Light Class 8 Extra Questions Science Chapter 16

Light Class 8 Extra Questions Science Chapter 16

Light Class 8 Extra Questions Very Short Answer Questions

Light Class 8 Extra Questions And Answers Question 1.
Why fingers appear blurred when we move our hand very fast in front of our eyes?
Answer:
This is due to persistence of vision l/16th of a second.

Class 8 Light Extra Questions Question 2.
What makes things visible?
Answer:
When light reaches our eyes after striking an object, we are able to see an object.

Class 8 Science Chapter 16 Extra Questions Question 3.
Which element is used at the back of plane mirror?
Answer:
Silver

Class 8 Science Chapter Light Extra Questions Question 4.
The distance between the object and its image formed by a plane mirror appears to be 18 cm. What is the distance between mirror and the object?
Answer:
9 cm

Name The Phenomenon Shown In The Figure Class 8 Question 5.
How is hypermetropia corrected?
Answer:
It is corrected by using convex lens.

Class 8 Science Light Extra Questions Question 6.
How is myopia corrected?
Answer:
It is corrected by using concave lens.

Class 8 Science Ch 16 Extra Questions Question 7.
A ray of light is incident on a mirror at an angle of 40°. What is the angle of reflect! u?
Answer:
40°

Class 8 Science Chapter 1 Extra Questions And Answers Question 8.
Name a device which works on the principle of multiple reflection.
Answer:
Periscope

Extra Questions For Class 8 Science With Answers Question 9.
Can we see an object in the dark?
Answer:
No

Question 10.
What is the nature of the image formed by the plane mirror?
Answer:
Virtual and erect

Question 11.
Where is the image formed in a plane mirror?
Answer:
Behind the mirror

Question 12.
The angle between the incident ray and reflected ray is 100°. What is the value of angle of incidence?
Answer:
∠i + ∠r = 100°
Since, ∠i = ∠r
∴ ∠i + ∠i = 100°
⇒ 2 ∠i = 100°
⇒ ∠i = \(\frac{100^{\circ}}{2}\) = 50
∴ Angle of incidence = 50°.

Question 13.
What is yellow spot?
Answer:
It is highly light sensitive spot for seeing things with highest clearness.

Question 14.
Give an example of night bird.
Answer:
Owl

Question 15.
What do we call the image that cannot be obtained on a screen?
Answer:
Virtual

Question 16.
Show mathematically, the first law of reflection.
Answer:
∠i = ∠r

Question 17.
Name the phenomenon shown in the figure.
Answer:
Lateral inversion.

Question 18.
Express the mathematical formula to calculate the number of images formed when two mirrors are inclined at θ angle.
Answer:
Number of images = \(\frac{360^{\circ}}{\text { Angle }(\theta)}\) – 1.

Question 19.
How many colours are there in a spectrum of white light?
Answer:
Seven

Question 20.
Name the scientist who studied that if a white light is passed through a prism, it splits into different colours.
Answer:
Sir Issac Newton

Question 21.
Name the spot inside the human eye where the image is not visible.
Answer:
Blind spot

Question 22.
Name the liquid found between the cornea and lens.
Answer:
Aqueous humour

Question 23.
Name the liquid found between the lens and the retina.
Answer:
Vitreous humour

Question 24.
Define the incident ray.
Answer:
The ray of light striking the surface is called an incident ray.

Question 25.
Define angle of reflection.
Answer:
The angle between the reflected ray and the normal is called the angle of reflection.

Light Class 8 Extra Questions Short Answer Questions

Question 1.
Define light.
Answer:
Light is defined as a form of energy that stimulates sight and makes things visible.

Question 2.
What is reflection?
Answer:
The bouncing back of light into the same medium after it falls on a surface is called reflection.

Question 3.
What is a mirror?
Answer:
A piece of glass with a shiny metal-covered at back, that reflects light, producing an image of the object in front of it is known as mirror.

Question 4.
State the two laws of reflection.
Answer:
The two laws of reflection are:

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

Question 5.
How do we see various objects?
Answer:
We see various objects due to reflection. As we know all surface reflect light, when light falls on any object, it reflects the light. The reflected light reaches our eyes and we are able to see the object.

Question 6.
What do you mean by reflected ray?
Answer:
The ray of light which is returned back into the same medium after the incident ray strikes the surface ’ is called reflected ray.

Question 7.
What is irregular reflection?
Answer:
Irregular reflection is defined as the reflection of light from an uneven surface. In irregular reflection, the reflected beam is not parallel.

