 220

Draw a labelled ray diagram to show the angle of incidence and the angle of refraction for a refracted ray of light.

Exercise 1 | Q 25.1 | Page 220

Light travels more quickly through water than through glass.

Which is optically denser : water or glass?

Exercise 1 | Q 25.2 | Page 220

Light travels more quickly through water than through glass.

If a ray of light passes from glass into water, which way will it bend : towards the normal or away from the normal?

Exercise 1 | Q 26.1 | Page 220

Draw a labelled ray diagram to show how a ray of light passes through a parallel sided glass block:

if it hits the glass block at 90° (that is, perpendicular to the glass block)

Exercise 1 | Q 26.2 | Page 220

Draw a labelled ray diagram to show how a ray of light passes through a parallel sided glass block:

if it hits the glass block at an angle other than 90° (that is, obliquely to the glass block).

Exercise 1 | Q 28.1 | Page 220

Explain why, a stick half immersed in water appears to be bent at the surface. Draw a labelled diagram to illustrate your answer.

Exercise 1 | Q 29 | Page 220

With the help of a labelled diagram, explain why a tank full of water appears less deep than it actually is.

Exercise 1 | Q 29 | Page 220

With the help of a labelled diagram, explain why a tank full of water appears less deep than it actually is.

Exercise 1 | Q 29.1 | Page 220

With the help of a labelled diagram, explain why a tank full of water appears less deep than it actually is.

Exercise 1 | Q 29.2 | Page 220

Name the phenomenon due to which a pencil partly immersed in water and held obliquely appears to be bent at the water surface.

Exercise 1 | Q 30.1 | Page 220

Show the lateral displacement of the ray on the diagram.

Exercise 1 | Q 30.1 | Page 220

With the help of a diagram, show how when light falls obliquely on the side of a rectangular glass slab, the emergent ray is parallel to the incident ray.

Exercise 1 | Q 30.3 | Page 220

State two factors on which the lateral displacement of the emergent ray depends.

Exercise 1 | Q 31 | Page 220

Explain with the help of a labelled ray diagram, why a pencil partly immersed in water appears to be bent at the water surface. State whether the bending of pencil will increase or decrease if water is replaced by another liquid which is optically more dense than water. Give reason for your answer.

Exercise 1 | Q 32 | Page 221

Light travelling from a denser medium to a rarer medium along a normal to the boundary:

(a) is refracted towards the normal
(b) is refracted away from the normal
(c) goes along the boundary
(d) is not refracted

Exercise 1 | Q 33 | Page 221

A ray of light passes from glass into air. The angle of refraction will be:

(a) equal to the angle of incidence
(b) greater than the angle of incidence
(c) smaller than the angle of incidence
(d) 45°

Exercise 1 | Q 34 | Page 221

A ray of light travelling in air goes into water. The angle of refraction will be:

(a) 90°
(b) smaller than the angle of incidence
(c) equal to the angle of incidence
(d) greater than the angle of incidence

Exercise 1 | Q 35 | Page 221

The speed of light in air is:

(a) 3 × 108 cm/s
(b) 3 × 108 mm/s
(c) 3 × 108 km/s
(d) 3 × 108 m/s

Exercise 1 | Q 36 | Page 221

When a ray of light travelling in glass enters into water obliquely:

(a) it is refracted towards the normal
(b) it is not refracted at all
(c) it goes along the normal
(d) it is refracted away from the normal

Exercise 1 | Q 37 | Page 221

A ray of light travelling in water falls at right angles to the boundary of a parallel-sided glass block. The ray of light:

(a) is refracted towards the normal
(b) is refracted away from the normal
(c) does not get refracted
(d) is reflected along the same path

Exercise 1 | Q 38 | Page 221

A ray of light passes from a medium X to another medium Y. No refraction of light occurs if the ray of light hits the boundary of medium Y at an angle of:

(a) 0°
(b) 45°
(c) 90°
(d) 120°

Exercise 1 | Q 39 | Page 221

Which of the following diagrams shows the ray of light refracted correctly?

Exercise 1 | Q 40.1 | Page 221

A vertical ray of light strikes the horizontal surface of some water:

What is the angle of incidence?

Exercise 1 | Q 40.2 | Page 221

A vertical ray of light strikes the horizontal surface of some water:

What is the angle of refraction?

Exercise 1 | Q 41 | Page 221

How is the reflection of light ray from a plane mirror different from the refraction of light ray as it enters a block of glass?

Exercise 1 | Q 42.1 | Page 221

How does the light have to enter the glass:

to produce a large amount of bending?

Exercise 1 | Q 42.2 | Page 221

How does the light have to enter the glass:

for no refraction to happen?

Exercise 1 | Q 43.1 | Page 221

How can you bend light away from the normal?

Exercise 1 | Q 43.2 | Page 221

How must light travel out of a substance if it is not going to be refracted?

Exercise 1 | Q 44 | Page 221

Draw and complete the following diagrams to show what happens to the beams of light as they enter the glass block and then leave it:

Exercise 1 | Q 44 | Page 221

Draw and complete the following diagrams to show what happens to the beams of light as they enter the glass block and then leave it:

Exercise 1 | Q 45 | Page 221

Why does a beam of light when it enters glass at an angle? Why does it not bend if it inters the glass at right angles?

Exercise 2 [Pages 227 - 229]

### Lakhmir Singh solutions for Class 10 Physics (Science) Chapter 5 Refraction of Light Exercise 2 [Pages 227 - 229]

Exercise 2 | Q 1 | Page 227

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

Exercise 2 | Q 2 | Page 227

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

Exercise 2 | Q 3 | Page 228

What is the unit of refractive index?

Exercise 2 | Q 4 | Page 228

Which has higher refraction index :  water of glass?

Exercise 2 | Q 5 | Page 228

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

Exercise 2 | Q 6 | Page 228

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

Exercise 2 | Q 7 | Page 228

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

Exercise 2 | Q 8 | Page 228

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

Exercise 2 | Q 9 | Page 228

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.

Exercise 2 | Q 10 | Page 228

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

Exercise 2 | Q 10 | Page 228

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

Exercise 2 | Q 11 | Page 228

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° = 0.540).

Exercise 2 | Q 12 | Page 228

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

 Medium Speed of light Vacuum 3.00 × 108 m/s Flint glass 1.86 × 108 m/s Crown glass 1.97 × 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.

Exercise 2 | Q 13 | Page 228

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:

(aair nx
(bair nY
(cx n

Exercise 2 | Q 14 | Page 228

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?

Exercise 2 | Q 14 | Page 228

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?

Exercise 2 | Q 16 | Page 228

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.

Exercise 2 | Q 17 | Page 228

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

Exercise 2 | Q 18.1 | Page 228

State and explain the laws of refraction of light with the help of a labelled diagram.

Exercise 2 | Q 18.2 | Page 228

What is meant by the refractive index of a substance?

Exercise 2 | Q 18.3 | Page 228

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.

