CBSE Class 8 Science Light Assignment

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

Question 10- Draw a labelled sketch of the human eye.

Answer-

 

Question 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 advise?

Answer- Because of the intensity of the laser light is very high, and it is harmful to the human eyes. It can cause damage to the retina and leads to blindness.

 

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

Answer- (i) Visit an eye specialist regularly.

(ii) Avoid reading in dim light and very bright light.

(iii) Avoid direct exposure of sunlight to the eye.

(iv) Clean your eyes with cold water quickly if dust particles or small insects enter your eye.

(v) Do not rub your eyes.

(vi) Maintain a distance of at least 25 cm between the book and your eyes while reading.

 

Question 13- What is the angle of incidence of a ray if the reflected ray is at an angle of 90° to the incident ray?

Answer- 45º.

 

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

Answer- Infinite number of images.

 

Question 15- Two mirrors meet at right angles. A ray of light is incident on one at an angle of 30° as shown in Fig. 16.19. Draw the reflected ray from the second mirror.

1. Draw a diagram to show the reflection of light from a plane mirror. Label the following on the diagram:

(a) Plane mirror (b) Incident ray (c) Reflected ray

(d) Point of incidence (e) Normal (f) Angle of incidence

(e) Angle of reflection.

2. How many reflected rays can there be for a given single incident ray falling on a plane mirror?

3. State the Laws of Reflection of Light.

4. An incident ray makes an angle of 750 with the surface of a plane mirror. What will be the angle of reflection?

5 A ray of light is incident normally {perpendicularly} on a plane mirror. Where will this ray of light go after reflection from the mirror ?

6 What is the difference between regular reflection and diffuse reflection of light ?

7 State whether the following statement is true or false :

Diffuse reflection means the failure of the laws of reflection of light.

8 Draw a labeled diagram showing how a plane mirror forms an image of a point object placed in front of it.

9 If an object is placed at a distance of 7.5 cm from a plane mirror, how far would it be from its image ?

10 You see your image in a plane mirror? State two characteristics of the image so formed.

11 Name the phenomenon responsible for the following effect:

When we sit in front of a plane mirror and write with our right hand, it appears in the mirror that we are writing with the left hand.

 12 Fill in the following blanks:

• If you touch your------ ear with right hand in front of a plane mirror, it will be seen in the mirror that your right ear is touched with -------

13 How are the two plane mirrors in a periscope arranged?

• With respect to one another?

• With respect to sides of the tube?

14 Explain how, a hair dresser makes you see hair at the back of your head after the hair cut is complete.

15 How many images of an object will be formed when the object is placed between two plane mirrors which are inclined at the following angles to one another?

(a) 120° (b) 45° (c)180° (d) 60° (e) 90°

16 What will be the number of images formed when an object is placed between two parallel plane mirrors facing each other?

17 Describe the construction of a kaleidoscope.

18 How many plane mirror strips are there in a kaleidoscope? How are they arranged?

19 State one use of kaleidoscope.

20 What is meant by “dispersion of light “? Name a natural phenomenon which is caused by the dispersion of sunlight in the sky.

21. What are the functions of the following parts of the eye?

(a) Iris (b) Ciliary muscles (c) Retina (d) optic nerve.

22 Name the cells on the retina of an eye:

(a) which are sensitive to bright light.

(b) which are sensitive to dim light.

(c) which produces sensation of colours.

23. Explain why, we cannot see our surroundings clearly when we enter a darkened cinema hall from bright sunshine but our vision improves after sometime.

24. What happens to the size of the pupil of our eye:

(a) in dim light?

(b) in bright light?

25. What is the range of vision of a normal human eye?

26. Name the phenomenon which enables us to see movies in cinema hall.

27. What is meant by ‘persistence of vision’?

28 What are the various defects of eye? Explain them in brief? Also suggest the corrective measures of the defects.

Q.1. Complete the following sentences

a) The coloured, disc shaped diaphragm in the eye is called the …………..

b) In regular reflection, the reflected rays remain ……………. to each other.

c) The number of image is infinite when the angle between the mirrors is …………….

Q.2.Name the following

a) Light of all colours are mixed in a certain proportion.

b) Blindness arising out of lack of Vitamin A in the diet.

c) The rays of beam are reflected in different directions.

d) A protective white membrane covering most of the eye ball.

Q.3.Define the following terms

a) Braille

b) Lateral Inversion

c) Kaleidoscope

d) Dispersion

e) Spectrum

f) Accommodation

g) Cataract

Q.4.Differentiate between the following

b) Reflection and Refraction

c) Myopia and hypermetropia

Q.5.Give reasons for the following

a) A shiny metal utensil forms an image, but the image is not clear as that formed by a mirror.

b) You see a clear, bright image of an object in a mirror.

c) When a mirror is held behind your head after a haircut, not only you see the back of your head, you also see innumerable images of yourself.