Question 8.
List the characteristics of an image formed in a plane mirror.
Answer:
he characteristics of an image formed in a plane mirror are:

• It is virtual.
• It is erect.
• It is of same size as the object.

Question 9.
What is lateral inversion?
Answer:
The phenomenon of changing left side to right and right side to left by the mirror while forming image is called lateral inversion.

Question 10.
What is the far point and near point of the human eye with normal vision?
Answer:
In optics, the farthest and closest point at which an object can be brought into focus by the eye are called far point and near point of the eye respectively. The far point of the human eye with normal vision is infinity. The near point of the human eye with normal vision is 25 cm.

Question 11.
What is aqueous humour?
Answer:
The space between the cornea and lens is filled with a liquid called the aqueous humour.

Question 12.
Differentiate between rod and cone cells.
Answer:
Rods are the rod-shaped cells present in the retina of an eye which are sensitive to dim light whereas cones are the cone-shaped cells present in the retina of the eye which are sensitive to bright light.

Light Class 8 Extra Questions Long Answer Questions

Question 1.
Write a short note on Braille system.
Answer:
The most popular resource for visually challenged persons is Braille. Braille system was developed by Louis Braille. He himself was a visually challenged person. There is Braille code for common languages, mathematics and scientific notation. Many Indian languages can be read using the Braille system.

Braille system has 63 dot patterns or characters. Each character 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. Patterns of dots to represent some English letters and some common words are shown in Fig. 16.26.

These patterns when embossed on Braille sheets help visually challenged persons to recognise words by touching. To make them easier to touch, the dots are raised slightly.

Visually challenged people learn the Braille system by beginning with letters, then special characters and letter combinations. Methods depend upon recognition by touching. Each character has to be memorised. Braille texts can be produced by hand or by machine. Typewriter-like devices and printing machines have now been developed.

Question 2.
Explain the phenomenon of dispersion of light.
Answer:
Dispersion is defined as the phenomenon of splitting of white light into different colours on passing through a transparent medium such as prism. When white light is passed through a prism, it splits into seven colours. It is observed that the colours are in the following order:
Violet (V), Indigo (I), Blue (B), Green (G), Yellow (Y), Orange (O) and Red (R).
The order of colours can be remembered by the acronym VIBGYOR. This coloured band is called spectrum of white light.

Question 3.
Write a note on ‘The Human Eye’.
Answer:
Eye ia a sense organ that enables us to see the world around us. It is roughly spherical in shape.

• The first part that is bulged outward is called ‘cornea. It protects the eye.
• Behind the cornea, the coloured part of the eye, iris is present. It controls the size of the pupil.
• Pupil is a small opening in the cornea which allows the light to enter the eye.
• Behind the iris, eye lens is present which is a convex lens. It focus the image on retina, by bending the light rays.
• Retina is the inner back surface of the eye which acts as a screen to form image. It is sensitive to light.
• The sensation of the image formed on the retina is carried to the brain by the optic nerve.
• Optic nerve is connection between the eye and the

Question 4.
Write the ways to protect your eyes.
Answer:
Eyes are very delicate organ that enable us to see this colourful world. Thus, we must protect our eyes and take proper care of them.
Following are the ways to protect the eye:

• Always sit straight while reading or writing.
• Never read while walking or lying down.
• Wash your eyes frequently with clean water.
• Never read in the dim or too much bright light.
• Never rub your eyes with hands.
• Never bring the book too close to your eyes.
• Eat foods rich in vitamin A.

Question 5.
Explain some common eye defects in human.
Answer:
Some eye diseases are:

(i) Cataract: A cataract is a clouding of the lens in the eye leading to a decrease in vision. It can affect one or both eyes. Often it develops slowly. Symptoms may include faded colours, blurry vision, halos around light, trouble with bright lights, and trouble seeing at night. This may result in trouble driving, reading, or recognising faces. Cataracts are the cause of half of blindness and 33% of visual impairment worldwide. Cataract is treated by replacing the opaque lens with a new artificial lens.

(ii) Myopia: Near-sightedness or myopia, is the most common refractive error of the eye. Myopia occurs when the eyeball is too long, relative to the focusing power of the cornea and lens of the eye. This causes light rays to focus at a point in front of the retina, rather than directly on its surface. It can be corrected using spectacles made of concave lens.

(iii) Hypermetropia: Hypermetropia or long-sightedness occurs when eyeball is too short or the cornea or crystalline lens does not refract the light enough. This lead to formation of the image of a nearby object behind the retina. 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.

(iv) Astigmatism: It is a defect in the eye or in a lens caused by a deviation from spherical curvature, which results in distorted images, as light rays are prevented from meeting at a common focus. It can be corrected by using a convex lens or concave lens or both.

