Our team of subject expert teachers has prepared and reviewed the NCERT Solutions for Class 8 Science Chapter 16 Light are given here will help you to prepare well and score good numbers in exams.
Light NCERT Solutions for Class 8 Science Chapter 16
Class 8 Science Chapter 16 Light Exercise Questions and Answers
Suppose you are in the darkroom. Can you see objects in the room? Can you see objects outside the room? Explain.
We can see an object from which reflected rays enter our eyes. The light may be emitted by the object or may have been reflected by the object. Thus, we cannot see an object which is placed in a dark room if it does not emit light of its own. Whereas an object outside the dark room can be seen if there is either light outside the dark room or the object emits its own light.
Differentiate between regular and diffused reflection. Does diffused reflection mean the failure of the laws of reflection?
If the reflected rays are parallel to one another, the reflection is called regular reflection. The regular reflection takes place when incident rays fall on the smooth and plane surface like a plane mirror having no defect. When the parallel incident rays fall on a plane mirror having rough or-irregular surfaces, after reflection the rays do not remain parallel. This reflection is called diffused reflection. No, diffused reflection is not the failure of the laws of reflection.
Mention against each of the following whether regular or diffused reflection will take place when a beam of light strikes. Justify your answer in each case.
(a) Polished wooden table.
Regular reflection will take place because the surface is polished.
(b) Chalk powder.
Diffused reflection will take place because it is a rough surface.
(c) Cardboard surface.
Diffused reflection will take place because it is not polished but a rough surface.
(d) Marble floor with water spread over it.
Diffused reflection will take place as marble and water present on the surface of marble together provide an irregular surface to light for reflection.
Regular reflection takes place because a plane mirror is a polished surface.
(f) Piece of paper.
A piece of paper has a rough surface, so diffused reflection will take place.
State the laws of reflection.
There are two laws which govern reflection:
- The incident ray, the normal, and the reflected ray are in. the same plane.
- The angle of reflection is always equal to the angle of incidence.
Describe an activity to show that the incident ray, the reflected ray, and the normal at the point of incidence lie in the same plane.
Materials required: White sheet of stiff paper, a drawing board, drawing pins, a comb, a strip of a plane mirror.
- A white sheet of stiff paper on a drawing board is fixed in such a way that sheet projects a little beyond the edge of the table.
- A comb is taken and all its openings are closed except one in the middle.
- A comb is held perpendicular to the sheet of paper.
- Light is thrown from a torch through the opening of the comb from one side.
- The torch and the comb are so adjusted that a ray of light along the paper on the other side of the comb is visible.
- A strip of plane mirror is placed in the path of the light ray.
- After striking the mirror, the incident ray is reflected, and the reflected ray is seen on the paper.
- The projected portion of the .sheet is cut in the middle. It was made sure that the reflected ray extends to the projected portion of the paper.
- The part of the projected portion on which the reflected ray fell was bent,
- Try to see the reflected ray was made.
- The paper was brought to its original position and again a ray was made to see the reflected ray again.
Observations: When the whole sheet of paper was spread on the table, it represented one plane. The incident ray, the reflected ray, and the normal at the point of incidence were seen on it. But when the sheet was bent, i.e., a plane different from the plane, in which the incident ray and the normal ray, was created. In this case, we were not able to see the reflected ray [See Fig. 16.4 (a) and (b) on Page 201, NCERT],
This activity shows that the incident ray, the normal at the point of incidence, and the reflected ray all lie in the same plane.
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 your right hand in front of a plane mirror it will be seen in the mirror that your right ear is touched with
Left Left hand
(c) The size of the pupil becomes ______ when you see it in dim light.
(d) Night birds have ______ cones than rods in their eyes.
The angle of incidence is equal to the angle of reflection.
(c) Under special conditions
The 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.
(b) virtual, behind the mirror and of the same size as the object.
Describe the construction of a kaleidoscope.
Kaleidoscope is a scientific toy which contains three rectangular mirrors fixed length-wise at an angle of 60° to each other. This arrangement of the mirror is placed in a cylindrical cardboard box with small coloured objects at one end. When Kaleidoscope placed towards light and the tube is rotated, the tumbling of the coloured objects presents varying patterns to the observer. Designers and artists use Kaleidoscope to get ideas for new patterns to design wallpapers, jewellery, and fabrics.
Draw a labeled sketch of the human eye.
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?
Laser torch can harm or even damage the eye. So, her teacher advised her not to do so.
Explain how you can take care of your eyes?
It is necessary that we take proper care of our eyes. If there is any problem we should go to an eye specialist for a regular checkup. We must:
- If advised, use suitable spectacles.