Q.6.Answer the following in not more than 20 words.

b. What happens to the rays of light in case of diffuse reflection?

c. An object is placed 20 cm in front of a plane mirror. Where is the image formed? How far is it from the mirror?

d. An object is placed between two mirrors that are at 60° to each other. How many images are formed?

Q.7.Answer the following in not more than 40 words.

a. State the laws of reflection of light.

b. What do you understand by the blind spot of the eye?

Q.8.Answer the following in not more than 100 words.

a. What vision related problems occur when the diet lacks Vitamin A?

b. Describe the structure of the eye with the help of a diagram.

1.Light is a form of ___________ radiation.
(A) Electromagnetic.
(B) Mechanical.
(C) Longitudinal.
(D) None of these.

2.The wavelength of visible light is in the range:
(A) 4 × 10^-7 m to 8 × 10^-7 m.
(B) 4 × 10⁷ m to 8 × 10⁷ m.
(C) 4 × 10³ m to 8 × 10³ m.
(D) None of these.

3.An ________ image can be obtained on a screen.
(A) Real.
(B) Virtual.
(C) Upright.
(D) Inverted.

4.According to the laws of reflection:
(A) Angle i = Angle r
(B) Sine i = sine r
(C) Sine i / Sine r = constant
(D) All of these.

5.The colour of an object is determined by
(A) The colour of light reflected by it:
(B) The colour of light absorbed by it.
(C) The colour of light incident on it only.
(D) None of the above.

6.Human eye is one of the most valuable and sensitive organ that:
(A) Enables us to see the wonderful world and colours around us.
(B) Can identify the objects.
(C) Is like a camera.
(D) All of these.

7.The ray of light strikes at the surface of mirror is called:
(A) Reflected ray.
(B) Incident ray.
(C) Normal ray.
(D) None of these.

8.Which of the following does not describe working of the human eye?
(A) Light enters the eye through a thin membrane called the cornea.
(B) Rainbow is formed due to splitting of white light.
(C) Iris is a dark muscular diaphragm that controls the size of the pupil for.
(D) Regulating the amount of light entering into the eye.

9.Electrical signals generated by light sensitive cells of retina are sent to the brain via:
(A) Motor nerves.
(B) Optic nerves.
(C) Sensory nerves.
(D) Spinal cord.

10.Least distance of vision for a normal eye is:
(A) 25 cm.
(B) 1 m.
(C) 30 cm.
(D) Infinity.

11.The eye lens forms an ___________ and _________ image of the object on the retina.
(A) Virtual and erect.
(B) Real and inverted.
(C) Real and erect.
(D) Virtual and erect.

12.Iris contracts the pupil:
(A) In bright light.
(B) To allow less light to enter.
(C) In darkness.
(D) Only (a) and (b).

13.Colour blindness is the name given to:
(A) Inability to distinguish between colours.
(B) Inability to see anything.
(C) Inability to see in dark.
(D) Inability to see in bright light.

14.The transparent front part of eye is called:
(A) Iris.
(B) Cornea.
(C) Pupil.
(D) Cone.

15.Reflection from a rough surface is called:
(A) Regular reflection.
(B) Diffused reflection.
(C) Irregular reflection.
(D) Only (b) & (c).

16.Reflection from a smooth surface is called:
(A) Regular reflection.
(B) Diffused reflection.
(C) Irregular reflection.
(D) None of these.

17.If angle of incidence is 30° than angle of reflection will be
(A) 60°
(B) 0°
(C) 30°
(D) None.

18.If the angle between incident and reflected ray is 50° than find the angle of incidence.
(A) 50°
(B) 30°
(C) 25°
(D) 100°

19.Splitting of white light on passage through a triangular prism:
(A) Takes place due to the inclined surfaces.
(B) Is known as dispersion of light.
(C) Is into a band of seven colours known as spectrum.
(D) All of these.

20.What is the angle of incidence of a ray if the reflected ray is at an angle of 90° to the incident ray?
(A) 500
(B) 600
(C) 450
(D) 900

21.The image formed by plane mirror is:
(A) Erect.
(B) Upside.
(C) Real.
(D) All of these.

22.The size of image formed by the plane mirror is………….the size of object.
(A) smaller than
(B) bigger than
(C) equal to
(D) None.

23.Splitting of white light into seven colours is known as:
(A) Dispersion.
(B) Reflection.
(C) Refraction.
(D) None of these.

