NCERT Solutions for Class 8 Science Chapter 13 - Light

1. Suppose you are in a dark room. Can you see objects in the room? Can you see objects outside the room? Explain.

Ans: In a dark room, one cannot see things in a room, but things outside the room will be visible. 

The reason for this is that the object is only visible when light from the object reaches the eye. In a dark room, we cannot see objects because the rays of light do not reach our eyes whereas, in a lighted room, the rays of light reflected from the objects reach our eyes making them visible to us.

2. Differentiate between regular and diffused reflection. Does diffused reflection mean the failure of the laws of reflection?

Ans: The difference between regular and diffused reflection is as follows:

Diffused reflection is not due to the failure of the laws of reflection. It is caused by irregularities in the reflecting surface.

3. 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

Ans: A polished surface means the surface is very smooth, thus

regular reflection takes place.

b. Chalk powder

Ans: A diffused reflection takes place on a chalk powder because its surface is uneven.

c. Cardboard surface

Ans: The surface of cardboard that reflects light is not smooth, thus diffused reflection will take place from a cardboard surface.

d. Marble floor with water spread over it

Ans: The water spread over marble makes the surface very

Smooth which makes it act like a plane surface. Hence, regular reflection takes place.

e. Mirror

Ans: The surface of the mirror is very smooth and shiny. Therefore, regular reflection takes place.

f. Piece of paper

Ans: A piece of paper may look smooth, but it has many irregularities on its surface. Thus, diffused reflection takes place.

4. State the laws of reflection.

Ans: Laws of reflection can be stated as follows:

1. The angle of reflection and angle of incidence is always equal to each other.

2. The incident ray, the normal at the point of incidence and the reflected ray all lie in the same plane.

5. 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.

Ans: To perform this experiment take a plane mirror and place it on a plane sheet of paper in a standing position with a block. Then draw an incidence line AB on this paper. Mark the points on the paper by carefully looking at the mirror. The line that goes after it appears on the screen. Draw a perpendicular on the mirror line and then remove the mirror. Join the points to make the reflected ray on the paper. You will observe that incident ray, reflected ray and normal will be in the same plane, i.e. on the sheet of paper. This verifies the law of reflection.

6. 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.

Ans: A person \[1\] m in front of a plane mirror seems to be \[2\] 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 your _________.

Ans: 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.

c. The size of the pupil becomes ________ when you see in dim light.

Ans: The size of the pupil becomes large when you see it in dim light.

d. Night birds have _________ cones than rods in their eyes.

Ans: Night birds have lesser cones than rods in their eyes.

7. The angle of incidence is equal to the angle of reflection.

a. Always

b. Sometimes

c. Under special conditions

d. Never

Ans: (a) Always

Since the first law of reflection states that the angle of incidence and the angle of reflection is always equal to each other.

8. 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.

Ans: (b) Virtual, behind the mirror and of the same size as the object.

The image created by the plane mirror is built behind the mirror. This image cannot be created on screen, so it produces a virtual image of the size that of the object.

9. Describe the construction of a kaleidoscope.

Ans: The Kaleidoscope is made up of three rectangular squares each about \[15\] cm long and \[4\] cm wide which are joined together to build a prism. They are arranged in a circular cardboard tube. Note that the tube is slightly longer than the screen straps. One end of the tube is closed with a cardboard disc with a hole in the middle. To make the disk last longer, a piece of transparent plastic paper is attached to the bottom of the cardboard disk. At the other end, a round plate of the glass plane is fixed touching the mirrors.

10. Draw a labelled sketch of the human eye.

Ans:

11. 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?

Ans: The intensity of the laser light is very high which is harmful to the eye and can cause a permanent defect in the eye. She can lose her eyesight also due to severe damage to the retina. Therefore, it is advisable not to look at a laser beam directly.

12. Explain how you can take care of your eyes.

Ans: To protect our eyes, the following precautions should be taken:

i. Do not read in too little or too much light.

ii. Wash your eyes frequently with cold water.

iii. Do not read by bringing your book too close to your eyes or keeping it too far.

iv. Never rub your eyes.

v. If particles of dust go into our eyes, wash our eyes with clean water. If there is no improvement go to a doctor.

13. What is the angle of incidence of a ray if the reflected ray is at an angle of \[{{90}^{\circ }}\] to the incident ray?

Ans: We know that angle of incidence is equal to the angle of reflection. Therefore, twice of incidence angle is equal to \[{{90}^{\circ }}\].

Thus, Angle of incidence \[i=\dfrac{{{90}^{\circ }}}{2}\] .

\[\Rightarrow i={{45}^{\circ }}\]

14. How many images of a candle will be formed if it is placed between two parallel plane mirrors separated by \[40\] cm?

