NCERT Solutions for Class 7 Science Chapter 15 Light

1. Fill in the blanks:

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

Answer: virtual image

(b) Image formed by a convex __________ is always virtual and smaller in size.

Answer: mirror

(c) An image formed by a __________ mirror is always of the same size as that of the object.

Answer: plane

(d) An image which can be obtained on a screen is called a _________ image.

Answer: real

(e) An image formed by a concave ___________ cannot be obtained on a screen.

Answer: lens

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)

Answer: False. [ Convex mirror form virtual diminished and erect. ]

(b) A concave lens always form a virtual image. (T/F)

Answer: True

(c) We can obtain a real, enlarged and inverted image by a concave mirror. (T/F)

Answer: True

(d) A real image cannot be obtained on a screen. (T/F)

Answer: False. [ Real images can be obtained on the screen, virtual image cannot be obtained on the screen. ]

(e) A concave mirror always form a real image. (T/F)

Answer: False. [ Concave mirror can form real and virtual images. Formation of real and virtual image depends on distance of object from mirror. ]

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:

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	(ii) Can form image of objects spread over a large area. (vi) The image is erect and smaller in size than the object.
(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	(v) The image is erect and of the same size as the object.

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

Answer: Some characteristics of the image formed by plane mirror are –

• Plane mirror forms erect image
• Image formed is laterally inverted
• Right side of object appears left side of the image
• Image formed is at same distance as that of object

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: Letters that are vertically symmetric appears exactly like the original letter in their image. By term vertically symmetric suggest that, if we divide a letter in 2 halves, then it first half will be same as its second half. In english alphabet such letters are A, H, I, M, O, T, U, V, W, X, Y.

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

Answer: Image of an object that cannot be captured on screen is called virtual image. Image formed by plane mirror is a virtual image.

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

Answer:

Convex Lens	Concave Lens
Thick in middle and thin at the edges	Thick at the edges and thin at the middle
Converges light rays falling on it	Diverges light rays falling on it
Able to form real image	Cannot form real image
Used in camera, telescopes, etc	Used in flashlights and correction of eye defects

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

Answer: Following are the uses of concave and convex mirror

• Concave mirrors:
  1. Dentist use concave mirrors to see enlarged images of patient’s teeth
  2. Used in reflecting telescope
• Convex mirrors:
  1. Used in mirror of vehicles to see traffic comming from behind
  2. Used on road turning to see who is comming from other side

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

Answer: Concave mirror

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

Answer: Concave lens

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

Answer: (ii) concave mirror – It forms virtual and larger image than object.

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: (iii) 6 m

Explanation: Plane mirror forms image at same distance as that of object.

Therefore, distance of object from mirror(d1) is equal to distance of image from mirror(d2).

It can be presented as d1 = d2 …. (1)

Now, distance between image and mirror is 4 m, d2 = 4m, therefore, d1= 4 m from (1)

If david moves 1 m towards mirror, therefore d1= d1-1 = 4-1= 3 = d2

Thus, distance between David and his image will be d1+d2 = 3+3 = 6 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: (iii) 4 m/s

Explanation: Object and image formed from plane mirror are always at same distance. Car is reversing with 2m/s speed and thus image will also be moving with speed of 2 m/s second. Therefore, speed at which image of truck appears to driver will be 2 m/s + 2m/s = 4m/s

Check other lessons NCERT Solutions for Class 7

Download free NCERT textbook class 7 Science – Chapter 15 Light