Exercise 2 | Q 19 | Page 228

The refractive indices of four substance P, Q, R and S are 1.50, 1.36, 1.77 and 1.31 respectively. The speed of light is the maximum in the substance:

(aP
(bQ
(cR
(d

Exercise 2 | Q 20 | Page 228

The refractive indices of four materials A, B, C and D are 1.33, 1.43, 1.71 and 1.52 respectively. When the light rays pass from air into these materials, they refract the maximum in:

(a) material A
(b) material B
(c) material C
(d) material D

Exercise 2 | Q 21 | Page 229

The refractive index of glass for light going from air to glass is  The refractive index for light going from glass to air will be:

(a) 1/3

(b) 4/5
(c) 4/6
(d) 5/2

Exercise 2 | Q 22 | Page 229

The refractive index of glass for light going from air to glass is .

The refractive index for light going from glass to air will be:

(a) 1/3

(b) 4/5
(c) 4/6
(d) 5/2

Exercise 2 | Q 23 | Page 229

The speed of light in substance X is 1.25 × 108 m/s and that in air is 3 × 108 m/s. The refractive index of this substance will be:

(a) 2.4
(b) 0.4
(c) 4.2
(d) 3.75

Exercise 2 | Q 24 | Page 229

The refractive indexes of four substances P, Q, R and S are 1.77, 1.50, 2.42 and 1.31 respectively. When light travelling in air is incident on these substances at equal angles, the angle of refraction will be the maximum in:

(a) substance P
(b) substance Q
(c) substance R
(d) substance S

Exercise 2 | Q 25 | Page 229

The refractive index of water is:

(a) 1.33
(b) 1.50
(c) 2.42
(d) 1.36

Exercise 2 | Q 26 | Page 229

The refractive index of water with respect to air is 4/3. The refractive index of air with respect to water will be:

(a) 1.75
(b) 0.50
(c) 0.75
(d) 0.25

Exercise 2 | Q 27 | Page 229

Refractive indices of water, sulphuric acid, glass and carbon disulphide are 1.33, 1.43, 1.53 and 1.63 respectively. the light travels slowest in:

(a) sulphuric acid
(b) glass
(c) water
(d) carbon disulphide

Exercise 2 | Q 27 | Page 229

Refractive indices of water, sulphuric acid, glass and carbon disulphide are 1.33, 1.43, 1.53 and 1.63 respectively. the light travels slowest in:

(a) sulphuric acid
(b) glass
(c) water
(d) carbon disulphide

Exercise 2 | Q 28 | Page 229

The refractive index of glass with respect to air is 3/2 and the refractive index of water with respect to air is 4/3. The refractive index of glass with respect to water will be:

(a) 1.525
(b) 1.225
(c) 1.425
(d) 1.125

Exercise 2 | Q 29 | Page 229

The following table gives the refractive indices of a few media:

 1 2 3 4 5 Medium Water Crown glass Rock salt Ruby Diamond Refractive index 1.33 1.52 1.54 1.71 2.42

Use this table to give an example of:

(i) a medium pair so that light speeds up when it goes from one of these medium to another.
(ii) a medium pair so that light slows down when it goes from one of these medium to another.

Exercise 2 | Q 30 | Page 229

Refractive indices of four media A, B, C and D are given below:

 Medium Refractive index A 1.33 B 1.44 C 1.52 D 1.65

In which of these four media is the speed of light (i) maximum, and (ii) minimum?

Exercise 3 [Pages 239 - 242]

### Lakhmir Singh solutions for Class 10 Physics (Science) Chapter 5 Refraction of Light Exercise 3 [Pages 239 - 242]

Exercise 3 | Q 1 | Page 239

Name the lens which can concentrate sun's rays to a point and burn a hole in a piece of paper.

Exercise 3 | Q 2 | Page 239

Give the usual name for the following:
A point inside a lens through which the light passes undeviated.

Exercise 3 | Q 3 | Page 239

A 1 cm high object is placed at a distance of 2f from a convex lens. What is the height of the image formed?

Exercise 3 | Q 4 | Page 239

f the image formed by a convex lens is of the same size as that of the object, what is the position of the image with respect to the lens?

Exercise 3 | Q 4 | Page 239

f the image formed by a convex lens is of the same size as that of the object, what is the position of the image with respect to the lens?

Exercise 3 | Q 5 | Page 239

If an object is placed at the focus of a convex lens, where is the image formed?

Exercise 3 | Q 6 | Page 239

Where should an object be placed in order to use a convex lens as a magnifying glass?

Exercise 3 | Q 7 | Page 239

Where should an object be placed in front of a convex lens so as to obtain its virtual, erect and magnified image?

Exercise 3 | Q 8 | Page 239

Where should an object be placed in front of a convex lens so as to obtain its real, inverted and magnified image?

Exercise 3 | Q 9 | Page 239

For what position of an object a real, diminished image is formed by a convex lens?

Exercise 3 | Q 10 | Page 239

If an object is at a considerable distance (or infinity) in front of a convex lens, where is the image formed?

Exercise 3 | Q 11 | Page 240

Draw the given diagram in your answer book and complete it for the path of a ray of light after passing through the lens.

Exercise 3 | Q 12 | Page 240

What type of lens would you use as a magnifying glass? How close  must the object be to the lens?

Exercise 3 | Q 13 | Page 240

Name two factors on which the focal length of a lens depends.

Exercise 3 | Q 14 | Page 240

State any two uses of convex lenses.

Exercise 3 | Q 15.1 | Page 240

Fill in the following blank with suitable word:

Parallel rays of light are refracted by a convex lens to a point called the ........

Exercise 3 | Q 15.2 | Page 240

Fill in the following blank with suitable word:

The image in a convex lens depends upon the distance of the ........... from the lens.

Exercise 3 | Q 16.1 | Page 240

What is a lens?

Exercise 3 | Q 16.2 | Page 240

Distinguish between a convex lens and concave lens. Which of the two is a converging lens : convex lens of concave lens?

Exercise 3 | Q 17 | Page 240

Explain with the help of a diagram, why the convex lens is also called a converging lens.

Exercise 3 | Q 17.1 | Page 240

Explain with the help of a diagram, why the convex lens is also called a converging lens.

Exercise 3 | Q 17.2 | Page 240

Define principal axis, principal focus and focal length of a convex lens.

Exercise 3 | Q 18.1 | Page 240

Explain with the help of a diagram, why the concave lens is also called a diverging lens.

Exercise 3 | Q 18.2 | Page 240

Define the principal focus of a concave lens.

Exercise 3 | Q 19 | Page 240

Draw a ray diagram to show the formation of a real magnified image by a convex lens. (In your sketch the position of object and image with respect to the principal focus of lens should be shown clearly).

Exercise 3 | Q 20 | Page 240

Describe with the help of a ray-diagram, the formation of image of a finite object placed in front of convex lens between f and 2f. Give two characteristics of the image so formed.

Exercise 3 | Q 21 | Page 240

Describe with the help of a ray diagram the nature, size and position of the image formed when an object is placed in front of a convex lens between focus and optical centre. State three characteristics of the image formed.

