NCERT CLASS 7 SCIENCE CHAPTER 15 LIGHT
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NCERT CLASS 7 SCIENCE CHAPTER 15 LIGHT
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NCERT CLASS 7 SCIENCE CHAPTER 15 LIGHT
Question Answers
NCERT IN – TEXT QUESTIONS OF BOOJHO AND PAHELI
Q.1 Paheli wants to know, what makes things visible to us? Boojho thinks that objects are visible only when light reflected from them reaches our eyes. Do you agree with him? (Page 176)
Ans. Yes , I agree with him.
Q.2 Boojho noted in his notebook: Is it not surprising that my image is of the same size as me whether the mirror is small or large? (Page 177)
Ans. Yes.
Q.3 Paheli made a note in her notebook: In a plane mirror the image is formed behind the mirror. It is erect, of the same size and is at the same distance from the mirror as the object is in front of it. (Page 177)
Ans. Yes.
Q.4 Boojho saw an ambulance on the road. He was surprised to see that the word ‘AMBULANCE’ in front was written in a strange manner. (Page 178)
Ans. When the driver vehicle ahead of an ambulance looks in her/his rear view mirror, he/she can read ‘AMBULANCE’ written on it and give way to it. It is the duty of every one of us to allow an ambulance to pass without blocking its way.
NCERT TEXTBOOK EXERCISE (Pages 189 – 190)
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 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 from a real image. (T/F)
Ans. (a) False (F); (b) True (T); (c) False (F); (d) False (F); (e) False (F).
Q.3 Match the items given in column I with one or more items of column II
| Column I | column II |
| (a) A plane mirror | (i) Used as a magnifying glass. |
| (b) A convex mirror | (ii) Can form image of object speed over a large area. |
| (c) A convex lens | (iii) Used by dentists to see enlarged image of teeth. |
| (d) A concave mirror | (iv) The image is always inverted and magnified. |
| (e) A concave lens | (v) The image is erect and of the same size as the object. |
(vi) The image is erect and smaller in size than the object. |
Ans. (a)(v); (b) (ii); (c) (i); (d) (iii); (e) (vi).
Q.4 State the characteristics of the image formed by a plane mirror.
Ans. The characteristics of the image formed by a plane mirror are:
(i) It forms and erect image.
(ii) It forms a virtual image.
(iii) It forms the image behind the mirror.
(iv) The size of the image is same as that of the object.
(v) It forms the image at the same distance behind the mirror as the object stands infront of it.
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, Vnand W.
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 a virtual image.
For example, when an object is placed very close to the concave mirror, we do not get any image of that object on the white screen placed behind the mirror. This type of image is known as virtual image.
Q.7 State two differences between a convex and a concave lens.
Convex lens
(i) These are thick at the middle and thin at the edge.
(ii) They can form magnified image.
Concave lens
(i) These are thin at the middle and thick at the edge.
(ii) The image formed by these lens are always diminished in size.
Q.8 Give one use each of a concave and a convex mirror.
Ans. Use of Concave Mirror: It is used by dentists to examine the teeth.
Use of Convex Mirror: It is used in vehicles as rear view mirror.
Q.9 Which type of mirror can form a real image?
Ans. Concave mirror.
Q.10 Which type of lens forms always a virtual image?
Ans. Concave lens.
Choose the correct option: (11-13)
Q.11 A virtual image larger than the object can be produced by a:
(i) concave lens (ii) concave mirror
(iii) convex mirror (iv) plane mirror.
Q.12 David is observing his image in a plane mirror. The distance between the mirror and his image is 4m. If he moves 1 m towards the mirror, then the distance between David and his image will be:
(i) 3m (ii) 5m (iii) 6m (iv) 8m.
Q.13 The rear view mirror of a car is a plane mirror. A driver is reversing his car at a speed of 2 m/s. The driver sees in his rear view mirror the image of a truck parked behind his car. The speed at which the image of the truck appears to approach the driver will be:
(i) 1 m/s (ii) 2 m/s (iii) 4 m/s (iv) 8 m/s.
Ans. 11. (ii) concave mirror; 12. (iii) 6m; 13.(iii) 4m/s.
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