Important Questions Class 8 Science Chapter 16

Important Questions Class 8 Science Chapter 16 – Light

Chapter 16 of Class 8 Science is about Light. The chapter Light starts with the concepts and meaning of light and the laws of reflection. Students might have already heard the word reflection in the previous chapter. In this unit, students learn what reflection is and what laws are associated with it.  This chapter will answer the most common questions in students’ minds, like how can a visually impaired person read. How can an owl see only at night but not during daylight? What is the braille system? And other such questions. In this chapter, you will also study the human eye and the construction of the human eye. Students will also learn fun experiments for explaining reflections, such as how to build a kaleidoscope. By completing this chapter, students will be capable of understanding many interesting concepts

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Important Questions Class 8 Science Chapter 16 – With Solutions

Considering that our team has collated questions from different sources in one place, our question bank of Class 8 Science Chapter 16 Important Questions has proven helpful for a lot of students. Our Science expert faculty members have prepared detailed and step-by-step instruction-based answers for each of the questions covered in our question bank. Students will be able to fully revise the chapter while they are solving questions.

Below are a few questions and their solutions from our question bank of Important Questions Class 8 Science Chapter 16.

Question 1. Image formed in a plane mirror undergoes _______________. 

Answer 1. lateral inversion.

The reversal of a mirror image, where the object’s right side appears on the left side behind the mirror, is known as lateral inversion.

Question 2. Name the part of the eye that gives a distinctive colour. 

Answer 2. Iris is the part of our eye that gives us distinctive colour. The iris is a coloured ring that surrounds our pupils and gives our eyes their distinct colour.

Question 3. The lens that focuses light on the back of the eye, on a layer called___________. 

Answer 3. Retina.

Several thousand light-sensitive cells (rods and cones) and some other nerve cells make up the retina, which receives and organises visual data. Through our optic nerve, retina sends this information to  brain, allowing us to see.

Question 4. What is a blind spot?

Answer 4. There are no sensory cells at the optic nerve and the retina intersection. Hence, vision is not possible there. This is known as the blind spot.

Question 5. ____________ are sensitive to bright light in eye.

Answer 5. Cones.

In the retina, cones are a kind of photoreceptor cell. They are responsible for our colour perception. Cones are concentrated in the macula, located in the centre of our retina and help us see small details.

Question 6. Lack of which nutrient element is responsible for eye troubles?

Answer 6. The deficiency of Vitamin A causes eye troubles. Xerophthalmia is a progressive eye problem caused by a lack of vitamin A. Xerophthalmia can progress to night blindness or more serious damage to the cornea, the outer layer of the eye.

Question 7. Some persons may lose their vision because of a _________ or an __________. 

Answer 7. Disease, injury.

Question 8. Who developed a system for visually impaired people and published it in 1821? 

Answer 8. The Braille system was developed in the 1820s by Louis Braille and is the most commonly used resource for visually challenged people. Blind individuals read and write using the Braille system. A set of raised bumps or dots can be sensed with the help of a finger in the Braille system.

Question 9. Do you think a light ray is an idealisation? Why? 

Answer 9. Yes, a ray of light is an idealisation. A narrow beam of light is made up of several rays. For simplicity, the word ray is used for a little light beam.

Question 10. Give any two uses of the periscope. 

Answer 10. Tanks, submarines, and soldiers in bunkers use periscopes to see things outside.

Question 11. List the food items that contain vitamin A.

Answer 11. Vitamin A is abundant in raw carrots, broccoli, green vegetables (such as spinach), and cod liver oil. Vitamin A is found in eggs, milk, curd, cheese, butter, and fruits like papaya and mango.

Question 12. State laws of reflection.

Answer 12. ‘The incidence angle is equal to the reflection angle,’ says the first law of reflection.

The incident reflected, and normal rays drawn at the point of incidence to the reflecting surface lie in the same plane, per the second law of reflection.

Question 13. Give any four examples of luminous objects.

 Answer 13. The sun, fire, candle flame, and an electric lamp are luminous objects.

Question 14. Explain regular reflection with the help of a diagram. 

Answer 14. A regular reflection is a reflection made from a smooth surface like a mirror. Regular reflection creates images.

Question 15. What is the function of the retina? 

Answer 15. The lens directs incident light to the retina, which includes several nerve cells. The nerve cells’ sensations are then transferred to the brain through the optic nerve.

Question 16. Give an example to show that reflected light can be reflected again. 

Answer 16.  Stand in front of a mirror and ask a friend to hold a mirror behind you so you can see your haircut; your hair image will appear in the mirror in front of you; this is the best example of reflected light returning to the source.

Question 17. Can we see objects in the dark? Why? 

Answer 17. When the incident light is reflected by the object and reaches our eyes, we can see it. However, when the object reflects no light, we cannot see it.

Question 18. How do you make a kaleidoscope?