Exercise 3 | Q 22 | Page 240

An object is placed at a distance equal to 2f in front of a convex lens. Draw a labelled ray diagram to show the formation of image. State two characteristics of the image formed.

Exercise 3 | Q 23 | Page 240

Describe with the help of a ray-diagram, the size, nature and position of the image formed by a convex lens when an object is placed beyond 2f in front of the lens.

Exercise 3 | Q 23 | Page 240

Describe with the help of a ray-diagram, the size, nature and position of the image formed by a convex lens when an object is placed beyond 2f in front of the lens.

Exercise 3 | Q 24 | Page 240

Describe with the help of a ray diagram the nature, size and position of the image formed when an object is placed at infinity (considerable distance) in front of a convex lens. State three characteristics of the image so formed.

Exercise 3 | Q 25.1 | Page 240

What type of lens is shown in the diagram on the right? What will happen to the parallel rays of light? Show by completing the ray diagram.

Exercise 3 | Q 25.2 | Page 240

You eye contains a convex lens. Why is it unwise to look at the sun?

Exercise 3 | Q 26.1 | Page 240

Where must the object be placed for the image formed by a converging lens to be:

real, inverted and smaller than the object?

Exercise 3 | Q 26.3 | Page 240

Where must the object be placed for the image formed by a converging lens to be:

real, inverted and larger than the object?

Exercise 3 | Q 26.4 | Page 240

Where must the object be placed for the image formed by a converging lens to be:

virtual, upright and larger than the object?

Exercise 3 | Q 26.4 | Page 240

Where must the object be placed for the image formed by a converging lens to be:

real, inverted and same size as the object?

Exercise 3 | Q 27 | Page 240

Draw a diagram to show how a converging lens held close to the eye acts as a magnifying glass. Why is it usual to choose a lens of short focal length for this purpose rather than one of long focal length?

Exercise 3 | Q 28 | Page 240

How could you find the focal length of a convex lens rapidly but approximately?

Exercise 3 | Q 29.1 | Page 240

With the help of a labelled diagram explain how a convex lens converges a beam of parallel light rays. Mark the principal axis, optical centre, principal focus and focal length of the convex lens on the diagram.

Exercise 3 | Q 29.2 | Page 240

State whether convex lens has a real focus or a virtual focus.

Exercise 3 | Q 29.3 | Page 240

List some things that convex lens and concave mirror have in common.

Exercise 3 | Q 30.1 | Page 241

With the help of a labelled diagram, explain how a concave lens diverges a beam of parallel light rays. Mark the principal axis, optical centre, principal focus and focal length of the concave lens on the diagram.

Exercise 3 | Q 30.2 | Page 241

State whether concave lens has a real focus or a virtual focus.

Exercise 3 | Q 30.3 | Page 241

List some things that concave lens and concave mirror have in common.

Exercise 3 | Q 31.1 | Page 241

Draw ray diagrams to represent the nature, position and relative size of the image formed by a convex lens for the object placed:

at 2F1

Exercise 3 | Q 31.2 | Page 241

Draw ray diagrams to represent the nature, position and relative size of the image formed by a convex lens for the object placed:

between F1 and the optical centre O of the lens.
Which of the above two cases shows the use of convex lens as a magnifying glass? Give reasons for your choice.

Exercise 3 | Q 32.1 | Page 241

An object is placed well outside the principal focus of a convex lens. Draw a ray diagram to show how the image is formed, and say whether the image is real or virtual.

Exercise 3 | Q 32.2 | Page 241

What is the effect on the size and position of the image of moving the object (i) towards the lens, and (ii) away from the lens?

Exercise 3 | Q 33.1 | Page 241

Explain what is meant by a virtual, magnified image.

Exercise 3 | Q 33.2 | Page 241

Draw a ray diagram to show the formation of a virtual magnified image of an object by a convex lens. In your diagram, the position of object and image with respect to the principal focus should be shown clearly.

Exercise 3 | Q 33.3 | Page 241

Three convex lenses are available having focal lengths of 4 cm, 40 cm and 4 m respectively. Which one would you choose as a magnifying glass and why?

Exercise 3 | Q 34.1 | Page 241

Explain why, a real image can be projected on a screen but a virtual image cannot.

Exercise 3 | Q 34.3 | Page 241

Name one simple optical instrument in which the above arrangement of convex lens is used.

Exercise 3 | Q 35 | Page 241

A convex lens has a focal length of 10 cm. At which of the following position should an object be placed so that this convex lens may act as a magnifying glass?

(a) 15 cm
(b) 7 cm
(c) 20 cm
(d) 25 cm

Exercise 3 | Q 36 | Page 241

Which one of the following materials cannot be used to make a lens?

• Water

• Glass

• Plastic

• Clay

Exercise 3 | Q 37 | Page 241

A small bulb is placed at the focal point of a converging lens. When the bulb is switched on, the lens produces:

(a) a convergent beam of light
(b) a divergent beam of light
(c) a parallel beam of light
(d) a patch of coloured light

Exercise 3 | Q 38 | Page 241

An illuminated object is placed at a distance of 20 cm from a converging lens of focal length 15 cm. The image obtained on the screen is:

(a) upright and magnified
(b) inverted and magnified
(c) inverted and diminished
(d) upright and diminished

Exercise 3 | Q 39 | Page 241

An object is placed f and 2f of a convex lens. Which of the following statements correctly describes its image?

(a) real, larger than the object
(b) erect, smaller than the object
(c) inverted, same size as object
(d) virtual, larger than the object

Exercise 3 | Q 40 | Page 241

Which of the following can make a parallel beam of light from a bulb falls on it?

(a) concave mirror as well as concave lens
(b) convex mirror as well as concave lens
(c) concave mirror as well as convex lens
(d) concave mirror as well as convex lens

Exercise 3 | Q 41 | Page 241

In order to obtain a real image twice the size of the object with a convex lens of focal length 15 cm, the object distance should be:

(a) more than 5 cm but less than 10 cm
(b) more than 10 cm but less than 15 cm
(c) more than 15 cm but less than 30 cm
(d) more than 30 cm but less than 60 cm

Exercise 3 | Q 42 | Page 242

A converging lens is used to produce an image of an object on a screen,object on a screen. What change is needed for the image to be formed nearer to the lens?

(a) increase the focal length of the lens
(b) insert a diverging lens between the lens and the screen
(c) increase the distance of the object from the lens
(d) move the object closer to the lens

Exercise 3 | Q 43 | Page 242

A convex lens of focal length 8 cm forms a real image of the same size as the object. The distance between object and its image will be:

(a) 8 cm
(b) 16 cm
(c) 24 cm
(d) 32 cm

Exercise 3 | Q 44 | Page 242

A virtual, erect and magnified image of an object is to be obtained with a convex lens. For this purpose,the object should be placed:

(a) between 2F and infinity
(b) between F and optical centre
(c) between F and 2F
(d) at F

Exercise 3 | Q 45 | Page 245

A burning candle whose flame is 1.5 cm tall is placed at a certain distance in front of a convex lens. An image of candle flame is received on a white screen kept behind the lens. The image of flame also measures 1.5 cm. If is the focal length of convex lens, the candle is placed:

(a) at f
(b) between f and 2f
(c) at 2f
(d) beyond 2f

Exercise 3 | Q 46 | Page 242

A lens of focal length 12 cm forms an erect image three times the size of the object. The distance between the object and image is:

(a) 8 cm
(b) 16 cm
(c) 24 cm
(d) 36 cm

Exercise 3 | Q 47 | Page 242

If an object is placed 21 cm from a converging lens, the image formed is slightly smaller than the object. If the object is placed 19 cm from the lens, the image formed is slightly larger than object. The approximate focal length of the lens is ______.

