Light Class 8 Important Questions and Answers
Important questions of Class 8 Science Chapter 16 Light is given below. These important questions will help students while preparing for the exam. Practising these important questions will analyse their performance and work on their weak points. Score well in exam of Class 8 Science by going through these important questions. Students of Class 8 can download important questions of Class 8 Science Chapter 16 Light PDF by clicking the link provided below.
Important Questions of Class 8 Science Chapter 16 Light
Here you can get Class 8 Important Questions Science based on NCERT Text book for Class 8. Science Class 8 Important Questions are very helpful to score high marks in board exams. Here we have covered Important Questions on Light for Class 8 Science subject.
Very Short Answer Questions
1. What makes things visible?
Answer: Light.
2. Can you see an object in the dark?
Answer: No.
3. What is mirror?
Answer: A smooth and shiny surface is called a mirror.
4. What kind of image is formed by a plane mirror?
Answer: Virtual and erect image.
5. Where is the image formed by a plane mirror?
Answer: Behind the mirror.
6. Where does the image form in our eye?
Answer: At Retina.
7. Where is no image formed?
Answer: Blind spot.
8. For what time the image stays on the retina?
Answer: About 1/16th of a second.
9. Which bird is called night bird?
Answer: Owl is called night bird.
10. Which surface shows regular reflection?
Answer: Smooth or regular surface.
11. Which surface shows diffused reflection?
Answer: Rough or irregular surface.
12. What size of image formed in a plane mirror?
Answer: Same size of the object.
13. How many mirrors are used in Kaleidoscope?
Answer: Three mirrors.
14. How many colours are there in spectrum of light?
Answer: Seven colours.
15. How many colours are there in white light?
Answer: Seven colours.
16. What is the shape of human eye?
Answer: Spherical shape.
17. What is the front transparent parts of the eye called?
Answer: Cornea.
18. What is the small opening in the iris called?
Answer: Pupil.
19. Which part of eye is controlled by iris?
Answer: Pupil.
20. What is the coloured part of eye called?
Answer: Iris.
21. What is the function of iris?
Answer: Iris controls the amount of light entering into the eye through pupil.
22. Which part of the body sends the sensation felt to the brain?
Answer: Nerve cells.
23. How many kinds of nerve cells are there in the retina?
Answer: Two (cones and rods).
24. Which cells of the retina are sensitive to bright light and colour?
Answer: Cones.
25. Which cells of retina are sensitive to dim light?
Answer: Rods.
26. What is the distinct vision of normal eye?
Answer: 25 cm.
27. Who invented the system of reading for blind man?
Answer: Braille.
Short Answer Type Questions
1: Define light. Discuss its importance.
Answer: Light is an electromagnetic radiation that is visible to the human eye, and is responsible for the sense of sight. Visible light has a wavelength in the range of about 380 nanometres to about 740 nm between the invisible infrared.
2: Why we are not able to see any object in the dark?
Answer: We can see any object when light reflected by that object reaches our eyes, but in dark room no light is reflected by the object thus we are not able to see in the dark.
3: Why the image formed by concave mirror is sometimes real, while sometimes virtual?
Answer: In case of concave mirror the image depends upon the distance of the object from the mirror. If the object is beyond the focus then real image is formed and if the object is closer than the focus then virtual image is formed
4: Why convex mirrors are used in vehicles?
Answer: Convex mirrors are used in vehicles because the image formed by convex mirror is always erect and smaller in size.
5: Explain the two laws of reflection.
Answer: There are two laws of reflection: the angle of incidence is equal to the angle of reflection and incident rays, reflected rays and normal rays drawn at the point of incidence to the reflecting surface lies in the same plane.
6: What kind of image is formed by a plane mirror?
Answer: Image formed by plane mirror is virtual, upright and of the same shape and size as of the object.
7: What do you mean by lateral inversion?
Answer: Lateral inversion is the reversal experienced by the image formed in a flat mirror. Although the image is the correct way up, its left and right sides are transposed.
8: “Reflected light can be reflected again”. Give an example to justify this statement.
Answer: Sit in front of a mirror, tell your friend to hold a mirror behind you to see your hair cut, your hair image will be shown in the mirror in front of you, this is the best example of reflected light can be reflected again.
9: Explain all parts of a human eye.
