Lakhmir Singh Manjit Kaur Class 8 Science 16th Chapter Light

Lakhmir Singh Manjit Kaur Class 8 Science 16th Chapter Light Solutions

Lakhmir Singh and Manjit Kaur Science solution: Light Chapter 16. Get easy solutions of Lakhmir Singh and Manjit Kaur Science solution Chapter 16 . Here we have given Chapter 16 all solution of Class 8. Its help you to complete your homework.

• Board – CBSE
• Text Book – SCIENCE
• Class – 8
• Chapter – 16

VERY SHORT ANSWER TYPE QUESTIONS answer

1) The ray of light which falls on the mirror surface is called incident ray.

2) The ray of light which is sent back by the mirror is called reflected ray.

3) Equal.

4) The point at which the Incident ray strikes the mirror is called the point of incidence.

5) Imaginary line.

6) The angle between incident ray and normal is called the angle of incident.

7) The angle between reflected ray and normal is called the angle of reflection.

8) 30

9) 19

10) The light will go straight.

11) 0⁰

12) 0⁰

13) 45⁰

14) ‘Ray-box’

15) (a) irregular surface.

(b) regular surface.

16) Regular reflection.

17) a> Diffuse reflection. b> Regular reflection.

18) 15 c.m.

19) Virtual.

20) Lateral inversion.

21) Periscope.

22)  a> parallal. b>  45

23) Infinite.

24) Kaleidoscope.

25) Kaleidoscope are used by designers of wall papers and fabrics.

26) Glass prism.

27) Seven color is formed.

28) convex.

29) 25 cm

30) Blind spot.

31) light.

32) night blindness.

33) Cornia.

34) Pupil.

35) Iris.

36) Cornia, Iris, Eye lense.

37) Large.

38) small.

39) a> True,  b> False, c>True.

40)  a> incidence, b> 2, c> Left; Left hand, d> Large. e>fewer, f> 1∕16, g>16, h> 24

SHORT ANSWER TYPE QUESTIONS Answer

41)   No, we cannot see the objects in a dark room.

If there is a light outside the room, then we can watch the objects outside the room.

When light reflects from a object in our eyes then we can see the objects. If there is no reflects of light from any objects then we cannot see any kind of objects.

42)  When light reflects from a object in our eyes then we can see the objects. If there is no reflects of light from any objects then we cannot see any kind of objects.

(a) We can not see a book which is placed behind a wooden screen this is because, wooden screen is a opaque material through which light cant not penetrate. That’s why we are unable to the book.

(b) We can not see the book in dark room, this is because book is a non luminous object. The non luminous object can be seen only when light coming from a luminous object falls on them.

43) We are able to see the moon because of the light that it receives from the sun when it revolves around our planet and without the presence of the light of the  sun then we cannot see the moon.

44) regular reflection and diffuse reflection.

Regular reflection makes us to see an object from all direction.

45) The wall have diffuse reflection and the mirror have regular reflection.

46) It is because the light in this room is reflects all the side from the book. That’s why a book lying on the table in a room can be seen from all the parts or the rooms.

47) <i belongs to angle of incidence and <r belong to angle of reflection.

The relation between them are –

(a) The <i and <r and the normal all lie in the same plane.

(b) <i is equal to the <r

48) The two characteristic are :

• The left side of an object appears on the right side in the image whereas the right side of object appears on the left side of the image. This is also known as lateral inversion.
• The image in a plane mirror is behind the mirror.

49) A periscope is a long, tubular device through which a person can see objects that are out of the direct line of sight.

There are two plane mirror in periscope.

50) The various uses of periscope are :

• A periscope is used to see over the heads of a crowd.
• A periscope is used by soldiers sitting in a trench.
• A periscope is used by a navy officer.

51) After giving the hair cut, hair dresser holds a small plane mirror behind the head. The light coming from Back of head is reflected by this small mirror to the big mirror, and the big mirror reflect the ‘reflected light’ again. So the person can watch the back hair of his head.

52) a> 2 , b> 7 , c> 1 , d> 5 , e> 3

(Rule to find No. of Images = (360 Degree ÷ x) – 1

53) Infinite.

54) Infinite number of Images.

55) Because the reflection of light.

56) When a white light go through a prism, it will be divide into seven colors.

57) The information we got about sunlight that white light consist of seven colors.

58) The process of splitting of white light into seven colors is called dispersion of light.

The natural phenomenon is – Rainbow.

59) Three long and narrow strips mirror in a kaleidoscope.

Kaleidoscope consists of three long and narrow strips of plane mirrors inclined at 60 degree to one another forming a hollow prism, an fitted into a  cardboard tube. One end of the cardboard tube is closed by an opaque disc having a small hole in its centre. The other end of the cardboard tube is closed with two circular disc of glass. The inner disc being of transparent glass and the outer disc of translucent glass. A number of different color plastics having different shapes are kept between the two glasses.

60)  By the focusing to the nearby objects, eye adjust itself to deal with light of varying intensity.

61) We cannot see our surrounding clearly when we enter a darkened cinema hall because then our pupil size is small so we cannot receive more light, but after few time, our pupil size increase so we can receive more light from surrounding.