Light Class 8 Extra Questions Higher Order Thinking Skills

Question 1.
What is power of accommodation?
Answer:
The process by which the ciliary muscles change the focal length of an eye lens to focus distant or near objects clearly on the retina is called power of accommodation.

Question 2.
How does large cornea and a large pupil in the eyes of the nocturnal birds help them?
Answer:
Large cornea and a large pupil allow more light to enter their eyes and they can see objects even in faint light.

Question 3.
What kind of lens is there in our eyes? Where does it form the image of an object?
Answer:
Convex lens is there in our eyes. It forms image of an object on the retina.

Question 4.
Boojho planned an activity to observe an object A through pipes as shown in the given figure, so that he could see objects which he could not directly see.

(a) How many mirrors should he use to see the object?
(b) Indicate the positions of the mirrors in the figure.
(c) What must be the angle with respect to the incident light at which he should place the mirrors?
(d) Indicate the direction of rays in the figure.
(e) If any of the mirrors is removed, will he be able to see the object?
Answer:
(a) Three

(c) 45°

(e) No, he will not be able to see the object.

Light Class 8 Extra Questions Value-Based Questions

Question 1.
While playing, something entered into Somya’s eye. She immediately washed her eye with cold water. But as the irritation persisted, she immediately reported to her class teacher. Her class teacher took her to an eye doctor.

• What should be done if some foreign particles enter your eyes?
• Why is it not advised to rub your eyes when there is an eye irritation due to foreign particles?
• Do you think Somya was right in her action?
• What value of Somya is seen here?

Answer:

• We must do the following things:
  • Restrict eye movement
  • Shut the eyelid
  • Do not rub eyes
  • Try to clean it with splash of clear water
  • Contact eye doctor immediately.
• Foreign object may cause abrasions or scratches on our cornea or rubbing. It may also cause bleeding of cornea.
• Yes.
• She is intelligent, knowledgeable and aware of such kind of small accidents.

Activities and Project
Question 1.
Make your own mirror. Take a glass strip or glass slab, clean it and put it on a white sheet of paper. See yourself in the glass. Next put the glass slab on a black sheet of paper. Again look into the glass. In which case do you see yourself better and why?
Answer:
We can see ourselves better in the case we put the glass slab on white paper because white sheet reflects more light as compared to black sheet.

Question 2.
Make friends with some visually challenged students. Enquire from them how they read and write. Also find out how they are able to recognise objects, hurdles and currency notes.
Answer:
Do it yourself.

Question 3.
Meet an eye specialist. Get your eye sight checked and discuss how to take care of your eyes.
Answer:
We can take care of our eyes by:

• regular check up.
• avoiding study in very dim light.
• proper sitting and reading posture.
• washing eyes daily.

Question 4.
Survey your neighbourhood. Find out how many children below the age of 12 years use spectacles. Find out from their parents what, in their view, could be the reason for the weak eyesight of their children.
Answer:
Do it yourself.

I. Multiple Choice Questions (MCQs)
Choose the correct option.
Question 1.
We are able to see an object due to the presence of
(a) light
(b) dark
(c) refraction
(d) object

Question 2.
The bouncing back of light into the same medium is called
(a) refraction
(b) reflection
(c) dispersion
(d) diffraction

Question 3.
A mirror has _________ surface.
(a) rough
(b) polished
(c) dark
(d) all of these

Question 4.
Maximum part of light is reflected by
(a) opaque object
(b) translucent object
(c) transparent object
(d) all of these

Question 5.
Beam of light striking the reflecting surface is ca
(a) incident ray
(b) reflected ray
(c) refracted ray
(d) normal ray

Question 6.
The back side of a plane mirror contains
(a) gold coating
(b) silver coating
(c) aluminium coating
(d) copper coating

Question 7.
The perpendicular drawn to the reflecting surface is called
(a) normal
(b) incident ray
(c) reflected ray
(d) none of these

Question 8.
There are _________ laws of reflection.
(a) one
(b) two
(c) three
(d) four

Question 9.
The angle of incidence is always ________ to theangle of reflection.
(a) greater
(b) smaller
(c) equal
(d) none of these

Question 10.
The angle between the reflected ray and the nor
(a) angle of incidence
(b) reflected ray
(c) angle of reflection
(d) point of incidence

Question 11.
The reflection of light from a smooth surface is called
(a) diffused reflection
(b) regular reflection
(c) dispersion
(d) spectrum

