Chapter 15 . Light | Science | CBSE Class VII (7th) | Lesson Exercises

Chapter 15 . Light | Science | CBSE Class VII (7th) | Lesson Exercises

Exercises : Solution
1. Fill in the blanks:
(a) An image that cannot be obtained on a screen is called a virtual image.
(b) Image formed by a convex  mirror  is always virtual and smaller in size.
(c) An image formed by a plane 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 real image.
(e) An image formed by a concave lens cannot be obtained on a screen.

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)
(b) A concave lens always form a virtual image. (T)
(c) We can obtain a real, enlarged and inverted image by a concave mirror. (T)
(d) A real image cannot be obtained on a screen. (T)
(e) A concave mirror always form a real image. (F)

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

Column I	Column II
(a) A plane mirror (b) A convex mirror (c) A convex lens (d) A concave mirror (e) A concave lens	(i) Used as a magnifying glass.  (ii) Can form image of objects (iii) Used by dentists to see enlarged image of teeth. (iv) The image is always inverted and magnified.                      (v) The image is erect and of the same size as the object. (vi) The image is erect and smaller

Solution :

Column I	Column II
(a) A plane mirror	(v) The image is erect and of the same size as the object.
(b) A convex mirror	(vi) The image is erect and smaller
(c) A convex lens	(i) Used as a magnifying glass.
(d) A concave mirror	(iii) Used by dentists to see enlarged image of teeth.
(e) A concave lens	(vi) The image is erect and smaller

4. State the characteristics of the image formed by a plane mirror.

 Answer : 

1. An image formed by a plane mirror is erect and of the same size as the object.
2. The image formed by the plane mirror is at the same distance behind the mirror as the object is in front
   of it.
3. The sides of an image formed by a plane mirror gets interchanged. In the mirror the ‘right’ appears ‘left’ and the ‘left’ appears ‘right’.
4. Only sides are interchanged; the image does not appear upside down.

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.

Answer : The image of following  English Alphabet, formed in a plane mirror  appears exactly like the letter itself : 

1. A
2. H
3. I
4. M
5. O
6. T
7. U
8. V
9. W
10. X

 6. What is a virtual image? Give one situation where a virtual image is formed.

Answer : Virtual Image : An image which cannot be obtained on a screen is called a virtual image.

A virtual image can be formed  by a plane mirror, convex mirror, concave mirror, convex lens and concave lens.  Polished Metallic surface or liquid surface such as lakes or water bodies can also form a virtual image

7. State two differences between a convex and a concave lens.
  Answer : Two difference between a convex and a concave lens are as given below :

Convex Lens	Concave Lens
Convex lenses are thicker in the middle than at the edges. A convex lens can forms real and inverted image. When the object is placed very close to the lens, the image formed is virtual, erect and magnified. A convex lens can be used as a magnifying glass A convex lens converges (bends inward) the light generally falling on it	Concave lenses are thinner in the middle than at the edges. A concave lens always forms erect, virtual and smaller image than the object. A concave  lens can not be used as a magnifying glass A concave lens diverges (bends outward) the light.

8. Give one use each of a concave and a convex mirror.
  Answer : 

1. Concave Mirror : It is used by dentists to see enlarged image of teeth.
2. Convex Mirror :It is used as view mirror in bus, cars or side mirrors in scooters.  Convex mirrors can
   form images of objects spread over a large area. So, these help the drivers to see the traffic behind them .

9. Which type of mirror can form a real image?
  Answer : A concave mirror can form a real and inverted image. When the object is placed very close to the mirror, the image formed is virtual, erect and magnified.

10. Which type of lens forms always a virtual image?
  Answer : A concave lens always forms a  virtual, erect,  and smaller image than the object.

Choose the correct option in questions 11–13
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
Correct Option : (ii) concave mirror
12. David is observing his image in a plane mirror. The distance between the mirror and his image is 4 m. If he moves 1 m towards the mirror, then the distance between David and his image will be
(i) 3 m (ii) 5 m
(iii) 6 m (iv) 8 m
Answer :(i) 3 m 
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
Answer :  (ii) 2 m/s

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Chapter 15 . Light  | Science | CBSE NCERT Class VII (7th) | Lesson  Exercises

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Did you know?

The mirrors can be used as weapons. Archimedes, a Greek scientist, is said to have done just that more than two thousand years ago. When the Romans attacked Syracuse, a coastal city-state in Greece, Archimedes used mirrors arranged as shown in Fig. 15.34. The mirrors could be moved in any direction. They were positioned such that they reflected the sunlight on the Roman soldiers. The soldiers were dazzled by the sunlight. They did not know what was happening. They got confused and ran away. This was an example of triumph of ideas over military might.