Chapter 15 Light

By | March 16, 2019

Class 7 | Science | Chapter 15 | Light | NCERT Solutions

Question 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.

Answer 1 (a) An image that cannot be obtained on a screen is called 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.

Question 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)

Answer 2 (a) We can obtain an enlarged and erect image by a convex mirror: (F)
(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: (F)
(e) A concave mirror always form a real image: (F)

Question 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 objects spread 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.

Answer 3

Answer 3

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

Answer 4 Characteristics of the image formed by a plane mirror are:

1) It forms an erect and virtual image.

2) Size of the image is same as that of the object.

3) Image is formed at the same distance behind the mirror as the object stands in front of it.

4) 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.

Question 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 5 A, H, I, M, O, T, U ,V, W are the letters which form same image as the letter is.

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

Answer 6 The image which cannot be obtained on a screen is called virtual image. Plane mirror always form virtual image.

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

Answer 7

Convex Lens Concave Lens
It can form both real and virtual image. It always form a virtual image.
It can form magnified image. Image is always diminished in size.

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

Answer 8 Concave mirror is used by dentists to examine the teeth.

Convex mirror is used as side view mirror in vehicles

Question 9. Which type of mirror can form a real image?

Answer 9 Concave mirror can form a real image.

Question 10. Which type of lens forms always a virtual image?

Answer 10 Concave lens

Choose the correct option in questions 11–13

Question 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

Answer 11 (ii) concave mirror

Question 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 12 (iii) 6 m 

Question 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 13 (ii) 2 m/s

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