NCERT Solutions for Class 8 Science Chapter 13 Light
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Page 1
NCERT
SOLUTIONS
CLASS - 8TH
aglase .co
SOLUTIONS
CLASS - 8TH
aglase .co
Page 2
Class : 8th
Subject : Science
Chapter : 16
Chapter Name : LIGHT
Q1 Suppose you are in a dark room. Can you see objects in the room? Can you see objects
outside the room. Explain.
Answer. If we are in a dark room, then it is not possible for us to see objects in the room.
However, objects outside the room are visible to us. An object becomes visible when light
reaches our eye after being re�ected from the object. If there is no light in the room,
then the objects inside the room cannot re�ect any light. Hence, we cannot see in a dark
room. If there is light present outside the room, then we can see the objects outside the
room.
Q2 Differentiate between regular and diffused re�ection. Does diffused re�ection mean
the failure of the laws of re�ection?
Answer. Regular re�ection takes place from a smooth or a regular surface. In regular
re�ection, all re�ected rays are parallel to each other for parallel incident rays.
Irregular or diffused re�ection takes place from an irregular surface. In diffused
re�ection, the re�ected rays are not parallel to each other for parallel incident rays.
This happens because of the presence of irregular microscopic surfaces. Hence, parallel
incident rays re�ect in different directions. However, each ray obeys the laws of
re�ection. Therefore, laws of re�ections are not violated in diffused or irregular
re�ections.
Q3 Mention against each of the following whether regular or diffused re�ection will take
place when a beam of light strikes. Justify your answer in each case.
(a) Polished wooden table
(b) Chalk powder
(c) Cardboard surface
(d) Marble �oor with water spread over it
(e) Mirror
(f) Piece of paper
Page 1 of 8 Aglasem Schools
Subject : Science
Chapter : 16
Chapter Name : LIGHT
Q1 Suppose you are in a dark room. Can you see objects in the room? Can you see objects
outside the room. Explain.
Answer. If we are in a dark room, then it is not possible for us to see objects in the room.
However, objects outside the room are visible to us. An object becomes visible when light
reaches our eye after being re�ected from the object. If there is no light in the room,
then the objects inside the room cannot re�ect any light. Hence, we cannot see in a dark
room. If there is light present outside the room, then we can see the objects outside the
room.
Q2 Differentiate between regular and diffused re�ection. Does diffused re�ection mean
the failure of the laws of re�ection?
Answer. Regular re�ection takes place from a smooth or a regular surface. In regular
re�ection, all re�ected rays are parallel to each other for parallel incident rays.
Irregular or diffused re�ection takes place from an irregular surface. In diffused
re�ection, the re�ected rays are not parallel to each other for parallel incident rays.
This happens because of the presence of irregular microscopic surfaces. Hence, parallel
incident rays re�ect in different directions. However, each ray obeys the laws of
re�ection. Therefore, laws of re�ections are not violated in diffused or irregular
re�ections.
Q3 Mention against each of the following whether regular or diffused re�ection will take
place when a beam of light strikes. Justify your answer in each case.
(a) Polished wooden table
(b) Chalk powder
(c) Cardboard surface
(d) Marble �oor with water spread over it
(e) Mirror
(f) Piece of paper
Page 1 of 8 Aglasem Schools
Page 3
Answer. (a) Polished wooden table → Regular re�ection
A polished surface is an example of a smooth surface. A polished wooden table has a
smooth surface. Hence, re�ections from the polished table will be regular.
(b) Chalk powder → Diffused re�ection
Chalk power spread on a surface is an example of an irregular surface. It is not smooth.
Therefore, diffused re�ection will take place from chalk powder.
(c) Cardboard surface → Diffused re�ection
Cardboard surface is also an example of an irregular surface. Hence, diffused re�ection
will take place from a cardboard surface.
(d) Marble �oor with water spread over it → Regular re�ection
Marble �oor with water spread over it is an example of a regular surface. This is because
water makes the marble surface smooth. Hence, regular re�ection will take place from
this surface.