Ans: Since the mirrors are kept parallel to each other, and Infinite no of images will be formed due to multiple reflections between them.

15. Two mirrors meet at right angles. A ray of light is incident on one at an angle of \[{{30}^{\circ }}\] as shown in Fig. \[16.19\]. Draw the reflected ray from the second mirror.

Ans: From the first law of reflection, The angle of reflection and angle of incidence is always equal to each other.

The diagram of the reflected ray from the second mirror is as follows:

16. 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 \[P,Q,R\]?

Ans:  \[A\] cannot see his image as the length of the mirror is too short on his side. He can see the image of the objects at \[P\] and \[Q\] but cannot see the object at \[R\] as can be inferred from the ray diagram.

17. Solve the below referring to the given diagram.

a. Find out the position of the image of an object situated at \[A\] in the plane mirror.

Ans: The image of \[A\] is formed behind the mirror at the same distance as that of \[A\] from the mirror.

b. Can Paheli at \[B\] see this image?

Ans: Yes, Paheli at \[B\] can see the image.

c. Can Boojho at \[C\] see this image?

Ans: Yes, Boojho at \[C\] can see the image.

d. When Paheli moves from \[B\] to \[C\], where does the image of \[A\] move?

Ans: The image of \[A\] is unaffected by the movement of \[B\] and \[C\]. Therefore, Paheli will be able to see the image of \[A\] while moving from \[B\] to \[C\].

Class 8 Chapter 13 Science Quick Overview Topics Covered

NCERT Chapter 13 Science Class 8 Light- Important Points

• Laws of Reflection: The angle of incidence is equal to the angle of reflection, and the incident ray, reflected ray, and the normal to the surface all lie in the same plane.

• Types of Reflection: Regular reflection (smooth surfaces) and diffuse reflection (rough surfaces).

• Sunlight appears white to the human eye because it combines all visible colours.

• When passed through a prism, sunlight splits into a spectrum of colours, demonstrating that it contains all the visible spectrum colours.

• Dispersion is the process by which white light separates into its component colours.

• Structure of the Human Eye

• Cornea: The eye's transparent, curved front surface that helps to focus incoming light.

• Iris: The coloured part of the eye that controls the size of the pupil and, thus, the amount of light entering the eye.

• Pupil: The black circular opening in the iris regulates the amount of light reaching the retina.

• Lens: A transparent, flexible structure that focuses light onto the retina. It changes shape to adjust the focus (accommodation).

• Retina: The light-sensitive layer at the back of the eye containing photoreceptor cells (rods and cones) that convert light into electrical signals.

• Optic Nerve: Transmits visual information from the retina to the brain.

•  The Braille system is a tactile writing system used by visually impaired people. It enables them to read and write through touch.

Benefits of Vedantu’s Science Chapter 13 Class 8 Question Answer

Referring to NCERT solutions for Class 8 Science Chapter Light offers several benefits:

• NCERT Class 8 Science Chapter Light Question Answer provides clear explanations of concepts covered in the chapter, helping students understand the topic of light thoroughly.

• Light Chapter Of Class 8 PDF Questions And Answers cover important concepts such as the properties of light, reflection, refraction, and the functioning of the human eye.

• Light Chapter Of Class 8 Questions And Answers assists students in completing their last-minute revision efficiently and effectively.

• Class 8 Light Question Answer includes clear diagrams and illustrations, helping students visualise phenomena like the formation of shadows, images by plane mirrors, and the functioning of optical instruments. 

• Class 8 Science Light Solutions includes practice questions and exercises that allow students to test their understanding of the concepts discussed in the chapter.

• By referring to the Light Chapter Of Class 8 Questions And Answers, students can prepare effectively for exams as the solutions cover all the topics and questions likely to be asked in the assessments.

Important Study Materials for Class 8 Chapter 13 Science: Light

Conclusion

Vedantu’s Light Chapter Of Class 8 Questions And Answers is essential for students aiming to understand this topic thoroughly. The solutions focus on key concepts like reflection, refraction, and the properties of light, which are crucial for exams. Students should pay special attention to these areas to grasp the fundamental principles of light. In previous years, around 8 questions from this chapter have appeared in exams, highlighting its importance. Using Vedantu’s solutions, students can clear their doubts, practice effectively, and improve their understanding, ensuring they are well-prepared for their exams.

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Other NCERT Study Resources for Science Class 8

For complete preparation of Science for CBSE Class 8 exams, check out the following links for different study materials available at Vedantu.