NCERT solutions for class 7 science chapter -15
Light
Q.1.Fill in the blanks:
(a) An image that cannot be obtained on a screen is called virtual image.
(b) Image formed by a convex is mirror 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 can be obtained on a screen is called a real image .
(e) An image formed by concave lens cannot be obtained on a screen.
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. Ans. False
(b) A concave lens always form a virtual image.
Ans. True
(c) We can obtain a real, enlarged and inverted image by a concave mirror.
Ans. True
(d) A real image cannot be obtained on a screen.
Ans. False
(e) A concave mirror always form a real image.
Ans. False
Q.3. Match the items given in Column I with one or more
items of Column II
Ans.
| Column I | Column II |
| (a) A plane mirror
(b) A convex mirror
(c) A convex lens (d) A concave mirror
(e) A concave lens |
(v) The image is erect and of the same size
as the object. (ii) Can form image of object spread over a large area. (i) Used as a magnifying glass. (iii) Used by dentists to see enlarged image of teeth. (vi) The image is erect and smaller in size than the object.
|
Q4. 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
Q6. What is a virtual image? Give one situation where a virtual image is formed.
Ans. The mage 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.
Q7. State two differences between a convex and a concave lens.
Ans.
| Convex lens | Concave lens |
| (i) Convex lens can form both real and virtual image.
(ii) It can form magnified image
|
(i) Concave lens always form a virtual image.
(ii) Image is always diminished in size. |
Q8. Give one use each of a concave a convex mirror.
Ans. 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.
Q.10. Which type of lens forms always a virtual image?
Ans. Concave lens always forms a virtual image.
Choose the correct option in Questions 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
Ans. (ii) concave mirror
Q.12. David is observing his image in a plane mirror. Die 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
Ans. (iii) 6 m
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 mew 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. (ii) 4 m/s
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