Reflection of Light Selina 9th Concise Physics Solutions

Reflection of Light Selina 9th Concise Physics Solutions  Chapter-7 Reflection of Light .Step By Step Revised Concise Selina Physics Solutions of Chapter-7 Reflection of Light with Exe-7(A) , MCQ 7(A),Num 7(A) Exe-7(B) ,  MCQ -7(B) Num 7(B), Exe-7(C),  MCQ-7(C), Num 7(C)for Class-9.  Visit official Website CISCE for detail information about ICSE Board Class-9.

Board ICSE
Publications Selina Publication
Subject Physics
Class 9th
Chapter-7 Reflection of Light Exe-7(A)
Book Name Concise
Topics Solution of Exercise-7(A),  MCQ-7(A),  Num-7(A),    Exercise-7(A),  MCQ-7(A),  Num-7(A)   and  Exercise-7(A),  MCQ-7(A),  Num-7(A)
Academic Session 2021-2022

Reflection of Light Selina Concise Physics Solutions Class 9th


–: Select Topics :–

Exercise-7(A),  MCQ-7(A),  Num-7(A)

Exercise-7(B),  MCQ-7(B),  Num-7(B)

Exercise-7(C),  MCQ-7(C),  Num-7(C)

Note :-  Before Viewing Selina Concise Physics Solutions of Chapter-7 Reflection of Light for ICSE Class-9 Physics. Read the whole chapter carefully and Solved all example of Chapter-7 Reflection of Light for Class-9 Physics.

 Latest syllabus of council for class 9th physics, Law of reflection, character of image, Spherical Mirror, Ray diagram and use of spherical mirror, Type of mirror, radius of curvature, Pole, Principal Axis, Focus and Focal Length.


Exe-7(A) Reflection of Light Selina Concise 9th physics solutions

Question 1

What do you mean by reflection of light?

Answer 1

The return of light into the same medium after striking a surface is called reflection.

Question 2

State which surface of a plane mirror reflects most of the light incident on it: the front smooth surface or the back silvered surface.

Answer 2

Black silvered surface reflects most of the light incident on it.

Question 3

Explain the following terms:

(a) Plane mirror,  (b) Incident ray,

(c) Reflected ray,  (d) Angle of incidence and

(e) Angle of reflection.

Draw diagram/diagrams to show them.

Answer 3

(a) Plane mirror: Plane mirror is a highly polished and smooth reflecting surface made from a clear plane glass sheet, usually thin and silvered with suitable reflecting abrasive (for example, mercury) on one side. Once this pasting is done, then the glass becomes opaque but due to the reflecting property of the abrasive, the plane glass sheet becomes a plane glass reflector or a plane glass mirror.

plane miror

(b) Incident ray: The light ray striking a reflecting surface is called the incident ray.

(c) Reflected ray: The light ray obtained after reflection from the surface, in the same medium in which the incident ray is travelling, is called the reflected ray.

(d) Angle of incidence: The angle which the incident ray makes with the normal at the point of incidence is called the angle of incidence. It is denoted by the letter i.

(e) Angle of reflection: The angle which the reflected ray makes with the normal at the point of incidence is called the angle of reflection. It is denoted by the letter r.

angle of reflection

Question 4

With the help of diagrams, explain the difference between the regular and irregular reflection.

Answer 4

regular and irregular reflection

Regular reflection occurs when a beam of light falls on a smooth and polished surface and irregular reflection occurs when a beam of light falls on a rough surface. Since the surface is uneven, from different points light rays get reflected in different directions and give rise to irregular reflection.

Question 5

Differentiate between the reflection of light from a plane mirror and that from a plane sheet of paper.

Answer 5

Reflection of light from a plane mirror is regular reflection and reflection of light from plane sheet of paper is irregular reflection of light.

Question 6

State the two laws of reflection of light.

Answer 6

Laws of reflection:

  1. The angle of incidence is equal to the angle of reflection.
  2. The incident ray, the reflected ray and the normal at the point of incidence, lie in the same plane

Question 7

State the law of reflection and describe an experiment to verify them.