Question 12.
Which of the following results in diffused reflection?
(a) Plane mirror
(b) Shiny surface
(c) Silver
(d) Wood

Question 13.
The nature of image formed by plane mirror is
(a) real and inverted
(b) virtual and erect
(c) real and erect
(d) virtual and inverted

Question 14.
If you hold a pen in your right hand and stand in front of the mirror, the pen will be in the left hand in the image. This phenomenon is called
(a) lateral inversion
(b) diffraction
(c) reflection
(d) inversion

Question 15.
If two plane mirrors are inclined at an angle of 40°, number of images formed will be
(a) 7
(b) 8
(c) 9
(d) 5

Question 16.
Type of mirror used as side view mirror is
(a) convex mirror
(b) plane mirror
(c) concave mirror
(d) ground mirror

Question 17.
Band of seven colours is called
(a) VIBGYOR
(b) dispersion
(c) spectrum
(d) reflection

Question 18.
Front bulged part of the eyeball is called
(a) cornea
(b) iris
(c) retina
(d) pupli
(c) 65
(d) 115

Question 19.
Two mirrors A and B are placed at right angles to each other. A ray of light incident on mirror A at an angle of 25° falls on mirror B after reflection. The angle of reflection for the ray reflected from mirror B would be
(a) 25°
(b) 50°
(c) 65°
(d) 115°

Question 20.
Visually impaired people can read and write using
(a) electronic writer
(b) Braille system
(c) digital pens
(d) hearing aids
Answer:
1. (a)
2. (b)
3. (b)
4. (a)
5. (a)
6. (b)
7. (a)
8. (b)
9. (c)
10. (c)
11. (b)
12. (d)
13. (b)
14. (a)
15. (b)
16. (a)
17. (c)
18. (a)
19. (c)
20. (b)

II. Fill in the Blanks
Fill in the blanks with suitable word/s.
1. Light is a form of ___________.
2. The ray of light which strikes the reflecting surface is called ___________.
3. The bouncing back of light after it falls on a surface is called ___________.
4. A mirror has ___________ and ___________ surface.
5. ___________ is the perpendicular line on the incidence point.
6. A plane mirror forms a ___________ image.
7. The ray which returns after striking the surface is called ___________ ray.
8. Angle of incidence is always ___________ to the angle of reflection.
9. Reflection from a smooth surface is called ___________ reflection.
10. The size of image formed by the plane mirror is ___________ as size of object.
11. Splitting of light into seven colours is called ___________.
12. Kaleidoscope is based on the concepts of ___________.
13. The point on the surface at which incident ray strikes is called ___________.
14. The reflection of light from an uneven surface is called ___________.
15. Paper is a ___________ surface.
16. Mirror is a ___________ surface.
17. When the mirrors are inclined at 90°, we get ___________ images.
18. In bright light, the size of pupil ___________.
19. The space between the cornea and lens is filled with a liquid called ___________.
20. Braille system was invented by ___________.
Answer:
1. energy
2. incident
3. reflection
4. smooth, polished
5. Normal
6. virtual
7. reflected
8. equal
9. regular
10. same
11. dispersion
12. multiple reflection
13. point of incidence
14. diffused reflection
15. rough
16. smooth
17. three
18. decreases
19. aqueous humour
20. Louis Braille

III. Match the following
Match the items given in column I suitably with those given in column II.

Answer:
1. (b)
2. (c)
3. (a)
4. (g)
5. (j)
6. (h)
7. (e)
8. (l)
9. (f)
0. (k)
11. (i)
12. (d)
13. (o)
14. (m)
15. (n)

IV. True or False
State whether the given statements are true or false.
1. Deficiency of vitamin B causes night blindness.
2. In the Braille system, patterns are made with coloured dots.
3. Normal make 60° angle with the reflecting surface.
4. Angle of incidence is always equal to angle of reflection.
5. Diffused reflection occurs due to rough surface.
6. Kaleidoscope is based on the principle of dispersion of light.
7. Both incident ray and reflected ray lie in the same plane.
8. The choroid prevents the internal reflection of light and protects the light sensitive inner parts of the eye.
9. Rainbow forms due to dispersion.
10. Rods are sensitive to bright light.
11. The iris is the coloured part of the eye.
12. Diffused reflection is due to the failure of laws of reflection.
13. Ciliary muscles changes the shape of the lens in the eye.
14. We should not wash our eyes.
15. Braille was designed by Louis Braille.
Answer:
1. False
2. False
3. False
4. True
5. True
6. False
7. True
8. True
9. True
10. False
11. True
12. False
13. True
14. False
15. True

Extra Questions for Class 8 Science