• 20 cm

• 18 cm

• 10 cm

• 5 cm

Exercise 3 | Q 48 | Page 242

An object is placed at the following distance from a convex lens of focal length 15 cm:

(a) 35 cm
(b) 30 cm
(c) 20 cm
(d) 10 cm
Which position of the object will produce:
(i) a magnified real image?
(ii) a magnified virtual image?
(iii) a diminished real image?
(iv) an image of same size as the object?

Exercise 3 | Q 49.1 | Page 242

When an object is placed at a distance of 36 cm from a convex lens, an image of the same size as the object is formed. What will be the nature of image formed when the object is placed at a distance of:

10 cm from the lens?

Exercise 3 | Q 49.2 | Page 242

When an object is placed at a distance of 36 cm from a convex lens, an image of the same size as the object is formed. What will be the nature of image formed when the object is placed at a distance of:

20 cm from the lens?

Exercise 3 | Q 50.1 | Page 242

Draw a diagram to show how a converging lens focusses parallel rays of light?

Exercise 3 | Q 50.2 | Page 242

How would you alter the above diagram to show how a converging lens can produce a beam of parallel rays of light.

Exercise 4 [Pages 246 - 249]

### Lakhmir Singh solutions for Class 10 Physics (Science) Chapter 5 Refraction of Light Exercise 4 [Pages 246 - 249]

Exercise 4 | Q 1 | Page 246

Write the formula for a lens connecting image distance (v), object distance (u) and the focal length (f). How does the lens formula differ from the mirror formula?

Exercise 4 | Q 2 | Page 246

Write down the magnification formula for a lens in terms of object distance and image distance. How does this magnification formula for a lens differ from the corresponding formula for a mirror?

Exercise 4 | Q 3 | Page 246

What is the nature of the image formed by a convex lens if the magnification produced by the lens is +3?

Exercise 4 | Q 4 | Page 246

What is the nature of the image formed by a convex lens if the magnification produced by the lens is, – 0.5?

Exercise 4 | Q 5 | Page 246

What is the position of image when an object is placed at a distance of 10 cm from a convex lens of focal length 10 cm?

Exercise 4 | Q 6 | Page 246

Describe the nature of image formed when an object is placed at a distance of 30 cm from a convex lens of focal length 15 cm.

Exercise 4 | Q 7 | Page 246

At what distance from a converging lens of focal length 12 cm must an object be placed in order that an image of magnification 1 will be produced?

Exercise 4 | Q 8 | Page 246

Write the new Cartesian sign convention for spherical lenses.

Exercise 4 | Q 9 | Page 246

An object 4 cm high is placed at a distance of 10 cm from a convex lens of focal length 20 cm. Find the position, nature and size of the image.

Exercise 4 | Q 10 | Page 246

A small object is so placed in front of a convex lens of 5 cm focal length that a virtual image is formed at a distance of 25 cm. Find the magnification.

Exercise 4 | Q 12 | Page 246

Calculate the focal length of a convex lens which produces a virtual image at a distance of 50 cm of an object placed 20 cm in front of it.

Exercise 4 | Q 13 | Page 246

An object is placed at a distance of 100 cm from a converging lens of focal length 40 cm.
(i) What is the nature of image?
(ii) What is the position of image?

Exercise 4 | Q 14 | Page 246

A convex lens produces an inverted image magnified three times of an object placed at a distance of 15 cm from it. Calculate focal length of the lens.

Exercise 4 | Q 15 | Page 247

A converging lens of focal length 5 cm is placed at a distance of 20 cm from a screen. How far from the lens should an object be placed so as to form its real image on the screen?

Exercise 4 | Q 16 | Page 247

An object 5 cm in length is held 25 cm away from a converging lens of focal length 10 cm. Draw the ray diagram and find the position, size and the nature of the image formed.

Exercise 4 | Q 17 | Page 247

At what distance should an object be placed from a convex lens of focal length 18 cm to obtain an image at 24 cm from it on the other side? What will be the magnification produced in this case?

Exercise 4 | Q 18 | Page 247

An object 2 cm tall is placed on the axis of a convex lens of focal length 5 cm at a distance of 10 m from the optical centre of the lens. Find the nature, position and size of the image formed. Which case of image formation by convex lenses is illustrated by this example?

Exercise 4 | Q 19 | Page 247

The filament of a lamp is 80 cm from a screen and a converging lens forms an image of it on a screen, magnified three times. Find the distance of the lens from the filament and the focal length of the lens.

Exercise 4 | Q 20 | Page 247

An erect image 2.0 cm high is formed 12 cm from a lens, the object being 0.5 cm high. Find the focal length of the lens.

Exercise 4 | Q 21 | Page 247

A convex lens of focal length 0.10 m is used to form a magnified image of an object of height 5 mm placed at a distance of 0.08 m from the lens. Calculate the position, nature and size of the image.

Exercise 4 | Q 22 | Page 247

A convex lens of focal length 6 cm is held 4 cm from a newspaper which has print 0.5 cm high. By calculation, determine the size and nature of the image produced.

Exercise 4 | Q 23 | Page 247

Determine how far an object must be placed in front of a converging lens of focal length 10 cm in order to produce an erect (upright) image of linear magnification 4.

Exercise 4 | Q 24 | Page 247

A lens of focal length 20 cm is used to produce a ten times magnified image of a film slide on a screen. How far must the slide be placed from the lens?

Exercise 4 | Q 25 | Page 247

An object placed 4 cm in front of a converging lens produces a real image 12 cm from the lens.
(a) What is the magnification of the image?
(b) What is the focal length of the lens?
(c) Draw a ray diagram to show the formation of image. Mark clearly F and 2F in the diagram.

Exercise 4 | Q 26 | Page 247

An object 2 cm tall stands on the principal axis of a converging lens of focal length 8 cm. Find the position, nature and size of the image formed if the object is:
(i) 12 cm from the lens
(ii) 6 cm from the lens
State one practical application each of the use of such a lens with the object in position (i) and (ii).

Exercise 4 | Q 27.1 | Page 247

An object 3 cm high is placed 24 cm away from a convex lens of focal length 8 cm. Find by calculations, the position, height and nature of the image.

Exercise 4 | Q 27.2 | Page 247

If the object is moved to a point only 3 cm away from the lens, what is the new position, height and nature of the image?

Exercise 4 | Q 27.3 | Page 247

Which of the above two cases illustrates the working of a magnifying glass?