(e) Mirror → Regular re�ection
Mirror has a smooth surface. Therefore, it will give a regular re�ection.
(f) Piece of paper → Diffused re�ection
Although a piece of paper may look smooth, but it has many irregularities on its surface.
Due to this reason, it will give a diffused re�ection.
Q4 State the laws of re�ection.
Answer. Laws of re�ection:
(i) The angle of re�ection is always equal to the angle of incidence.
(ii) The incident ray, the re�ected ray and the normal to the re�ective surface
at the point of incidence all lie in the same plane.
Q5 Describe an activity to show that the incident ray, the re�ected ray and the normal at
the point of incidence lie in the same plane.
Answer. Place a plane mirror on the table. Take a paper sheet and make a small hole in
its centre. Make sure that the light in the room is not bright. Hold the sheet normal to
the table. Take another sheet and place it on the table in contact with the vertical mirror.
Draw a normal line on the second sheet from the mirror. Now, light a torch on the mirror
through the small hole such that the ray of light falls on the normal at the bottom of the
mirror. When the ray from this hole is incident on the mirror, it gets re�ected in a certain
direction. You can easily observe the incident ray, re�ected ray and the normal to the
Page 2 of 8 Aglasem Schools
A polished surface is an example of a smooth surface. A polished wooden table has a
smooth surface. Hence, re�ections from the polished table will be regular.
(b) Chalk powder → Diffused re�ection
Chalk power spread on a surface is an example of an irregular surface. It is not smooth.
Therefore, diffused re�ection will take place from chalk powder.
(c) Cardboard surface → Diffused re�ection
Cardboard surface is also an example of an irregular surface. Hence, diffused re�ection
will take place from a cardboard surface.
(d) Marble �oor with water spread over it → Regular re�ection
Marble �oor with water spread over it is an example of a regular surface. This is because
water makes the marble surface smooth. Hence, regular re�ection will take place from
this surface.
(e) Mirror → Regular re�ection
Mirror has a smooth surface. Therefore, it will give a regular re�ection.
(f) Piece of paper → Diffused re�ection
Although a piece of paper may look smooth, but it has many irregularities on its surface.
Due to this reason, it will give a diffused re�ection.
Q4 State the laws of re�ection.
Answer. Laws of re�ection:
(i) The angle of re�ection is always equal to the angle of incidence.
(ii) The incident ray, the re�ected ray and the normal to the re�ective surface
at the point of incidence all lie in the same plane.
Q5 Describe an activity to show that the incident ray, the re�ected ray and the normal at
the point of incidence lie in the same plane.
Answer. Place a plane mirror on the table. Take a paper sheet and make a small hole in
its centre. Make sure that the light in the room is not bright. Hold the sheet normal to
the table. Take another sheet and place it on the table in contact with the vertical mirror.
Draw a normal line on the second sheet from the mirror. Now, light a torch on the mirror
through the small hole such that the ray of light falls on the normal at the bottom of the
mirror. When the ray from this hole is incident on the mirror, it gets re�ected in a certain
direction. You can easily observe the incident ray, re�ected ray and the normal to the
Page 2 of 8 Aglasem Schools
Page 4
Book : Science Ncert Solutions | Chapter-16 Science
mirror at the point of incidence on the sheet placed on the table. This shows that the
incident ray, the re�ected ray, and the normal to the surface at the point of incidence all
lie in the same plane.
Q6 Fill in the blanks in the following.
(a) A person 1 m in front of a plane mirror seems to be _______________ m away from his
image.
(b) If you touch your ____________ ear with right hand in front of a plane mirror it will be
seen in the mirror that your right ear is touched with ____________.
(c) The size of the pupil becomes ____________ when you see in dim light.
(d) Night birds have ____________ cones than rods in their eyes.
Answer. (a) A person 1 m in front of a plane mirror seems to be __2 __ m away from his
image.
(Object distance and image distance are the same from a plane mirror. The image of a
person 1 m in front of a mirror is 1 m back to the mirror. Hence, the image is 1 + 1 = 2 m
away from the person.)
