Selina Textbook Solutions: Reflection of Light | Physics Class 9 ICSE PDF Download

 Page 1


Chapter 7. Reflection of Light
Exercise 7(A)
Solution 1S.
The return of light into the same medium after striking a surface is called reflection.
Solution 2S.
Black silvered surface reflects most of the light incident on it.
Solution 3S.
(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. 
 
(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. 
Page 2


Chapter 7. Reflection of Light
Exercise 7(A)
Solution 1S.
The return of light into the same medium after striking a surface is called reflection.
Solution 2S.
Black silvered surface reflects most of the light incident on it.
Solution 3S.
(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. 
 
(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. 
Solution 4S.
 
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.
Solution 5S.
Page 3


Chapter 7. Reflection of Light
Exercise 7(A)
Solution 1S.
The return of light into the same medium after striking a surface is called reflection.
Solution 2S.
Black silvered surface reflects most of the light incident on it.
Solution 3S.
(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. 
 
(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. 
Solution 4S.
 
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.
Solution 5S.
Reflection of light from a plane mirror is regular reflection and reflection of light from 
plane sheet of paper is irregular reflection of light.
Solution 6S.
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.
Solution 7S.
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.
Experiment to verify the laws of reflection:
Fix a white sheet of paper on a drawing board and draw a line MM
1 
as shown in figure. 
On this line, take a point O nearly at the middle of it and draw a line OA such that ?MOA 
is less than 90
o
. Then draw a normal ON on line MM
1
 at the point O, and place a small 
plane mirror vertical by means of a stand with its silvered surface along MM
1
.
Next fix two pins P and Q at some distance (˜5 cm) apart vertically on line OA, on the 
board. Keeping eye on the other side of normal (but on the same side of mirror), see 
clearly images P’ and Q’ of the pins P and Q. Next fix a pin R such that it is in line with 
the images of pins P and Q as observed in the mirror. Next, fix one more pin S such that 
the pin S is in line with the pin R as well as images P’ and Q’ of pins P and Q.
Draw small circles on paper around the positions of pins as shown in figure. Remove the 
pins and draw a line OB joining the pin points S and R, which meets the surface of mirror 
at O. The angles AON and BON are measured and recorded.
Page 4


Chapter 7. Reflection of Light
Exercise 7(A)
Solution 1S.
The return of light into the same medium after striking a surface is called reflection.
Solution 2S.
Black silvered surface reflects most of the light incident on it.
Solution 3S.
(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. 
 
(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. 
Solution 4S.
 
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.
Solution 5S.
Reflection of light from a plane mirror is regular reflection and reflection of light from 
plane sheet of paper is irregular reflection of light.
Solution 6S.
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.
Solution 7S.
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.
Experiment to verify the laws of reflection:
Fix a white sheet of paper on a drawing board and draw a line MM
1 
as shown in figure. 
On this line, take a point O nearly at the middle of it and draw a line OA such that ?MOA 
is less than 90
o
. Then draw a normal ON on line MM
1
 at the point O, and place a small 
plane mirror vertical by means of a stand with its silvered surface along MM
1
.
Next fix two pins P and Q at some distance (˜5 cm) apart vertically on line OA, on the 
board. Keeping eye on the other side of normal (but on the same side of mirror), see 
clearly images P’ and Q’ of the pins P and Q. Next fix a pin R such that it is in line with 
the images of pins P and Q as observed in the mirror. Next, fix one more pin S such that 
the pin S is in line with the pin R as well as images P’ and Q’ of pins P and Q.
Draw small circles on paper around the positions of pins as shown in figure. Remove the 
pins and draw a line OB joining the pin points S and R, which meets the surface of mirror 
at O. The angles AON and BON are measured and recorded.
The experiment is then repeated for the angle of incidence ?AON equal to 40
o
, 50
o
, 60
o
. 
From results, it is observed that angle of incidence is equal to the angle of reflection. This 
verifies the first law of reflection.
The experiment has been performed on a flat drawing board, with mirror normal to the 
plane of board on which white sheet of paper is being fixed. Since the lower tips of all the 
pins also lie on the same plane (i.e., the plane of paper), it proves the second law of 
reflection.
Solution 8S.
Solution 9S.
Solution 10S.
(a) Angle of incidence = 90
o 
– 30
o
 = 60
o 
(b) Angle between the incident ray and reflected ray = Angle of incidence + Angle of 
reflection 
Page 5


Chapter 7. Reflection of Light
Exercise 7(A)
Solution 1S.
The return of light into the same medium after striking a surface is called reflection.
Solution 2S.
Black silvered surface reflects most of the light incident on it.
Solution 3S.
(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. 
 
(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. 
Solution 4S.
 
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.
Solution 5S.
Reflection of light from a plane mirror is regular reflection and reflection of light from 
plane sheet of paper is irregular reflection of light.
Solution 6S.
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.
Solution 7S.
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.
Experiment to verify the laws of reflection:
Fix a white sheet of paper on a drawing board and draw a line MM
1 
as shown in figure. 
On this line, take a point O nearly at the middle of it and draw a line OA such that ?MOA 
is less than 90
o
. Then draw a normal ON on line MM
1
 at the point O, and place a small 
plane mirror vertical by means of a stand with its silvered surface along MM
1
.
Next fix two pins P and Q at some distance (˜5 cm) apart vertically on line OA, on the 
board. Keeping eye on the other side of normal (but on the same side of mirror), see 
clearly images P’ and Q’ of the pins P and Q. Next fix a pin R such that it is in line with 
the images of pins P and Q as observed in the mirror. Next, fix one more pin S such that 
the pin S is in line with the pin R as well as images P’ and Q’ of pins P and Q.
Draw small circles on paper around the positions of pins as shown in figure. Remove the 
pins and draw a line OB joining the pin points S and R, which meets the surface of mirror 
at O. The angles AON and BON are measured and recorded.
The experiment is then repeated for the angle of incidence ?AON equal to 40
o
, 50
o
, 60
o
. 
From results, it is observed that angle of incidence is equal to the angle of reflection. This 
verifies the first law of reflection.
The experiment has been performed on a flat drawing board, with mirror normal to the 
plane of board on which white sheet of paper is being fixed. Since the lower tips of all the 
pins also lie on the same plane (i.e., the plane of paper), it proves the second law of 
reflection.
Solution 8S.
Solution 9S.
Solution 10S.
(a) Angle of incidence = 90
o 
– 30
o
 = 60
o 
(b) Angle between the incident ray and reflected ray = Angle of incidence + Angle of 
reflection 
Angle of reflection = Angle of incidence = 60
o 
Therefore, Angle between the incident ray and reflected ray = 60
o
 + 60
o
 = 120
o
Solution 11S.
Solution 12S.