Answer 18. Make three small rectangular mirror strips, each about 15 cm long and 4 cm wide, to make a kaleidoscope. Connect them together to make a prism. Place these mirrors in a circular cardboard tube or a tube made of thick chart paper. Assemble the tube such that it is slightly bigger than the mirror strips. Close one end of this tube with cardboard with a hole in the middle that you can see through. Put a piece of the transparent plastic sheet under the cardboard to make it more durable. Fix a round plate glass on the opposite end, touching the mirrors. Place numerous pieces of coloured glass on this glass plate (broken pieces of coloured bangles). A round glass plate is used to close this end of the tube. Make sure there’s enough space for the coloured pieces to move around. Now the kaleidoscope is ready to be used.

Question 19. Write any five ways to take care of your eyes.

Answer 19. Some common measures to take care of the eyes are as follows-

• Use suitable eyewear if advised.
• It is not good for the eyes to have too little or too much light. Eye strain and headaches are caused by insufficient light. The retina can be impaired by too much light, such as sunlight, a strong lamp, or a laser torch.
• Do not look directly at the sun or bright light.
• Do not rub your eyes. If dust particles enter your eyes, rinse them with clean water. If your condition does not improve, go to the doctor.
• Always read books at a comfortable distance for your eyes. Avoid reading the book too close to your eyes or keeping it too far away when reading.

Question 20. Suppose you are in a dark room. Can you see objects in the room? Can you see objects outside the room? Explain.

Answer 20. If a person is inside a room with no light, it is impossible to see the object inside the dark room, but the object outside the room is seen easily.

When light falls on the eyes after reflecting from the object, it becomes visible. If the room is dark, the objects in the room reflect no light. Hence, the person cannot see the objects in the room without light.

Question 21. Mention the following, whether regular or diffused reflection, which will occur when a light beam strikes. Justify your answer in each case.

(a) A Polished wooden table.

(b) Chalk powder.

(c) A Cardboard surface.

(d) A Marble floor with some water spread over it.

(e) A Mirror.

(f) A Piece of paper.

Answer 21. a) A wooden table that has been polished-regular reflection.

A surface polished recently is an example of a smooth surface. A wooden table that has been polished has a smooth surface.

b) White chalk powder used in school- diffused reflection

chalk powder spread over a surface is a good example of an irregular surface. Hence, it is rough. Therefore, the diffused reflection will appear from the chalk powder.

c) Cardboard surface- diffused reflection.

The cardboard surface is a type of irregular surface.Hence, the diffused reflection will occur from a cardboard surface.

d) Marble floor – regular reflection.

A marble floor can be a good example of a stable surface. Since water makes the ceramic shiny, , the reflections are regular occurrences on this surface.

e) Mirror- regular reflection

A mirror has a very smooth surface, giving a regular reflection.

f) Piece of paper- diffused reflection

Although a piece of paper looks smooth, it has many irregularities on its surface. Due to this, it will give a diffused reflection.

Question 22. State the laws of reflection.

Answer 22. The law of reflection states that

1. a) The angle of incidence and angle of reflection are always equal.
2. b) At the point of incidence, the incident ray, reflected ray, and normal to the reflective surface all lie in the same plane.

Question 23. Describe that the incident ray, the reflected ray, and the normal at the point of incidence lie in the same plane.

Answer 23. On a table, place a plane mirror normal to the plane of the table. Make a small hole in a piece of paper and hold it perpendicular to the table. Try this experiment in a dark room. Put one more piece of paper on the table to make contact with the mirror. Draw a perpendicular line to the mirror on the piece of paper on the table. Now beam light rays with the help of a torch will pass through the small hole so that the light beam hits the normal at the lower part of the mirror. The light rays from the hole incident on the mirror will reflect the ray of light. Looking at the paper on the table, we can simply show that the incident ray, normal ray, and reflected ray at the incidence point lie in the same plane.

Question 24. What will be the angle of incidence of a ray when the reflected ray is perpendicular to the incident ray?

Answer 24. If the reflected ray lies perpendicular to the incident ray, then the angle of incidence is 45 degrees. According to the laws of reflection, the incidence angle and the angle of reflection are equal. Hence, the incidence ray and angle of reflection are 90/2=45 degrees.

Question 25. How many images of the candle will be seen if it is placed between two parallel plane mirrors separated by a distance of 40 cm?

Answer 25. When a candle is placed between two parallel plane mirrors separated by 40 cm, multiple and infinite images will be seen due to the multiple reflections between the mirrors. An unlimited number of images are formed when two mirrors are placed parallel to each other.

Question 26. The part of the eye which controls the light entering is called –

(a) iris

(b) cornea

(c) lens

(d) retina

Answer 26. The answer is option (a) iris.

Explanation – Iris is a dark, muscular part behind the cornea. Its function is to regulate the entry of light.

Question 27. We can see a non-luminous object when light-

(a) completely passes through the object.

(b) gets completely absorbed by the object.

(c) emitted by the object falls on our eye.

(d) is reflected from the object towards the eye.

Answer 27. The answer is option (d) is reflected from the object towards the eye.

Question 28. A light ray incident on mirror A at an angle of 25 degrees falls on mirror B after reflection. The angle of reflection for the reflected ray from mirror B would be-

(a) 25 degrees.

(b) 50 degrees.