Exercise 4 | Q 28.1 | Page 247

Find the nature, position and magnification of the images formed by a convex lens of focal length 0.20 m if the object is placed at a distance of:

0.50 m

Exercise 4 | Q 28.2 | Page 247

Find the nature, position and magnification of the images formed by a convex lens of focal length 0.20 m if the object is placed at a distance of:

0.25 m

Exercise 4 | Q 28.3 | Page 247

Find the nature, position and magnification of the images formed by a convex lens of focal length 0.20 m if the object is placed at a distance of:

0.15 m

Exercise 4 | Q 29 | Page 247

A spherical mirror and a thin spherical lens have each a focal length of -15 cm. The mirror and the lens are likely to be

• both concave

• both convex

• the mirror is concave and the lens is convex

• the mirror is convex, but the lens is concave

Exercise 4 | Q 30 | Page 247

Linear magnification produced by a convex lens can be:
(a) less than 1 or more than 1
(b) less than 1 or equal to 1
(c) more than 1 or equal to 1
(d) less than 1, equal to 1 or more than 1

Exercise 4 | Q 31 | Page 248

Magnification produced by a concave lens is always:
(a) more than 1
(b) equal to 1
(c) less than 1
(d) more than 1 or less than 1

Exercise 4 | Q 32 | Page 248

In order to obtain a magnification of, –3 (minus 3) with a convex lens, the object should be placed:
(a) between optical centre and F
(b) between F and 2F
(c) at 2F
(d) beyond 2F

Exercise 4 | Q 33 | Page 248

A convex lens produces a magnification of + 5. The object is placed:
(a) at focus
(b) between f and 2f
(c) at less than f
(d) beyond 2

Exercise 4 | Q 34 | Page 248

If a magnification of, –1 (minus 1) is obtained by using a converging lens, then the object has to be placed:
(a) within f
(b) at 2f
(c) beyond 2f
(d) at infinity

Exercise 4 | Q 35 | Page 248

To obtain a magnification of, –0.5  with a convex lens, the object should be placed:
(a) at F
(b) between optical centre and F
(c) between F and 2F
(d) beyond 2F

Exercise 4 | Q 36 | Page 248

An object is 0.09 m from a magnifying lens and the image is formed 36 cm from the lens. The magnification produced is:
(a) 0.4
(b) 1.4
(c) 4.0
(d) 4.5

Exercise 4 | Q 37 | Page 248

To obtain a magnification of, –2 with a convex lens of focal length 10 cm, the object should be placed:
(a) between 5 cm and 10 cm
(b) between 10 cm and 20 cm
(c) at 20 cm
(d) beyond 20 cm

Exercise 4 | Q 38 | Page 248

A convex lens of focal length 15 cm produces a magnification of +4. The object is placed:
(a) at a distance of 15 cm
(b) between 15 cm and 30 cm
(c) at less than 15 cm
(d) beyond 30 cm

Exercise 4 | Q 39 | Page 248

If a magnification of, –1 is to be obtained by using a converging lens of focal length 12 cm, then the object must be placed:
(a) within 12 cm
(b) at 24 cm
(c) at 6 cm
(d) beyond 24 cm

Exercise 4 | Q 40 | Page 248

In order to obtain a magnification of, –0.75 with a convex lens of focal length 8 cm, the object should be placed:
(a) at less than 8 cm
(b) between 8 cm and 16 cm
(c) beyond 16 cm
(d) at 16 cma

Exercise 4 | Q 41.1 | Page 248

A student did an experiment with a convex lens. He put an object at different distances 25 cm, 30 cm, 40 cm, 60 cm and 120 cm from the lens. In each case he measured the distance of the image from the lens. His results were 100 cm, 24 cm, 60 cm, 30 cm and 40 cm, respectively. Unfortunately his results are written in wrong order.

Rewrite the image distances in the correct order.

Exercise 4 | Q 41.2 | Page 248

A student did an experiment with a convex lens. He put an object at different distances 25 cm, 30 cm, 40 cm, 60 cm and 120 cm from the lens. In each case he measured the distance of the image from the lens. His results were 100 cm, 24 cm, 60 cm, 30 cm and 40 cm, respectively. Unfortunately his results are written in wrong order.

What would be the image distance if the object distance was 90 cm?

Exercise 4 | Q 41.3 | Page 248

A student did an experiment with a convex lens. He put an object at different distances 25 cm, 30 cm, 40 cm, 60 cm and 120 cm from the lens. In each case he measured the distance of the image from the lens. His results were 100 cm, 24 cm, 60 cm, 30 cm and 40 cm, respectively. Unfortunately his results are written in wrong order.

Which of the object distances gives the biggest image?

Exercise 4 | Q 41.4 | Page 248

A student did an experiment with a convex lens. He put an object at different distances 25 cm, 30 cm, 40 cm, 60 cm and 120 cm from the lens. In each case he measured the distance of the image from the lens. His results were 100 cm, 24 cm, 60 cm, 30 cm and 40 cm, respectively. Unfortunately his results are written in wrong order.

What is the focal length of this lens?

Exercise 4 | Q 42.1 | Page 248

A magnifying lens has a focal length of 100 mm. An object whose size is 16 mm is placed at some distance from the lens so that an image is formed at a distance of 25 cm in front of the lens.

What is the distance between the object and the lens?

Exercise 4 | Q 42.2 | Page 248

A magnifying lens has a focal length of 100 mm. An object whose size is 16 mm is placed at some distance from the lens so that an image is formed at a distance of 25 cm in front of the lens.

Where should the object be placed if the image is to form at infinity?

Exercise 4 | Q 43 | Page 248

A lens forms a real image 3 cm high of an object 1 cm high. If the separation of object and image is 15 cm, find the focal length of the lens.

Exercise 4 | Q 44 | Page 249

An object 50 cm tall is placed on the principal axis of a convex lens. Its 20 cm tall image is formed on the screen placed at a distance of 10 cm from the lens. Calculate the focal length of the lens.

Exercise 5 [Pages 251 - 253]

### Lakhmir Singh solutions for Class 10 Physics (Science) Chapter 5 Refraction of Light Exercise 5 [Pages 251 - 253]

Exercise 5 | Q 1 | Page 251

If the image formed by a lens is always diminished and erect, what is the nature of the lens?

Exercise 5 | Q 2 | Page 255

A 50 cm tall object is at a very large distance from a diverging lens. A virtual, erect and diminished image of the object is formed at a distance of 20 cm in front of the lens. How much is the focal length of the lens?

Exercise 5 | Q 2 | Page 251

Copy and complete the diagram below to show what happens to the rays of light when they pass through the concave lens:

Exercise 5 | Q 3.1 | Page 252

Which type of lenses are:

thinner in the middle than at the edges?

Exercise 5 | Q 3.2 | Page 252

Which type of lenses are:

thicker in the middle than at the edges?

Exercise 5 | Q 4 | Page 252

A ray of light is going towards the focus of a concave lens. draw a ray diagram to show the path of this ray of light after refraction through the lens.

Exercise 5 | Q 5 | Page 252

What type of image is always made by a concave lens?