Answer 7

law of reflection 6

law of reflection 2

Question 8

A light ray is incident normally on a plane mirror. (a) What is its angle of incidence?

(b) What is the direction of reflected ray? Show it on a diagram.

Answer 8

(a) 0o

(b) Same as the incident ray

incident ray

Question 9

Draw a diagram to show the reflection of a ray of light using a plane mirror. In the diagram, label the incident ray, the reflected ray, the normal, the angle of incidence and the angle of reflection.

Answer 9

reflection of light in pkane mirror

Question 10

Fig. 7.15 shows an incident ray AO and the normal ON on a plane mirror. The angle which the incident ray AO makes with mirror is 30 . (a) Find the angle of incidence. (b) Draw the reflected ray and then find the angle between the incident and reflected rays.

incident ray on a plane mirror

Answer 10

(a) Angle of incidence = 90– 30o = 60o

(b) Angle between the incident ray and reflected ray = Angle of incidence + Angle of reflection

Angle of reflection = Angle of incidence = 60o

Therefore, Angle between the incident ray and reflected ray = 60o + 60o = 120o

angle between incident ray and reflected ray

Question 11

The diagram in Fig. 7.16 shows a point object in front of a plane mirror MM1.

(a) Complete the diagram by taking two rays from the point to show the formation of its image.

2 rays diagram

(b) In the diagram, mark the position of eye to see the image.

(c) Is the image formed real or virtual? Explain why?

Answer 11

(a) and (b)

ray diagram 1,2

(c) The image formed is virtual because the reflected rays meet when produced backwards.

Question 12

The diagram below in Fig7.17. shows an object XY in front of a plane mirror. Draw on the diagram, the image of the object formed by the mirror. Trace the path of two rays from a point on the object to show the formation of image.

plane mirror 2

Answer 12

plane mirror 3

Question 13

  1. a) Write three characteristics of the image formed by a plane mirror?

(b) How is the position of an image related to the position of the object?

Answer 13

(a) Three characteristics of image formed by plane mirror:

(i) Image formed in erect (upright)

(ii) Image formed is virtual

(iii) Image formed is of the same size as the object

(b) The image is situated at the same perpendicular distance behind the mirror as the object in front of it.

Question 14

Differentiate between a real and a virtual image.

Answer 14

Real Image Virtual image
1. A real image is formed due to actual intersection of the reflected rays. 1. A virtual image is formed when the reflected rays meet if they are produced backwards.
2. A real image can be obtained on a screen. 2. A virtual image cannot 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 15

What is meant by lateral inversion of an image in a plane mirror? Explain it with the help of a ray diagram.

Answer 15

The interchange of the left and right sides in the image of an object in a plane mirror is called lateral inversion.

letreal inversion

Figure above shows the image formation of a letter P in a plane mirror. The letter P appears in the plane mirror as .

Question 16

The letters on the front of an ambulance are written laterally inverted like . Give reason.

Answer 16

The letters on the front of a ambulance are written laterally inverted, so that the driver of the vehicle moving ahead of the ambulance reads these words laterally inverted as AMBULANCE, in his rear view mirror, and gices side to pass the ambulance first.

Question 17

Why is it difficult to read the image of the text of a page formed due to reflection by a plane mirror?

Answer 17

Due to lateral inversion, , it becomes difficult to read the image of the text of a page formed due to reflection by a plane mirror.


MCQ-7(A) Reflection of Light Selina  Concise physics solutions

Question 1

According to the law of reflection:

(a) i/r = constant

(b) sin i /sin r = constant

(c) = constant

(d) r

Answer 1

r

Question 2

The image formed by a plane mirror has the following characteristic:

(a) Erect and diminished

(b) Erect and enlarged

(c) Inverted and of same size

(d) Erect and of same size.

Answer 2

Erect and of same size

Question 3

The image formed by a plane mirror is :

(a) real

(b) virtual

(c) virtual with lateral inversion

(d) real with lateral inversion

Answer 3

virtual with lateral inversion


NUM-7(A) Reflection of Light Selina Concise  physics solutions

Question 1

The  ray  is incident on a plane mirror. Its reflected ray is perpendicular to the incident ray.  Find the angle of incidence.