(c) 65 degrees. 

(d) 115 degrees.

Answer 28. The answer is option (c) 65 degrees.

Explanation- The angle of reflection for the ray reflected from mirror B will be 65° because the reflected ray from mirror A forms an incident ray on mirror 6 and is then reflected by an angle of 65°.

Question 29. Which statements are correct regarding rods and cones in the human eye?

(a) Cones are sensitive to dim light.

(b) Cones are sensitive to bright light.

(c) Rods are sensitive to bright light.

(d) Rods can sense colour.

Answer 29. The answer is option (b) Cones are sensitive to bright light.

Explanation- Cones are sensitive to bright light; hence, they sense colour, whereas rods are sensitive to dim light and cannot sense colour.

Question 30. Which part of the eye gives colour to our eyes?

Answer 30. Iris of the eye gives colour to the eyes.

Question 31.While waving his hand fastly in front of his eyes, Boojho observes that his fingers appear blurred. What could be the reason for it?

Answer 31. The persistence of vision is the reason for the blurred vision of Boojho; while waving his hand fastly in front of his eyes, he observes that his fingers appear blurred.

Question 32. How often is a ray of light reflected by two plane mirrors placed parallel and facing each other?

Answer 32. Two plane mirrors reflect an infinite number of times, a ray of light placed parallel and facing each other.

Question 33. The angle between the ray of incidence and the reflected ray is 60°. What is the angle of incidence?

Answer 33. The answer is 30°.

Explanation- The angle of reflection is equal to the angle of incidence.

Since, the Angle of incident ray+ Angle of reflected ray is 60°.

The angle of incidence = 30°

Question 34. What happens to the light when it gets dispersed? Give an example.

Answer 34. When the light gets dispersed, it gets split into its constituent colours. Ex: rainbow.

Question 35. The eyes of nocturnal animals have large corneas and large pupils. How does this structure help them?

Answer 35. They can see objects even in low light. A large pupil and a large cornea help lighter enter their eyes.

Question 36. What type of lens is found in our eyes? Where does it form the image of the object?

Answer 36. Our eyes have a convex lens, forming the image on the retina.

Question 37. Which part of the eye gets affected when someone suffers from a cataract? How is it treated?

Answer 37. If a person suffers from a cataract, their eye lens will become cloudy. Cataracts can be cured by replacing the opaque lens with an artificial lens.

Question 38. Explain the process which enables us to recognise motion in a cartoon film.

Answer 38.A Carton movie is a projection of a static picture. 24 pictures are shown in one second in a specific order, giving us the perception of movement.

Question 39. How is the phenomenon of light reflection used in making a kaleidoscope? What are the uses of a kaleidoscope?

Answer 39. The kaleidoscope gives several images formed by reflection from the mirrors inclined towards one another. Designers and artists use a kaleidoscope to get ideas for new patterns to design wallpapers, jewellery, and fabrics.

Question 40. What is a periscope? How many mirrors are there in a periscope?

Answer 40. A periscope is an instrument that reflects the reflected ray again. It is made of a tube attached to a set of mirrors. There are two mirrors in a periscope.

Question 41. State the various uses of a periscope.

Answer 41. Uses of periscope-

1. It is used to see over and around an object.
2. It is used to see over a wall.
3. Used in warfare.

Question 42. Can you see your image in a plane mirror? Write two characteristics of the image so formed.

Answer 42. Yes, we can see our image in a plane mirror. The image formed will be-

1. Virtual and erect.
2. The same size as the object

Question 43. Explain why a book lying on the table in a room can be seen from all  parts of the room.

Answer 43. A book lying on the table in a room can be seen from all parts of the room because of the light reflection falling on it.

Question 44. We can see the sun because it is glowing. How can we see the moon?

Answer 44. We see the moon because the light from the sun falls on the moon and is reflected on the earth.

Question 45. Write the two types of reflection of light. What kind of reflection makes us see an object from all directions?

Answer 45. The two types of light reflection are- regular reflection of light and diffuse reflection of light.

The regular reflection of light makes us see an object from all directions.

Question 46. A wall reflects light and a mirror also reflects light. What is the difference in the way they 

reflect light?

Answer 46. Reflection of light from the wall is a diffused reflection, and reflection of light from a mirror is a regular reflection.

Question 47. What are the main parts of the human eye?

Answer 47. The main parts of the human eye are-

Iris, Lens, Pupil, Cornea, Retina, Ciliary muscles, and Optic nerve.

Question 48. What is the vision range of a normal person?

Answer 48. A normal human eye’s vision range is from 25cm to infinity.

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Our question bank of Class 8 Science Chapter 16 Important Questions covers questions from different topics covered in the Light chapter.

Students can face difficulty understanding complex topics in Science. One way to resolve this is to practise Important Questions Class 8 Science Chapter 16. The question bank covers all the important topics, and these questions are created from an exam point of view and are most likely to be asked in the exam. Practising Important Questions Class 8 Science Chapter 16 gives students a competitive edge.

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• The solutions provide details required in clearing the question paper, which can benefit students during final exam preparation and their future career paths and achievements.

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