Exercise 5 | Q 5.1 | Page 252

What type of images can a convex lens make?

Exercise 5 | Q 5.2 | Page 252

What type of image is always made by a concave lens?

Exercise 5 | Q 6 | Page 252

Take down this figure into your answer book and complete the path of the ray.

Exercise 5 | Q 7.1 | Page 252

Fill in the following blank with suitable word:

A convex lens .................. rays of light, whereas a concave lens .................. rays of light.

Exercise 5 | Q 7.2 | Page 252

Fill in the following blank with suitable word:

Lenses refract light to form images: a..................... lens can form both real and virtual images, but a diverging lens forms only ...................... images.

Exercise 5 | Q 8 | Page 252

Things always look small on viewing through a lens. What is the nature of the lens?

Exercise 5 | Q 9 | Page 252

An object lies at a distance of 2f from a concave lens of focal length f. Draw a ray-diagram to illustrate the image formation.

Exercise 5 | Q 10 | Page 252

Show by drawing a ray-diagram that the image of an object formed by a concave lens is virtual, erect and diminished.

Exercise 5 | Q 11.1 | Page 252

Give the position, size and nature of image of formed by a concave lens when the object is placed:
anywhere between optical centre and infinity.

Exercise 5 | Q 11.2 | Page 252

Give the position, size and nature of image of formed by a concave lens when the object is placed:

at infinity.

Exercise 5 | Q 12.1 | Page 252

Which type of lens is :

a converging lens, and which is

Exercise 5 | Q 12.2 | Page 252

Which type of lens is

Exercise 5 | Q 13 | Page 252

With the help of a diagram, explain why the image of an object viewed through a concave lens appears smaller and closer than the object.

Exercise 5 | Q 14.1 | Page 252

How would a pencil look like if you saw it through

a concave lens  Is the image real or virtual?

Exercise 5 | Q 14.2 | Page 252

How would a pencil look like if you saw it through How would a pencil look like if you saw it through

Exercise 5 | Q 15.1 | Page 252

An object is placed 10 cm from a lens of focal length 5 cm. Draw the ray diagrams to show the formation of image if the lens is  converging,

Exercise 5 | Q 15.2 | Page 252

An object is placed 10 cm from a lens of focal length 5 cm. Draw the ray diagrams to show the formation of image if the lens is  diverging.

Exercise 5 | Q 15.3 | Page 252

State one practical use each of convex mirror, concave mirror, convex lens and concave lens.

Exercise 5 | Q 16.1 | Page 252

Construct ray diagrams to illustrate the formation of a virtual image using  a converging lens,

Exercise 5 | Q 16.2 | Page 252

Construct ray diagrams to illustrate the formation of a virtual image using   a diverging lens.

Exercise 5 | Q 16.3 | Page 252

What is the difference between the two images formed above?

Exercise 5 | Q 17 | Page 252

A diverging lens is used in:
(a) a magnifying glass
(b) a car to see objects on rear side
(c) spectacles for the correction of short sight
(d) a simple camera

Exercise 5 | Q 18 | Page 252

When an object is kept at any distance in front of a concave lens, the image formed is always:
(a) virtual, erect and magnified
(b) virtual, inverted and diminished.
(c) virtual, erect and diminished
(d) virtual, erect and same size as object

Exercise 5 | Q 19 | Page 252

When sunlight is concentrated on a piece of paper by a spherical mirror or lens, then a hole can be burnt in it. For doing this, the paper must be placed at he focus of:
(a) either a convex mirror or convex lens
(b) either a concave mirror or concave lens
(c) either a concave mirror or convex lens
(d) either a convex mirror or concave lens

Exercise 5 | Q 20 | Page 253

A beam of parallel light rays is incident through the holes on one side of a box and emerges out through the holes on its opposite side as shown in the diagram below:

Which of the following could be inside the box?
(a) a rectangular glass block
(b) a concave lens
(c) a convex lens
(d) a glass prism

Exercise 5 | Q 21 | Page 253

A beam of light is incident through the holes on one side of a box and emerges out through the holes on its opposite side as shown in the following figure:

The box contains:
(a) a glass prism
(b) a concave lens
(c) a convex lens
(d) a parallel-sided glass slab

Exercise 5 | Q 22 | Page 253

Which of the following can form a virtual image which is always smaller than the object?
(a) a plane mirror
(b) a convex lens
(c) a concave lens
(d) a concave mirror

Exercise 5 | Q 22 | Page 253

Which of the following can form a virtual image which is always smaller than the object?
(a) a plane mirror
(b) a convex lens
(c) a concave lens
(d) a concave mirror

Exercise 5 | Q 23 | Page 253

When an object is placed 10 cm in front of lens A, the image is real, inverted, magnified and formed at a great distance. When the same object is placed 10 cm in front of lens B, the image formed is real, inverted and same size as the object.

What is the nature of lens A?

Exercise 5 | Q 23.1 | Page 253

When an object is placed 10 cm in front of lens A, the image is real, inverted, magnified and formed at a great distance. When the same object is placed 10 cm in front of lens B, the image formed is real, inverted and same size as the object.

What is the focal length of lens A?

Exercise 5 | Q 23.2 | Page 253

When an object is placed 10 cm in front of lens A, the image is real, inverted, magnified and formed at a great distance. When the same object is placed 10 cm in front of lens B, the image formed is real, inverted and same size as the object.

What is the focal length of lens B?

Exercise 5 | Q 23.4 | Page 253

When an object is placed 10 cm in front of lens A, the image is real, inverted, magnified and formed at a great distance. When the same object is placed 10 cm in front of lens B, the image formed is real, inverted and same size as the object.

What is the nature of lens B?

Exercise 5 | Q 24 | Page 253

When a fork is seen through lenses A and B one by one, it appears as shown in the diagrams. What is the nature of (i) lens A, and (ii) lens B? Give reason for your answer.

Exercise 5 | Q 25.1 | Page 253

What kind of lens can form:

an inverted magnified image?

Exercise 5 | Q 25.2 | Page 253

What kind of lens can form:

an erect magnified image?

Exercise 5 | Q 25.3 | Page 253

What kind of lens can form:

an inverted diminished image?

Exercise 5 | Q 25.4 | Page 253

What kind of lens can form:

am erect diminished image?

Exercise 6 [Pages 255 - 257]

### Lakhmir Singh solutions for Class 10 Physics (Science) Chapter 5 Refraction of Light Exercise 6 [Pages 255 - 257]

Exercise 6 | Q 1.1 | Page 255

The lens A produces a magnification of, − 0.6 whereas lens B produces a magnification of + 0.6.

What is the nature of lens A?

Exercise 6 | Q 1.2 | Page 255

The lens A produces a magnification of, − 0.6 whereas lens B produces a magnification of + 0.6.

What is the nature of lens B

Exercise 6 | Q 3 | Page 256

An object is placed at a distance of 4 cm from a concave lens of focal length 12 cm. Fine the position and nature of the image.

Exercise 6 | Q 4 | Page 256

A concave lens of focal length 15 cm forms an image 10 cm from the lens. How far is the object placed from the lens? Draw the ray-diagram.