24.Cataract is a condition:
(A) When the crystalline lens becomes milky and cloudy.
(B) That may cause partial or complete loss of vision.
(C) That can be rectified through a cataract surgery.
(D) All of these.

25.The angle between incident ray and normal is known as:
(A) angle of reflection.
(B) angle of incidence.
(C) angle of refraction.
(D) None of these.

26.The angle between reflected ray and normal is known as:
(A) angle of reflection.
(B) angle of incidence.
(C) angle of refraction.
(D) None of these.

27.The line at right angle to the mirror surface at the point of incidence is called:
(A) Incidence ray.
(B) Reflected ray.
(C) Normal.
(D) None.

28.If an object is placed at a distance of 8 cm in front of a plane mirror, how far its image will form from the mirror?
(A) 16 cm.
(B) 8 cm.
(C) 4 cm.
(D) 10 cm.

29.If an object is placed at a distance of 10 cm in front of a plane mirror, how far would it be from its image?
(A) 16 cm.
(B) 20 cm.
(C) 14 cm.
(D) 10 cm.

30.If the distance between the object and its image in a plane mirror is 14.6 cm, how far is the object from the mirror?
(A) 14.6 cm.
(B) 7.3 cm.
(C) 29.2 cm.
(D) None of these.

31.The image formed in a plane mirror is sideways reversed. This phenomenon is called:
(A) Lateral inversion.
(B) Dispersion.
(C) Splitting.
(D) Refraction.

32.An object 5 cm high is placed in front of a plane mirror. What is the size of the image formed?
(A) 2.5 cm.
(B) 10 cm.
(C) 5 cm.
(D) None of these.

33.Which types of cells present on retina respond to the intensity of light?
(A) Cones.
(B) Rods.
(C) Both.
(D) None.

34.Which types of cells present on retina respond to the colours?
(A) Cones.
(B) Rods.
(C) Both.
(D) None.

35.A chicken's eye has very few ……….. shaped cells.
(A) Cone.
(B) Rod.
(C) Both.
(D) None.

36.The human eye forms the image of an object at its:
(A) Cornea.
(B) Iris.
(C) Pupil.
(D) Retina.

37.The part of eye, which is equivalent to the photographic film in a camera is:
(A) Cornea.
(B) Iris.
(C) Pupil.
(D) Retina.

38.The part, which controls the amount of light entering the eye, is
(A) Cornea.
(B) Iris.
(C) Pupil.
(D) Retina.

39.What kind of retinal cells are lacking in a person suffering from colour blindness?
(A) Cone.
(B) Rod.
(C) Both.
(D) None.

40.The image, which can be obtained on a screen is called:
(A) Real.
(B) Virtual.
(C) Upside.
(D) None.

41.Name the form of energy which enables us to see the objects?

42.What types of waves are light waves?

43.Define a ray of light.

44.Define a beam of light?

45.Give an example of best reflector of light.

46.What type of image is formed in a plane mirror?

47.What type of image is formed on a cinema screen?

48.If an object is placed at a distance of 10 cm in front of a plane mirror, how far would it be forms its image?

49.Give any three phenomena shown by light.

50.How can visually challenged persons read and write?

51.What do you mean by reflection of light?

52.How do we see objects?

53.If the incident ray strikes the mirror at 900, what will be the angle of reflection?

54.If angle of incident is 300 then what will be the value of angle of reflection?<

55.Name the instrument based on multiple reflection used to create new designs

56.Name one means of communication provided by light.

57.State the laws of reflection.

58.Write the names of important parts of eye.

59.A celestial body that revolves around a planet is known as

60.Shooting stars are actually not .

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61.Name two types of sources of light.

62.Define dispersion of light.

63.What is blind point?

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64.Why the world AMBULANCE is written as its mirror image in front of the hospital vans?

65.What do you mean by lateral inversion?

66.Draw a neat and labeled diagram of human eye.

67.Why is it important to take care of our eyes? Mention some activities that may cause damage to our eyes.

68.Write the functions of the following:
(a) Optic nerves.
(b) Retina.
(c) Cornea.

69.What do you mean by multiple reflection?

70.What is the angle of incidence of a ray if the reflected ray is it an angle of 90° to the incident ray

71.How many images of a candle will be formed if it is placed between two a parallel plane mirrors separated by 40 cm

72.How many images of a candle will be formed if it is placed between two a parallel plane mirrors separated by 40 cm

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73.Define regular and irregular reflection with the help of diagrams.

74.What are the two laws of reflection? Calculate angle of incidence and angle of reflection from the given diagram.

75.What are the characteristics of the image formed by a plane mirror? How is the position of image related to the position of the object?