Answer 1

Angle of incidence (i) + Angle of reflection(r) = 90

But, as per the laws of reflection, i = r

Therefore, 2 i = 90o

Or, i = r = 45o

Question 2

A man standing in front of a plane mirror finds his image at a distance 6 metre from himself. What is the distance of man from the mirror?

Answer 2

Distance between man and his image = 6m

Distance between man and mirror + distance between mirror and image = 6m

But, Distance between man and mirror (object distance) = distance between mirror and image (image distance)

Therefore, distance of man from mirror = 6/2 = 3m

Question 3

An insect is sitting in front of a plane mirror at a distance 1 m from it.

(a) Where is the image of the insect formed? (b) What is the distance between the insect and its image?

Answer 3

(a) Image of the insect is formed 1m behind the mirror.

(b) Distance between the insect and his image = 1 + 1 = 2 m

Question 4

An object is kept at 60 cm in front of a plane mirror. If the mirror is now moved 25 cm away from the object, how does the image shift from its previous position?

Answer 4

Initially, distance of the object from the mirror = 60 cm.

Therefore, image is formed at a distance 60 cm from the mirror, behind it.

Thus, initial distance between the object and image = 60 + 60 = 120 cm

If the mirror is moved 25 cm away from the object,

The new distance of the object from the mirror = 60 + 25 = 85 cm

The new image is now at a distance 85 cm from the mirror behind it.

Thus, new distance of the image from the object = 85 + 85 = 170 cm

Taking the position of the object as reference point, the distance between the two positions of the image = new distance of image from the object – initial distance of the image from the object

 = (170 – 120) cm = 50 cm

Thus, the image shifts 50 cm away.

Question 5

An optician while testing the eyes of a patient keeps a chart of letters 3 m behind the patient and asks him to see the letters on the image of chart formed in a plane mirror kept at distance 2 m in front of him. How far away is the chart seen by the patient?

Answer 5

Distance between man and chart = 3m

Distance between man and mirror = 2m

Therefore, distance between chart and mirror = 5 m

Now, final image is formed on the mirror, which is at a distance of 2 m from the man, therefore, the chart as seen by patient is (5m + 2m =) 7m away.


EXE-7(B) Reflection of Light Selina Revised Concise 9th physics solution

Question 1

Two plane mirrors are placed making an angle in between them. Write an expression for the number of images formed of an object placed in between the mirrors. State the condition, if any.

Answer 1

If two mirrors make an angle  with each other and object is placed in between the two mirrors, the number of images formed is n or (n – 1) depending upon n = 360o /   o is odd or even.

(a) If n = 360o /   o is odd,

(i) The number of images formed is n, when the object is placed asymmetrically between the mirrors.

(ii) The number of images formed is n-1, when the object is placed symmetrically between the mirrors.

(b) If n = 360o /   o is even, the number of images is always n-1.

Question 2

Two plane mirrors are placed making an angle θ° in between them. For an object placed in between the mirrors, if angle is gradually increased from 0 to 180, how will the number of images change: increase, decrease or remain unchanged?

Answer 2

The number of images formed is given as

So, if q is gradually increased, n decreases.

Question 3

How many images are formed for a point object kept in between two plane mirrors M1 and M2 at right angles to each other? Show them by drawing a ray diagram.

Answer 3

For two mirrors kept perpendicular to each other, three images are formed for an object kept in between them.

m1,m2

Question 4

Two plane mirrors are arranged parallel and facing each other at some separation. How many images are formed for a point object kept in between them? Show the formation of images with the help of a ray diagram

Answer 4

For two mirrors kept parallel to each other, an infinite number of images are formed for an object kept in between them.

Answer 4

Question 5

State two uses of a plane mirror.