Exercise 6 | Q 5 | Page 256

An object 60 cm from a lens gives a virtual image at a distance of 20 cm in front of the lens. What is the focal length of the lens? Is the lens converging or diverging? Give reasons for your answer.

Exercise 6 | Q 6 | Page 256

A concave lens of 20 cm focal length forms an image 15 cm from the lens. Compute the object distance.

Exercise 6 | Q 7 | Page 256

A concave lens has focal length 15 cm. At what distance should the object from the lens be placed so that it forms an image at 10 cm from the lens? Also find the magnification produced by the lens.

Exercise 6 | Q 8 | Page 256

Calculate the image distance for an object of height 12 mm at a distance of 0.20 m from a concave lens of focal length 0.30 m, and state the nature and size of the image.

Exercise 6 | Q 10 | Page 256

An object is placed 20 cm from (a) a converging lens, and (b) a diverging lens, of focal length 15 cm. Calculate the image position and magnification in each case.

Exercise 6 | Q 11 | Page 256

A 2.0 cm tall object is placed 40 cm from a diverging lens of focal length 15 cm. Find the position and size of the image.

Exercise 6 | Q 12 | Page 256

(a) Find the position and size of the virtual image formed when an object 2 cm tall is placed 20 cm from:
(i) a diverging lens of focal length 40 cm.
(ii) a converging lens of focal length 40 cm.
(b) Draw labelled ray diagrams to show the formation of images in case (i) and (ii) above (The diagrams may not be according to scale).

Exercise 6 | Q 13.1 | Page 256

A small object is placed 150 mm away from a diverging lens of focal length 100 mm.
(i) Copy the figure below and draw rays to show how an image is formed by the lens.
Figure
(ii) Calculate the distance of the image from the lens by using the lens formula.

Exercise 6 | Q 13.2 | Page 256

The diverging lens in part (a) is replaced by a converging lens also of focal length 100 mm. The object remains in the same position and an image is formed by the converging lens. Compare two properties of this image with those of the image formed by the diverging lens in part (a).

Exercise 6 | Q 14 | Page 256

A concave lens produces an image 20 cm from the lens of an object placed 30 cm from the lens. The focal length of the lens is:
(a) 50 cm
(b) 40 cm
(c) 60 cm
(d) 30 cm

Exercise 6 | Q 15 | Page 256

Only one of the following applies to a concave lens. This is:
(a) focal length is positive
(b) image distance can be positive or negative
(c) height of image can be positive or negative
(d) image distance is always negative

Exercise 6 | Q 16 | Page 256

The magnification produced by a spherical mirror and a spherical lens is + 0.8.
(a) The mirror and lens are both convex
(b) The mirror and lens are both concave
(c) The mirror is concave but the lens is convex
(d) The mirror is convex but the lens is concave

Exercise 6 | Q 17 | Page 256

The magnification produced by a spherical lens and a spherical mirror is + 2.0.
(a) The lens and mirror are both concave
(b) The lens and mirror are both convex
(c) The lens is convex but the mirror is concave
(d) The lens is concave but the mirror is convex

Exercise 6 | Q 18.1 | Page 257

A camera fitted with a lens of focal length 50 mm is being used to photograph a flower that is 5 cm in diameter. The flower is placed 20 cm in front of the camera lens.

At what distance from the film should the lens be adjusted to obtain a sharp image of the flower?

Exercise 6 | Q 18.2 | Page 257

What would be the diameter of the image of the flower on the film?

Exercise 6 | Q 19 | Page 256

An object is 2 m from a lens which forms an erect image one-fourth (exactly) the size of the object. Determine the focal length of the lens. What type of lens is this?

Exercise 6 | Q 20.1 | Page 257

An image formed on a screen is three times the size of the object. The object and screen are 80 cm apart when the image is sharply focussed.

State which type of lens is used.

Exercise 6 | Q 20.2 | Page 257

An image formed on a screen is three times the size of the object. The object and screen are 80 cm apart when the image is sharply focussed.

Calculate focal length of the lens.

Exercise 7 [Pages 261 - 263]

### Lakhmir Singh solutions for Class 10 Physics (Science) Chapter 5 Refraction of Light Exercise 7 [Pages 261 - 263]

Exercise 7 | Q 1 | Page 261

The lens A has a focal length of 25 cm whereas another lens B has a focal length of 60 cm. Giving reason state, which lens has more power: A or B.

Exercise 7 | Q 2 | Page 261

Which causes more bending (or more refraction) of light rays passing through it : a convex lens of long focal length or a convex lens of short focal length?

Exercise 7 | Q 3 | Page 261

Name the physical quantity whose unit is dioptre.

Exercise 7 | Q 4 | Page 261

Define 1 dioptre of power of a lens.

Exercise 7 | Q 5 | Page 261

Which type of lens has (a) a positive power, and (b) a negative power?

Exercise 7 | Q 6 | Page 261

Which of the two has a greater power: a lens of short focal length or a lens of large focal length?

Exercise 7 | Q 7 | Page 261

How is the power of a lens related to its focal length?

Exercise 7 | Q 8 | Page 261

Which has more power : a thick convex lens or a thin convex lens, made of the same glass? Give reason for your choice.

Exercise 7 | Q 9 | Page 261

The focal length of a convex lens is 25 cm. What is its power?

Exercise 7 | Q 10 | Page 261

What is the power of a convex lens of focal length 0.5 m?

Exercise 7 | Q 11 | Page 261

A converging lens has focal length of 50 mm. What is the power of the lens?

Exercise 7 | Q 12 | Page 261

What is the power of a convex lens lens whose focal length is 80 cm?

Exercise 7 | Q 13 | Page 261

A diverging lens has focal length of 3 cm. Calculate the power.

Exercise 7 | Q 14 | Page 261

The power of a lens is + 0.2 D. Calculate its focal length.

Exercise 7 | Q 15 | Page 261

The power of a lens is, −2 D. What is its focal length?

Exercise 7 | Q 16 | Page 261

What is the nature of a lens having a power of + 0.5 D?

Exercise 7 | Q 17 | Page 261

What is the nature of a lens whose power is, −4 D?

Exercise 7 | Q 18 | Page 261

The optician's prescription for a spectacle lens is marked +0.5 D. What is the:
(a) nature of spectacle lens?
(b) focal length of spectacle lens?

Exercise 7 | Q 19 | Page 261

A doctor has prescribed a corrective lens of power, −1.5 D. Find the focal length of the lens. Is the prescribed lens diverging or converging?

Exercise 7 | Q 20 | Page 262

A lens has a focal length of, −10 cm. What is the power of the lens and what is its nature?

Exercise 7 | Q 21 | Page 262

The focal length of a lens is +150 mm. What kind of lens is it and what is its power?

Exercise 7 | Q 22.1 | Page 262

Fill in the following blank with suitable words :

The reciprocal of the focal length in metres gives you the _________ of the lens, which is measured in ___________.

