Class-8 Subject Science Chapter-16 LIGHTS

 EVENTS CONVENT HIGH SCHOOL

12/10/2021      CLASS-8     SESSION 2021-22
SUBJECT : SCIENCE

chapter - 16
lIGHTS 

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Textbook Questions

Question 1.Suppose you are in a dark room. Can you see objects in the room? Can you see objects out¬side the room? Explain.
Answer:
When we are in a dark room then we cannot see objects in the room. We can see the objects outside the room, because out of the room the light is available and the rays of light can enter our eyes after reflection from the objects.

Question 2.Differentiate between regular and diffused reflection. Does diffused reflection mean the failure of the laws of reflection?
Answer:

Regular Reflection	Diffused Reflection
(i) All the reflected rays are parallel.	(i) The reflected rays are not parallel.
(ii) It occurs on a smooth and polished surface.	(ii) It occurs on the rough surface.
(iii) Reflected rays are in one direction.	(iii) Reflected rays are scattered in different directions.

No, diffuse reflection doesn’t mean the failure of laws of reflection.

Question 3.
Mention against each of the following whether regular or diffused reflection will take place when a beam of light strikes. Justify your answer in each case.

1. Polished wooden table
2. Chalk powder
3. Cardboard surface
4. Marble floor with water spread over it
5. Mirror
6. Piece of paper

Answer:

1. Regular reflection will take place because the surface is plane and polished.
2. Diffused reflection will take place because the surface is rough.
3. Diffused reflection will take place because the surface is rough.
4. Regular reflection will take place because the surface is smooth and plane.
5. Regular reflection will take place because the surface is plane and polished.
6. Diffused reflection will take place because the surface is rough.

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

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

Question 5 Fill in the blanks in the following.
(a) A person 1 m in front of a plane mirror seems to be ______ m away from his image.
(b) If you touch your ______ ear with a right hand in front of a plane mirror it will be seen in the mirror that your right ear is touched with _____
(c) The size of the pupil becomes _______ when you see in dim light.
(d) Night birds have _______ cones than rods in their eyes.
Answer:
(a) 2
(b) left, left hand
(c) larger
(d) lesser

Question.6 Choose the correct option in Questions 
1.The angle of incidence is equal to the angle of reflection
(a) Always
(b) Sometimes
(c) Under special conditions
(d) Never
Answer:
(a) Always

2. Image formed by a plane mirror is:
(a) virtual, behind the mirror and enlarged.
(b) virtual, behind the mirror and of the same size as the object.
(c) real at the surface of the mirror and enlarged.
(d) real, behind the mirror and of the same size as the object.
Answer:
(b) virtual, behind the mirror and of the same size as the object.

CLASS-7 SUBJECT-SCIENCE CHAPTER-15 LIGHTS.

 EVENTS CONVENT HIGH SCHOOL

12/10/2021      CLASS-7     SESSION 2021-22
SUBJECT : SCIENCE

chapter - 15
lIGHTS 

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Q.1.Fill in the blanks:
(a) An image that cannot be obtained on a screen is called ___________ .
(b) Image formed by a convex is __________ always virtual and smaller in size.
(c) An image formed by a __________ mirror is always of the same size as that of the object.
(d) An image which can be obtained on a screen is called a __________ image.
(e) An image formed by a concave __________ cannot be obtained on a screen.
Ans.(a) virtual image (b) mirror (c) plane (d) real (e) lens

Q.2.Mark ‘T’ if the statement is true and ‘F’ if it is false:
(a) We can obtain an enlarged and erect image by a convex mirror. (T/F)
(b) A concave lens always form a virtual image. (T/F)
(c) We can obtain a real, enlarged and inverted image by a concave mirror. (T/F)
(d) A real image cannot be obtained on a screen. (T/F)
(e) A concave mirror always form a real image. (T/F)
Ans. a) F (b) T (c) T (d) F (e) F

Q.3. Match the items given in Column I with one or more items of Column II

Ans.

Q.4.State the characteristics of the image formed by a plane mirror.
Ans.(i) Plane mirror forms an erect image.
(ii) It forms a virtual image.
(iii) Size of the image is same as that of the object.
(iv)Image is formed at the same distance behind the mirror as the object stands in front of it.
(v) Image formed is a laterally inverted image i.e., right hand side of the object seems to be the left hand side and vice-versa.

Q.5.Find out the letters of English alphabet or any other language known to you in which the image formed in a plane mirror appears exactly like the letter itself. Discuss your findings.
Ans.Letters like A, H, I, M, O, T, U ,V, W etc. appear same when seen through a plane mirror

Q.6.What is a virtual image? Give one situation where a virtual image is formed.
Ans.The image which cannot be taken on a screen is called virtual image. When some object is placed very close to the concave mirror we don’t get any image on the white screen placed behind the mirror. Such image is called virtual image.

Q.7. State two differences between a convex and a concave lens.

Q.8. Give one use each of a concave and a convex mirror.
Ans. Use of concave mirror:
Concave mirror is used by dentists to examine the teeth.
Use of convex mirror:
Convex mirror is used as side view mirror in vehicles

Q.9. Which type of mirror can form a real image?
Ans. Concave mirror can form a real image.