Answer 5

Two uses of plane mirror:

  1. In barber’s shop for seeing the hairs at the back of head, two mirrors facing each other are fixed on opposite walls at the front and back of the viewer.
  2. In solar heating devices such as a solar cooker, solar water heater, etc., a plane mirror is used to reflect the incident light rays from sun on the substance to be heated.

MCQ-7(B) Selina Concise 9th physics solution Reflection of Light 

Question 1

Two plane mirrors are placed making an angle 60  in between them. For an object placed in between the mirrors, the number of images formed will be :

(a) 3  (b) 6

(c) 5  (d) infinite.

Answer 1

5

Question 2

In the barber’s shop, two plane mirrors are placed:

(a) Perpendicular to earth other

(b) Parallel to each other

(c) At an angle 60°between them

(d) At angle 45°between them

Answer 2

In a barber’s shop, two plane mirrors are placed parallel to each other.


Num-7(B) Reflection of Light Selina 9th physics solutions

Question 1

State the number of images of an object placed between two mirrors, formed in each case when mirrors are inclined to each other at (a) 90°, and (b) 60°.

Answer 1

(a) Angle between the mirrors,   = 90o

Now, n = 360o /   o = 360o / 90= 4, which is even.

Hence number of images formed will be (n-1); i.e., 4-1 = 3 images

(b) Angle between the mirrors,    = 60o

Now, n = 360o /   o = 360o / 60= 6, which is even.

Hence number of images formed will be (n-1); i.e., 6-1 = 5 images

Question 2

An object is placed (i) asymmetrically (ii) symmetrically, between two plane mirrors inclined at an angle of 50. Find the number of images formed.

Answer 2

Angle between the mirrors,   = 50o

Now, n = 360o /   o = 360o / 50= 7.2     7, which is odd.

(i) When placed asymmetrically, number of images formed will be n, i.e. 7.

(ii) When placed symmetrically, number of images formed will be (n-1); i.e. 7-1 = 6 images


 EXE-7(C) Concise Selina 9th Physics Solutions Reflection of Light

Question 1       

What is a spherical mirror?

Answer 1

A reflecting surface which is a part of a sphere is called a spherical mirror.

Question 2

Name the two kinds of spherical mirrors and distinguish between them.

Answer 2

Two kinds of spherical mirrors are concave and convex.

Distinction between concave and convex mirror: A concave mirror’s bulging surface is silvered and reflection takes place from the hollow surface but a convex mirror’s inner surface is silvered and reflection takes place from the bulging surface.

Question 3

Define the terms pole, principal axis and centre of curvature with reference to a spherical mirror.

Answer 3

Pole: The geometric centre of the spherical surface of mirror is called the pole of mirror.

Principal axis: It is the straight line joining the pole of the mirror to its centre of curvature.

Centre of curvature: The centre of curvature of a mirror is the centre of the sphere of which the mirror is a part.

Question 4

Draw suitable diagrams to illustrate the action of (i) concave mirror and (ii) convex mirror on a beam of light incident parallel to the principal axis.

Answer 4

Answer 4 (a)

Question 5

Name the spherical mirror which (i) diverges (ii) converges the beam of light incident on it. Justify your answer by drawing a ray diagram in each case.

Answer 5

(i) Convex mirror diverges a beam of light falling on it.

curve mirror

Question 6

Define the terms focus and focal length of a concave mirror. Draw diagram to illustrate your answer.

Answer 6

Focus of a concave mirror: The focus of a concave mirror is a point on the principal axis through which the light rays incident parallel to principal axis, pass after reflection from the mirror.

Focal length of a concave mirror: The distance of the focus from the pole of the concave mirror is called its focal length.

concave mirror

Question 7

Explain the meaning of the terms focus and focal length in case of a convex mirror, with the help of suitable ray diagram.

Answer 7

Focus of a convex mirror: The focus of a convex mirror is a point on the principal axis from which, the light rays incident parallel to principal axis, appear to come, after reflection from the mirror.

Focal length of a convex mirror: The distance of the focus from the pole of the convex mirror is called its focal length.

convex mirror

Question 8

State the direction of incident ray which after reflection from a spherical mirror retraces its path. Give a reason to your answer.

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