NCERT Solutions for Class 7 Science Chapter 15 Light
NCERT solutions for class 7 science chapter 15 light exercise:
- 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:
(a) virtual image. Only real images can be obtained on the screen.
(b) mirror.
(c) plane.
(d) real image. On these type of images can be obtained on the screen.
(e) concave lens. As virtual images cannot be obtained on the screen.
- 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:
(a) False. As the size of the image formed is smaller.
(b) True.
(c) True as the concave mirror gives a real and enlarged image.
(d) False. Real images can be obtained on screens whereas virtual images cannot be.
(e) False. As the nature of the image is decided by the distance between the object and mirror.
- 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 an image of objects spread over a large area. |
|
(c) A convex lens |
(iii) Used by dentists to see an 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:
(a) The image formed by a plane mirror is erect and of the same size.
(b) The image formed by a concave mirror is inverted and magnified. Also, they can form images of objects spread over a large area.
(c) A convex lens is used as magnifying glasses.
(d) A concave mirror is used to see enlarged images.
(e) The image formed by a concave lens is erect and smaller in size.
4 . State the characteristics of the image formed by a plane mirror.
Answer:
An image formed by a plane mirror is:-
(i) virtual
(ii) erect
(iii) of the same size
5 . Find out the letters of the 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 letter which has vertical symmetry will have this property.
In English alphabets, we have A, H, I, M, O, T, U, W, X, X, Y that appears exactly like itself in the plane mirror.
- What is a virtual image? Give one situation where a virtual image is formed.
Answer:
The image which can be screened (or obtained on screen) is known as a virtual image.
For e.g. in case of a candle which is placed in front of a plane mirror, we observe a virtual image of the candle formed behind the mirror.
7 . State two differences between a convex and a concave lens.
Answer:
The basic difference between the two are given below:-
(i) In the case of a convex lens, it converges the falling rays of light whereas in the case of the concave lens the rays diverge.
(ii) A concave lens has thick edges and is thin at the middle but the convex lens is thick at the middle.
- Give one use each of a concave and a convex mirror.
Answer:
The side-view mirror in a vehicle is a convex mirror for getting wider view of the rear.
To see an enlarged image of teeth, dentists use a concave mirror.
- Which type of mirror can form a real image?
Answer:
A concave mirror can form real images which can be obtained on the screen. The nature of the image formed by these mirrors depends upon the distance between the object and mirror.
10 . Which type of lens forms always a virtual image?
Answer:
The images formed by a concave lens is always virtual, magnified and erect in nature.
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 :
The correct answer is a concave mirror. The image formed by a concave mirror can be both virtual or real depending on the position of the object. Also, the image obtained is magnified.
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:
We are given the distance between the mirror and his image = 4 m
Now, if David moves 1 m towards the mirror, then the distance is = 4 − 1 = 3 m
Hence, the distance between David and his image is = 3 + 3 = 6 m.
13 . The rearview 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:
We are given that the speed of the car is 2 m/s which implies, the car is approaching the truck with a speed of 2 m/s.
Hence the speed at which the image of the truck appears to approach the driver will be: 2 2 = 4 m/s