- Too little or too much light is bad for the eyes. Insufficient light causes eyestrain and headaches.
- Too much light, like that of the sun, or powerful lamps, can injure the retina, which is very delicate.
- Do not look at the sun or a powerful light directly.
- Never rub your eyes if any small particle of dust goes into them. Wash your eyes with clean water. If the condition does not improve, then contact a doctor.
- Wash your eyes frequently with clean water.
- Always read at the normal distance for vision.
What is the angle of incidence of a ray if the reflected ray is at an angle of 90° to the incident ray?
The angle of incidence is 90°.
(As the angle of incidence = Angle of reflection)
How many images of a candle will be formed if it is placed between two parallel plane mirrors separated by 40 cm?
An infinite number of images will be formed.
Two mirrors meet at right angles. A ray of light is incident on one at an angle of 30° as shown in the figure. Draw the reflected ray from the second mirror.
Boojho stands at A just on the side of a plane mirror as shown in the figure. Can he see himself in the mirror? Also, can he see the image of objects situated at P and Q, and R?
Boojho will not be able to see himself in the mirror. But he can see images of objects situated at ‘P and Q and R.
(a) Find out the position of the image of an object situated at A in the plane mirror.
(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?
(a) The image will be formed at the same distance behind the mirror.
(d) The image remains at the same place. The image moves only if the object or the mirror is moved.
Class 8 Science Chapter 16 Light InText Questions and Answers
How is seeing made possible?
When light from an object enters our eyes, we see the object.
16.1 What makes Things Visible
Can you see an object in the dark?
No, for seeing an object light is also required.
Can you tell in which direction the light falling on a surface will be reflected?
The light ray, which strikes any surface, reflects in another direction.
16.2 Laws of Reflection Activity 16.1
What do you observe?
After striking the mirror, the ray of light is reflected in another direction.
Enter the data in Table 16.1 (Textbook page 200):
|S.NO.||The angle of incidence (<i)||The angle of reflection (<r)|
Do you see any relation between the angle of incidence and the angle of reflection? Are they approximately equal?
Yes, we can see a relation between the angle of incidence and the angle of reflection. They are approximately equal.
What would happen if I threw the light on the mirror along the normal?
The light will reflect along the normal only.
What do you infer?
The incident ray, the normal at the point of incidence, and the reflected ray all lie in the same plane.
Paheli asked him to recall those features:
(1) Was the image erector upside down?
It was erect.
(2) Was it of the same size as the object?
(3) Did the image appear at the same? the distance behind the mirror as the object was in front of it?
Yes, the image formed was at the same distance behind the mirror as the object was in front of it.
(4) Could it be obtained on a screen?
No, it could not be. obtained on a screen, because it was a virtual image.
Extend them further. Do they meet? Extend them backward. Do they meet now?
No, the reflected rays do not meet on the further extension. On extending backward, the reflected rays meet at a point.
16.3 Regular and Diffused Reflection Activity 16.4
Are they parallel to one another?
No, the reflected rays are not parallel to one another.
I have a question. Can the reflected rays be further reflected in the incident on another mirror?
“Yes, reflected rays can be further reflected in the incident on another mirror.
16.4 Reflected Light can be Reflected Again
Do you know how you could see the hair at the back of your head?
The hack of the head can be seen due to the reflection of light from the mirror placed at the back of the head.
Can you explain how reflection from the two mirrors enables you to see objects which are not visible directly?
Yes, it is because reflected rays from one mirror are reflected again by another mirror. This phenomenon is also performed in a periscope.
16.5 Multiple Images
What happens if two plane mirrors are used in combination?
A number of images are formed if we place .two mirrors at an angle to one another.
How many images of the coin do you see (Fig. 16.10, Textbook page 204)?
Can you now explain how you can see the back of your head at the hairdresser’s shop?
Yes. The back of the head can be seen due to the reflection of light from the mirror placed at the back of the head.
How can you explain this?
As the mirror and water together form a prism, it breaks up the light into its constituent seven colors on the paper.
Do you notice any change in the size of the pupil? In which case was the pupil larger? Why do you think it was so?
When the light from the torch falls on the pupil, its size becomes smaller to allow less amount of light to enter into the eye. When the light was not falling on the pupil, its size was bigger, to allow more light to enter into the eye for distinct vision. It happened so to control the amount of light entering into the eye.
In which case do you need to allow more light in the eye, when the light is dim or bright?
When the light is dim, we need to allow more light in the eye.
What kind of lens is thicker at the center?
Do you see the bird in the cage?
Yes, I can see.