Exercise 7 | Q 22.2 | Page 262

Fill in the following blank with suitable word:

For converging lenses, the power is __________ while for diverging lenses, the power is ___________.

Exercise 7 | Q 23 | Page 262

An object of height 4 cm is placed at a distance of 15 cm in front of a concave lens of power, −10 dioptres. Find the size of the image.

Exercise 7 | Q 24 | Page 262

An object of height 4.25 mm is placed at a distance of 10 cm from a convex lens of power +5D. Find (i) the focal length of the lens, and (ii) the size of the image.

Exercise 7 | Q 25 | Page 262

A convex lens of power 5 D and a concave lens of power 7.5 D are placed in contact with each other. What is the :
(a) power of this combination of lenses?
(b) focal length of this combination of lenses?

Exercise 7 | Q 26 | Page 262

A convex lens of focal length 25 cm and a concave lens of focal length 10 cm are placed in close contact with one another.
(a) What is the power of this combination?
(b) What is the focal length of this combination?
(c) Is this combination converging or diverging?

Exercise 7 | Q 27 | Page 262

The power of a combination of two lenses X and Y is 5 D. If the focal length of lens X be 15 cm :
(a) calculate the focal length of lens Y.
(b) state the nature of lens Y.

Exercise 7 | Q 28 | Page 262

Two lenses A and B have focal lengths of +20 cm and, −10 cm, respectively.
(a) What is the nature of lens A and lens B?
(b) What is the power of lens A and lens B?
(c) What is the power of combination if lenses A and B are held close together?

Exercise 7 | Q 29.1 | Page 262

What do you understand by the power of a lens? Name one factor on which the power of a lens depends.

Exercise 7 | Q 29.2 | Page 262

What is the unit of power of a lens? Define the unit of power of a lens.

Exercise 7 | Q 29.3 | Page 262

A combination of lenses for a camera contains two converging lenses of focal lengths 20 cm and 40 cm and a diverging lens of focal length 50 cm. Find the power and focal length of the combination.A optical instrument in which the above arrangement of convex lens is used is a convex lens used to burn paper by focusing sunlight.

Exercise 7 | Q 30.1 | Page 262

Two lenses A and B have power of (i) +2D and (ii) −4D respectively. What is the nature and focal length of each lens?

Exercise 7 | Q 30.2 | Page 262

An object is placed at a distance of 100 cm from each of the above lenses A and B. Calculate (i) image distance, and (ii) magnification, in each of the two cases.

Exercise 7 | Q 31 | Page 262

The focal lengths of four convex lenses PQR and S are 20 cm, 15 cm, 5 cm and 10 cm, respectively. The lens having greatest power is :
(a) P
(b) Q
(c) R
(d) S

Exercise 7 | Q 32 | Page 262

A converging lens has a focal length of 50 cm. The power of this lens is:

• +0.2D

• −2.0D

• +2.0D

• −0.2D

Exercise 7 | Q 33 | Page 262

A diverging lens has a focal length of 0.10 m. The power of this lens will be:

• +10.0D

• +1.0D

• −1.0D

• −10.0D

Exercise 7 | Q 34 | Page 262

The power of a lens is +2.0D. Its focal length should be :

• 100 cm

• 50 cm

• 25 cm

• 40 cm

Exercise 7 | Q 35 | Page 262

If a spherical lens has a power of, −0.25 D, the focal length of this lens will be :
(a) −4 cm
(b) −400 mm
(c) −4 m
(d) −40 cm

Exercise 7 | Q 35 | Page 262

If a spherical lens has a power of, −0.25 D, the focal length of this lens will be :
(a) −4 cm
(b) −400 mm
(c) −4 m
(d) −40 cm

Exercise 7 | Q 36 | Page 263

The power of a concave lens is 10 D and that of a convex lens is 6 D. When these two lenses are placed in contact with each other, the power of their combination will be :
(a) +16 D
(b) +4 D
(c) −16 D
(d) −4 D

Exercise 7 | Q 37 | Page 263

The power of a converging lens is 4.5 D and that of a diverging lens is 3 D. The power of this combination of lenses placed close together is :
(a) +1.5D
(b) +7.5D
(c) −7.5D
(d) −1.5D

Exercise 7 | Q 38 | Page 263

A convex lens of focal length 10 cm is placed in contact with a concave lens of focal length 20 cm. The focal length of this combination of lenses will be:
(a) +10 cm
(b) +20 cm
(c) −10 cm
(d) −20 cm

Exercise 7 | Q 39.1 | Page 263

The optical prescription for a pair of spectacles is :
Right eye : −3.50 D
Left eye : −4.00 D

Are these lenses thinner at the middle or at the edges?

Exercise 7 | Q 39.2 | Page 263

The optical prescription for a pair of spectacles is :
Right eye : −3.50 D
Left eye : −4.00 D

Which lens has a greater focal length?

Exercise 7 | Q 39.3 | Page 263

The optical prescription for a pair of spectacles is :
Right eye : −3.50 D
Left eye : −4.00 D

Which is the weaker eye?

Exercise 7 | Q 40.1 | Page 263

A person got his eyes tested by an optician. The prescription for the spectacle lenses to be made reads :
Left eye : +2.50 D
Right eye : +2.00 D

State whether these lenses are thicker in the middle or at the edges.

Exercise 7 | Q 40.2 | Page 263

A person got his eyes tested by an optician. The prescription for the spectacle lenses to be made reads :
Left eye : +2.50 D
Right eye : +2.00 D

Which lens bends the light rays more strongly?

Exercise 7 | Q 40.3 | Page 263

A person got his eyes tested by an optician. The prescription for the spectacle lenses to be made reads :
Left eye : +2.50 D
Right eye : +2.00 D

State whether these spectacle lenses will converge light rays or diverge light rays.

## Solutions for Chapter 5: Refraction of Light

Exercise 1Exercise 2Exercise 3Exercise 4Exercise 5Exercise 6Exercise 7 ## Lakhmir Singh solutions for Class 10 Physics (Science) chapter 5 - Refraction of Light

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Concepts covered in Class 10 Physics (Science) chapter 5 Refraction of Light are Spherical Mirrors, Concave Mirror, Convex Mirror, Concave Lens, Refraction of Light, Image Formation by Convex Mirror, Sign Convention for Reflection by Spherical Mirrors, Mirror Equation/Formula, Images Formed by Spherical Mirrors, Image Formation by Concave Mirror, Reflection of Light, Law of Reflection of Light, Linear Magnification (M) Due to Spherical Mirrors, Magnification Due to Spherical Lenses, Power of a Lens, Mirrors and Its Types, Plane Mirror and Reflection, Rules for the Construction of Image Formed by a Spherical Mirror, Refraction of Light Through a Rectangular Glass Slab, Law of Refraction of Light, Refractive Index, Spherical Lens, Images Formed by Sperical Lenses, Guideline for Image Formation Due to Refraction Through a Convex and Concave Lens, Images Formed Due to Refraction Through a Concave Lens, Convex Lens, Images Formed Due to Refraction Through a Convex Lens, Sign Convention for Spherical Lenses, Lens Formula.

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