Answer: The eye has roughly spherical surface. The outer coat of eyes is white and tough to protect the interior of eyes from any kind of accident. Its transparent front part is called cornea, behind the cornea there is a dark muscular structure called iris. In the iris there is small opening called pupil. The size of the pupil is controlled by the iris, the iris control the amount of light entering into the eye.
10: Explain the function of retina of eyes.
Answer: The lens focuses light on the retina which contains several nerve cells. Sensations felt by the nerve cells are then transmitted to brain through the optic nerve.
11: Why blind spot is named so?
Answer: At the junction of the optic nerve and the retina, there are no sensory cells, so there is no possibility of vision at that spot, thus it is called blind spot.
12: What is the function of eyelids?
Answer: Eyelids prevent any object from entering the eye, eyelids also shut out light when not required.
13: What is myopia? How it can be corrected?
Answer: Myopia is a vision condition in which close objects are seen clearly, but objects farther away appear blurred. Most commonly myopia can be corrected through the use of corrective lenses, such as glasses or contact lenses. It may also be corrected by refractive surgery, though there are cases of associated side effects. The corrective lenses have a negative optical power (i.e. are concave)
14: What is hyper myopia? How it can be corrected?
Answer: Hypermetropia means long sight and is where the image of a nearby object is formed behind the retina. This could be because the eye is too short, or the cornea or crystalline lens does not refract the light enough. A hypermetropic person may have blurred vision when looking at objects close to them, and clearer vision when looking at objects in the distance. By placing a convex (plus powered) lens in front of a hypermetropic eye, the image is moved forward and focuses correctly on the retina.
15: Why eyesight becomes foggy in old age?
Answer: In old age eyes eye lens becomes cloudy, and person develops a cataract that is loss of vision. This defect can be treated by replacing opaque lens with a new artificial lens.
16: How cataract disorder can be corrected?
Answer: In old age eyes eye lens becomes cloudy, and person develops a cataract that is loss of vision. This defect can be treated by replacing opaque lens with a new artificial lens.
17: Give some possible measures to take care of the eyes.
Answer: Some possible measures are as follows:
1. If advised use suitable spectacles
2. Avoid too much or too little eyes
3. Do not look at the sun or a powerful light directly
4. Never rub your eyes
5. Wash your eyes properly and frequently with water
6. Always read at the normal distance for vision.
18: What is the braille system?
Answer: Braille is a writing system which enables blind and partially sighted people to read and write through touch. It was invented by Louis Braille.
19: Why owl can see very well in the night but not during the day like other animals?
Answer: The owl has a large cornea and a large pupil to allow more light into the eye. It has large number of rods on its retina and few cones that enables it to see properly in dim light or in dark.
20: Differentiate between regular and irregular reflection. Does irregular reflection mean the failure of the laws of reflection?
Answer:
| Regular reflection | Diffused reflection |
| (i) It takes place from a smooth or regular surface (ii) Here all reflected rays are parallel to each other (iii) Reflected rays go in one direction. | (i) It takes place from a rough surface (ii) Here all reflected rays are not parallel to each other (iii)Reflected rays are scattered in different direction. |
In diffused reflection each ray obeys the law of reflection, thus there is no failure of law of reflection.
21: Mention whether diffused or regular reflection will take place when :
- A beam of light strikes a mirror
- A beam of light strikes a cardboard surface.
- A beam of light strikes a piece of paper. To the incident ray
Answer:
- Regular reflection because mirror has smooth surface
- Diffused reflection because cardboard has irregular surface.
- Diffused reflection, because a piece of paper appears smooth but it has lot of minor irregularities.
22: Give an important characteristic of a normal eye.
Answer: Normal eye can clearly see distant objects as well as object nearby.
23: What is reflection?
Answer: When rays of light return at some angle by striking a smooth surface, this phenomenon is called reflection of light.
24: What is incident ray?
Answer: The light ray, which strikes any surface is called the incident ray.
25: What is reflected ray?
Answer: The ray that comes back from the surface after reflection is known as the reflected ray.
26: Define normal.
Answer: A perpendicular line on the mirror at the point where incident ray strikes is called normal.
27: Define angle of incidence.
Answer: The angle between the normal and incident ray is called the angle of incidence.
28: Define angle of reflection.
Answer: The angle between the normal and reflected ray is called angle of reflection.
29: Write the laws of reflection.
Answer: There are two laws of reflection.
(i) Angle of incidence is equal to angle of reflection.
(ii) Incident ray, reflected ray and normal at the point of incidence, all lie in the same plane.