(b) If you touch your __left__ ear with your right hand in front of a plane mirror, it will be
seen in the mirror that your right ear is touched with your _left hand_.
(This is because of lateral inversion of images formed in a plane mirror.)
(c) The size of the pupil becomes __large__ when you see in dim light.
(In dim light, the amount of light entering the eye is very little. To increase the amount
of light, the pupil expands. )
(d) Night birds have __less__ cones than rods in their eyes.
(Night birds can see in the night, but not in the day. They have on their retina a large
number of rod cells and only a few cones.)
Page 3 of 8 Aglasem Schools
mirror at the point of incidence on the sheet placed on the table. This shows that the
incident ray, the re�ected ray, and the normal to the surface at the point of incidence all
lie in the same plane.
Q6 Fill in the blanks in the following.
(a) A person 1 m in front of a plane mirror seems to be _______________ m away from his
image.
(b) If you touch your ____________ ear with right hand in front of a plane mirror it will be
seen in the mirror that your right ear is touched with ____________.
(c) The size of the pupil becomes ____________ when you see in dim light.
(d) Night birds have ____________ cones than rods in their eyes.
Answer. (a) A person 1 m in front of a plane mirror seems to be __2 __ m away from his
image.
(Object distance and image distance are the same from a plane mirror. The image of a
person 1 m in front of a mirror is 1 m back to the mirror. Hence, the image is 1 + 1 = 2 m
away from the person.)
(b) If you touch your __left__ ear with your right hand in front of a plane mirror, it will be
seen in the mirror that your right ear is touched with your _left hand_.
(This is because of lateral inversion of images formed in a plane mirror.)
(c) The size of the pupil becomes __large__ when you see in dim light.
(In dim light, the amount of light entering the eye is very little. To increase the amount
of light, the pupil expands. )
(d) Night birds have __less__ cones than rods in their eyes.
(Night birds can see in the night, but not in the day. They have on their retina a large
number of rod cells and only a few cones.)
Page 3 of 8 Aglasem Schools
Page 5
Book : Science Ncert Solutions | Chapter-16 Science
Q7 Angle of incidence is equal to the angle of re�ection.
(a) Always
(b) Sometimes
(c) Under special conditions
(d) Never
Answer. (a) The angle of incidence is always equal to the angle of re�ection. This is the
�rst law of re�ection.
Q8 Image formed by a plane mirror is
(a) virtual, behind the mirror and enlarged.
(b) virtual, behind the mirror and of the same size as the object.
(c) real at the surface of the mirror and enlarged.
(d) real, behind the mirror and of the same size as the object.
Answer. (b) Image formed by a plane mirror is virtual, behind the mirror and of the same
size as the object.
The image formed by a plane mirror is of the same size as the object. The image is
formed behind the mirror. The image cannot be obtained on a screen. Hence, it is a
virtual image.
Q9 Describe the construction of a kaleidoscope.
Answer. Construction of a kaleidoscope:
Three rectangular mirror strips of dimensions 15 cm × 4cm (l × b) are joined together to
form a prism (�g a). This prism is �xed into a circular cardboard tube.
The circular cardboard tube should be slightly longer that the prism (�g b). This circular
tube is now closed at one end with a cardboard disc. This disc has a hole in it through
which we can see (�g c) .At the other end of the circular tube, a plane glass plate is �xed.
It is important that this glass plate touches the prism mirrors. On this glass plate, several
small and broken pieces of coloured glass are placed. This end is now closed by a round
glass plate allowing enough space for the coloured glass pieces to move (�g d).
Page 4 of 8 Aglasem Schools
Q7 Angle of incidence is equal to the angle of re�ection.
(a) Always
(b) Sometimes
(c) Under special conditions
(d) Never
Answer. (a) The angle of incidence is always equal to the angle of re�ection. This is the
�rst law of re�ection.
Q8 Image formed by a plane mirror is
(a) virtual, behind the mirror and enlarged.