62) The original eye lens can adjust its focal length by the help of eye muscles. But the ordinary convex lens made by the glass cannot adjust its focal length. This is the difference between eye lens and the ordinary convex lens made of glass.

63) a> Iris

b) Ciliary muscles converges light rays to form an image.

c) On Retina image is formed.

d) The optic nerves carries nerve impulse to the brain.

e) Ciliary muscles.

64) a> Cones , b> Rods. C> Cones

65) Rode are the rod-shaped cells and cones are the cone-shaped cells present in retina.

66) Myopia.

It is corrected by using spectacles containing concave lenses.

67) The medical condition in which the lens of eye of a person becomes progressively cloudy resulting in blurred vision is called cataract.

68) The persistence of vision means retention of a visual image for a short period of time after the removal of the stimulus that produced it the phenomenon that produces the illusion of movement when viewing motion pictures.

69) Care of our eyes :

• Wash our eyes at least twice a day with clean water.
• Always read by keeping the book at normal distance.
• Protect our eyes from injuries.

70)  if it happens, we need to splash our eyes with a lot of clean water.

71) Carrot, Cod-liver oil, green vegetables, eggs etc.

72) Because it puts strain on the eyes and may cause headache.

73) An owl’s eye have more rode cells in retina than the eagle. That’s why owl can see well in the night.

74) The blind spot is a small area of the retina insensitive to light where the optic nerve leaves the eye.

75) The changes of sides of an object and its mirror image is called lateral inversion.

LONG ANSWER TYPE QUESTIONS Answer

76) (a) The object which emit their own light are called luminous objects. Example : The sun, The lighted electric bulb.

(b) The objects which do not emit their own light are called non-luminous object. Example :  The moon, The earth.

77) (a) The difference is regular reflection of light from a smooth surface but the diffuse reflection of light from a rough surface.

Mirror produce regular reflection of light, a sheet of paper produce diffuse reflection of light.

(c) Polished Wooden Table – Regular.

Chalk Powder – Diffuse.

Cardboard – Diffuse.

Mirror – Regular (Plane Mirror)

Paper – Regular

Marble floor with water spread over it – Regular

(78) (a)

(b) The laws of the reflection are below –

i) The Incidence Ray (<i), The Reflected Ray (<r) & the Normal all lie on the same plane.

ii) The angle of incidence is equal to the angle of reflection i.e. <i = <r

79) (b) The various characteristics of the image formed in a plane mirror are following –

i) Virtual image is formed.

ii) The image is behind the mirror.

iii) The image is the same distance behind the mirror as the object is in front of it.

iv) Erect image is formed.

v) The image formed in a mirror is laterally inverted. That means when we rise our left it look like right.

80) (a)

(b) The function of the parts of the eye are point out below –

(a) Iris – It controls the amount of light entering the eye by adjusting the size of the pupils.

(b) Eye-lens – Its allows light to pass through them.

(c) Ciliary-muscles – It can change the curvature of eye lens make it thin or thick according to the need of the eye.

(d) Retina – Retina is a screen on which the image is formed.

(e) Optic Nerve – It send the message from the eye to the brain.

Higher Order Thinking Skills (HOTS)

101)

In a plane mirror the object and its image always remain at the same distance from the mirror. If a person stands 10 m from a large plane mirror then his distance from his image will be 20 m. So for him to be at 5 m from his image he has to be 2.5 m from the mirror. So he has to walk 7.5 m to be at 5 m distance from his image.

102)

According to the second law of reflection the angle of reflection is always equal to the angle of incidence. In this case the angle of incidence on XY mirror is 65 degree so the angle reflection will be also 65 degree. Now the reflected ray of XY mirror is the incident ray of YZ mirror. YZ and XY mirror are perpendicular to each other. So the angle of incidence for the YZ mirror will be (90° – 65°) = 25°. From this we can say that the angle of reflection for the mirror YZ is 25°.

103)

X = Persistence of vision

Y = (1/16) second

Z = Pictures.

The eye of a person exhibits a phenomenon called persistence of vision (X) due to which it can see the image of an object for a short duration of (1/16)th of a second (Y) even after the image has disappeared from his view. It is due to the persistence of vision we are able to see moving pictures (Z) on a television screen.

104)

Defect in eye of man A = Hypermetropia

Defect in eye of man B = Myopia

C = Convex lenses

D = Concave lenses

Man A has a defect of vision called Hypermetropia (A) due to which he cannot see the nearby the nearby objects clearly (though he can see the distant objects clearly). On the other hand, man B has a defect of vision called Myopia (B) due to which he cannot see the distant object clearly (though he can see the nearby objects clearly). The defect in man A can be corrected by using spectacles containing convex lenses (C) whereas the defect in man B can be corrected by using spectacles containing concave lenses (D).

105)

P = Kaleidoscope

Q = Periscope

A Student makes a device called kaleidoscope (P) by using three long and narrow strips of plane mirror inclined at 60° to one another which enables him to see beautiful patterns made by pieces of colored glass bangles. On the other hand, another student makes a device called Periscope (Q) by using two plane mirrors arranged parallel to each other which helps him to see a football match clearly even when some very tall persons are sitting in front of him on the ground.

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