30: What is lateral inversion?
Answer: When an image is formed by a mirror the left of the object appears on the right and the right appears on the left, this is known as lateral inversion.
31: What do you mean by diffused or irregular reflection?
Answer: When all the parallel rays reflected from a plane surface are not parallel, the reflection is known as diffused or irregular reflection.
32: Define regular reflection.
Answer: When reflected rays from a smooth surface are parallel, it is known as regular reflection.
33: What do you mean by multiple images?
Answer: When two mirrors are kept parallel to each other then numerous images of an object are seen in these mirrors. This is known as multiple images.
34: What is the use of kaleidoscope?
Answer: Designers of wallpapers, fabrics, artists use kaleidoscope to get ideas for new patterns.
35: Define dispersion of light.
Answer: Splitting of light into its seven colours is known as dispersion of light.
36: Give an example of natural dispersion.
Answer: Rainbow is a natural phenomenon showing dispersion.
37: What is the function of rods and cones in our eye?
Answer: Cones are sensitive to bright light and colour whereas rods are sensitive to dim light.
38: What is blind spot?
Answer: At the junction of the optic nerve and retina, there are no sensory cells, so no vision is possible at the spot. This is called the blind spot.
39: What is the function of eyelids.
Answer: Eyelids prevent any object from entering the eye. They also shut out light when not required.
40: What is the Braille system?
Answer: Louis Braille developed a system for visually challenged persons. This is known as Braille system. He developed Braille code for common languages.
41: How many images of a mobile will be formed if it is placed between two parallel plane mirrors separated by 30 cm?
Answer: Infinite number of images will be formed if it is placed between two parallel plane mirrors.
Long Answer Type Questions
1. What is reflection of light? State the laws of reflection.
Answer: Reflection is a phenomenon in which a beam of light falls on some surface and returns back in different directions. It may be regular or irregular.
Following are the laws of reflection:
(i) When a ray of light falls on a reflecting surface it is reflected back in such a way that the angle of incidence is equal to the angle of reflection, i.e. ∠i = ∠r.
(ii) The incident ray, the normal and the reflected ray, all lie in the same plane.
2. What are the characteristics of image formed by plane mirror?
Answer: Characteristics of image formed by a plane mirror are:
(i) Plane mirror forms virtual images.
(ii) Plane mirror forms erect images.
(iii) Image is laterally inverted.
(iv) Image formed is of the same size as the object.
(v) The distance of image from the mirror is equal to the distance of object from the mirror.
3. How will you prove that the angle of incidence is equal to the angle of reflection.
Answer: Draw lines showing the position of the plane mirror, the incident ray and the reflected ray on the paper with the help of your friends. Remove the mirror. Draw a line making an angle of 90º to the line representing the mirror at the point where the incident ray strikes the mirror. This line is known as the normal. The angle between the normal and incident ray is called the angle of incidence (∠i). The angle between the normal and the reflected ray is known as the angle of reflection (∠r). Measure the angle of incidence and the angle of reflection. Repeat the activity several times by changing the angle of incidence. You will see that at every time the angle of incidence is equal to the angle of reflection. This proves that the angle of incidence is equal to the angle of reflection.
4. Explain the structure and working of a human eye.
Answer: The eye has a roughly spherical shape. The outer coat of the eye is white. It is tough so that it can protect the interior of the eye from accident. Its transparent front part is called cornea. Behind the cornea, we find a dark muscular structure called iris. In the iris, there is a small opening called pupil. The size of the pupil is controlled by the iris. The iris controls the amount of light entering into the eye. Behind the pupil of the eye is a lens which is thicker at the centre. The lens focuses light on the retina. The retina contains several nerve cells. Sensations felt by the nerve cells are then transmitted to the brain through the optic nerves. There are two kinds of cells; cones and rods.
5. What is Braille system? Explain.
Answer: Braille is a method of writing for visually challenged person. This system was invented by Louis Braille in 1821 and adopted in 1932. He was also a blind person. In this method text is written on a thick paper using special symbols representing the letters of alphabet. Groups of dots are employed to write letters. There is Braille code for common languages, Mathematics and Scientific notation. Braille system has 63 dots patterns. Each pattern represents a letter, a combination of letters, a common word or a grammatical sign. Dots are arranged in cells of two vertical rows of three dots each. Codes of music and mathematics are different. Any language can be read through the codes of Braille.