(b) virtual, behind the mirror and of the same size as the object.
(c) real at the surface of the mirror and enlarged.
(d) real, behind the mirror and of the same size as the object.
Answer. (b) Image formed by a plane mirror is virtual, behind the mirror and of the same
size as the object.
The image formed by a plane mirror is of the same size as the object. The image is
formed behind the mirror. The image cannot be obtained on a screen. Hence, it is a
virtual image.
Q9 Describe the construction of a kaleidoscope.
Answer. Construction of a kaleidoscope:
Three rectangular mirror strips of dimensions 15 cm × 4cm (l × b) are joined together to
form a prism (�g a). This prism is �xed into a circular cardboard tube.
The circular cardboard tube should be slightly longer that the prism (�g b). This circular
tube is now closed at one end with a cardboard disc. This disc has a hole in it through
which we can see (�g c) .At the other end of the circular tube, a plane glass plate is �xed.
It is important that this glass plate touches the prism mirrors. On this glass plate, several
small and broken pieces of coloured glass are placed. This end is now closed by a round
glass plate allowing enough space for the coloured glass pieces to move (�g d).
Page 4 of 8 Aglasem Schools
Page 6
Q10 Draw a labelled sketch of the human eye.
Answer.
Q11 Gurmit wanted to perform Activity 16.8 using a laser torch. Her teacher advised her
not to do so. Can you explain the basis of the teacher’s advice?
Answer. Laser light is harmful for the human eyes, because its intensity is very high. It
can cause damage to the retina and lead to blindness. Hence, it is advisable not to look at
a laser beam directly.
Page : 213 , Block name : Exercise
Page 5 of 8 Aglasem Schools
Answer.
Q11 Gurmit wanted to perform Activity 16.8 using a laser torch. Her teacher advised her
not to do so. Can you explain the basis of the teacher’s advice?
Answer. Laser light is harmful for the human eyes, because its intensity is very high. It
can cause damage to the retina and lead to blindness. Hence, it is advisable not to look at
a laser beam directly.
Page : 213 , Block name : Exercise
Page 5 of 8 Aglasem Schools
Page 7
Book : Science Ncert Solutions | Chapter-16 Science
Q12 Explain how you can take care of your eyes.
Answer. To protect our eyes, the given points should be taken into account:
(i) Visit an eye specialist regularly.
(ii) Avoid reading in dim light and very bright light.
(iii) Avoid direct exposure of sunlight to the eye.
(iv) Clean your eyes with cold water quickly if dust particles or small insects enter your
eye. Do not rub your eyes.
(v) Maintain a distance of at least 25 cm between the book and your eyes while reading.
Page : 213 , Block name : Exercise
Q13 What is the angle of incidence of a ray if the re�ected ray is at an angle of 90° to the
incident ray?
Answer. If the re�ected ray is at an angle of 90° to the incident ray, then the angle of
incidence is 45 °. According to the law of re�ection, the angle of incidence is equal to the
angle of re�ection. Therefore, the angle of incidence and the angle of re�ection both are
= (90/2) = 45°.
Page : 213 , Block name : Exercise
Q14 How many images of a candle will be formed if it is placed between two parallel
plane mirrors separated by 40 cm?
Answer. In�nite or multiple images of the candle will be formed because of multiple
re�ections between the mirrors. When two mirrors are placed parallel to each other, then
in�nite numbers of images are formed.
Page : 213 , Block name : Exercise
Q15 Two mirrors meet at right angles. A ray of light is incident on one at an angle of 30°
as shown in Fig. 16.19. Draw the re�ected ray from the second mirror.
Page 6 of 8 Aglasem Schools
Q12 Explain how you can take care of your eyes.
Answer. To protect our eyes, the given points should be taken into account:
(i) Visit an eye specialist regularly.
(ii) Avoid reading in dim light and very bright light.
(iii) Avoid direct exposure of sunlight to the eye.
(iv) Clean your eyes with cold water quickly if dust particles or small insects enter your
eye. Do not rub your eyes.
(v) Maintain a distance of at least 25 cm between the book and your eyes while reading.
Page : 213 , Block name : Exercise
Q13 What is the angle of incidence of a ray if the re�ected ray is at an angle of 90° to the
incident ray?
Answer. If the re�ected ray is at an angle of 90° to the incident ray, then the angle of
incidence is 45 °. According to the law of re�ection, the angle of incidence is equal to the
angle of re�ection. Therefore, the angle of incidence and the angle of re�ection both are
= (90/2) = 45°.
Page : 213 , Block name : Exercise
Q14 How many images of a candle will be formed if it is placed between two parallel
plane mirrors separated by 40 cm?
Answer. In�nite or multiple images of the candle will be formed because of multiple
re�ections between the mirrors. When two mirrors are placed parallel to each other, then
in�nite numbers of images are formed.
Page : 213 , Block name : Exercise
Q15 Two mirrors meet at right angles. A ray of light is incident on one at an angle of 30°
as shown in Fig. 16.19. Draw the re�ected ray from the second mirror.
Page 6 of 8 Aglasem Schools
Page 8
Answer. The �rst law of re�ection is used to obtain the path of re�ected light.
It can be observed that the given ray of light will re�ect from the second mirror at an
angle 60°.
Page : 213 , Block name : Exercise
Q16 Boojho stands at A just on the side of a plane mirror as shown in Fig. 16.20. Can he
see himself in the mirror? Also can he see the image of objects situated at P, Q and R?
Answer. A plane mirror forms a virtual image behind the mirror. The image is as far
behind the mirror as the object is in front of it. A cannot see his image because the
length of the mirror is too short on his side. However, he can see the objects placed at
points P and Q, but cannot see the object placed at point R (as shown in the given �gure).
Page 7 of 8 Aglasem Schools
It can be observed that the given ray of light will re�ect from the second mirror at an
angle 60°.
Page : 213 , Block name : Exercise
Q16 Boojho stands at A just on the side of a plane mirror as shown in Fig. 16.20. Can he
see himself in the mirror? Also can he see the image of objects situated at P, Q and R?
Answer. A plane mirror forms a virtual image behind the mirror. The image is as far
behind the mirror as the object is in front of it. A cannot see his image because the
length of the mirror is too short on his side. However, he can see the objects placed at
points P and Q, but cannot see the object placed at point R (as shown in the given �gure).
Page 7 of 8 Aglasem Schools
Page 9
Page : 213 , Block name : Exercise
Q17 (a) Find out the position of the image of an object situated at A in the plane mirror
(Fig. 16.21).
(b) Can Paheli at B see this image?
(c) Can Boojho at C see this image?
(d) When Paheli moves from B to C, where does the image of A move?
Answer. (a) Image of the object placed at A is formed behind the mirror. The distance of
the image from the mirror is equal to the distance of A from the mirror. Image of A is
shown in the given �gure.
(b) Yes. Paheli at B can see this image.
(c) Yes. Boojho at C can see this image.
(d) Image of the object at A will not move. It will remain at the same position when
Paheli moves from B to C.
Page : 213 , Block name : Exercise
Page 8 of 8 Aglasem Schools
Q17 (a) Find out the position of the image of an object situated at A in the plane mirror
(Fig. 16.21).
(b) Can Paheli at B see this image?
(c) Can Boojho at C see this image?
(d) When Paheli moves from B to C, where does the image of A move?
Answer. (a) Image of the object placed at A is formed behind the mirror. The distance of
the image from the mirror is equal to the distance of A from the mirror. Image of A is
shown in the given �gure.
(b) Yes. Paheli at B can see this image.
(c) Yes. Boojho at C can see this image.
(d) Image of the object at A will not move. It will remain at the same position when
Paheli moves from B to C.
Page : 213 , Block name : Exercise
Page 8 of 8 Aglasem Schools
Document Details
| Board / Org | NCERT |
| Exam | Class 8 |
| Type | Solution |
| Pages | 9 |
| Language | english |
| Updated | 22 Jul 2026 |