NCERT Exemplar for Class 7 Science Solutions Chapter 15 Light

Multiple Choice Questions

1. Boojho and Paheli were given one mirror each by their teacher. Boojho found his image to be erect and of the same size whereas Paheli found her image erect and smaller in size. This means that the mirrors of Boojho and Paheli are, respectively

a) Plane mirror and concave mirror.

b) Concave mirror and convex mirror.

c) Plane mirror and convex mirror.

d) Convex mirror and plane mirror.

Ans: The correct answer is option (c), Plane mirror and convex mirror. Plane mirror always forms an image of equal size, an erected image and convex mirror always forms an image erect and smaller in size.

2. Which of the following can be used to form a real image?

a) Concave mirror only.

b) Plane mirror only.

c) Convex mirror only.

d) Both concave and convex mirrors.

Ans: The correct answer is option (b), plane mirror. Plane mirror always forms an erect image of equal size.

3. If an object is placed at a distance of 0.5 m in front of a plane mirror, the distance between the object and the image formed by the mirror will be

a) 2 m

b) 1 m

c) 0.5 m

d) 0.25 m

Ans: The correct answer is option (b), 1 m.

The image formed or created by a plane mirror is at equal distance behind the plane mirror as the object is in front of it. So, now

The distance of object from plane mirror = 0.5 m

Then the distance of image from plane mirror = 0.5 m

Total distance between object and plane mirror = 0.5+0.5=1m

4. You are provided with a concave mirror, a convex mirror, a Concave lens and a convex lens. To obtain an enlarged image of an object you can use either

a) Concave mirror or convex mirror.

b) Concave mirror or convex lens.

c) Concave mirror or concave lens.

d) Concave lens or convex lens.

Ans: The correct answer is option (b), Concave mirror or convex lens. Enlarged images are formed by only a concave mirror or convex lens.

5. A rainbow can be seen in the sky

a) When the sun is in front of you.

b) When the sun is behind you.

c) When the sun is overhead.

d) Only at the time of sun rise.

Ans: The correct answer is option (b), when the sun is behind you. When the sun is behind you and the light is low, you can easily see rainbows during the rainy season.

6. An erect and enlarged image can be formed by

a) Only a convex mirror.

b) Only a concave mirror.

c) Only a plane mirror.

d) Both convex and concave mirrors.

Ans: The correct answer is option (b), only a concave mirror. Concave mirror forms a virtual, erect and enlarged image.

7. You are provided with a convex mirror, a concave mirror, a convex lens and a concave lens. You can get an inverted image from

a) Both concave lens and convex lens.

b) Both concave mirror and convex mirror.

c) Both concave mirror and convex lens.

d) Both convex mirror and concave lens.

Ans: The correct answer is option (c), both concave mirror and convex lens. Both concave mirror and convex lens can form inverted and real images of an object.

8. An image formed by a lens is erect. Such an image could be formed by a

a) Convex lens provided the image is smaller than object.

b) Concave lens provided the image is smaller than object.

c) Concave lens provided the image is larger than object.

d) Concave lens provided the image is of the same size.

Ans: The correct answer is option (b), Concave lens provided the image is smaller than object. The image of an object created by a concave lens is erect, virtual, and diminished.

Very Short Answer Questions

9. The image formed by a lens is always virtual, erect and smaller in size for an object kept at different positions in front of it. Identify the nature of the lens.

Ans: The lens is a “Concave lens”.

10. Fill in the blanks:

a) The inner surface of a steel spoon acts as a ___________ mirror.

Ans: Concave

b) The outer surface of a flat steel plate acts as a ___________ mirror.

Ans: Plane

c) The outer shining surface of a round bottom steel bowl acts as a __________ mirror.

Ans:  Convex

d) The inner surface of the reflector of a torch acts as a __________ mirror.

Ans: Concave

11. State whether the following statements are true or false.

(a) A concave lens can be used to produce an enlarged and erect image.

Ans: The given statement is false. A concave lens can only form an erect, diminished and virtual image of an object.

(b) A convex lens always produces a real image.

Ans: The given statement is false. A convex lens can form an inverted, diminished and real image of an object.

(c) The sides of an object and its image formed by a concave mirror are always interchanged.

Ans: The given statement is true.

(d) An object can be seen only if it emits light.

Ans: The given statement is false. Only if an object reflects light falling on it can it be seen.

Short Answer Questions

12. What type of mirror is used as a side mirror in a scooter? Why is this type of mirror chosen?

Ans: Convex mirrors are used as side mirrors on scooters. The convex mirror forms a diminished image of an object which is helpful for the driver to cover a wide area of view.

13. Observe the figures given as Figure 15.1 carefully

The given figures show the path of light through lenses of two different types, represented by rectangular boxes A and B. What is the nature of lenses A and B?

Ans: Lens A = Light rays are converging in the direction of point. So, this is a convex lens.

Lens B = Light rays are diverging from the direction of point. So, this is a concave lens.

14. Boojho made light from a laser torch to fall on a prism. Will he be able to observe a band of seven colours? Explain with a reason.

Ans: The laser light is made up of a particular colour. Thus, he will not be able to observe the band of all seven colours. They will only be observed, when white colour passes through the prism and dispersion takes place.

15. State the correct sequence (1-7) of colours in the spectrum formed by the prisms A and B, shown in Figure 15.2.

Ans: In figure A and figure B

16. The side mirror of a scooter got broken. The mechanic replaced it with a plane mirror. Mention any inconvenience that the driver of the scooter will face while using it?

Ans: A convex mirror is used as a side mirror on a scooter.

Inconveniences are

i) Less area visible on a plane mirror as compared to a convex mirror.

ii) Traffic behind the vehicle is hidden.

17. The concave reflecting surface of a torch got rusted. What effect would this have on the beam of light from the torch?

Ans: The torch will produce a dim and diffused beam with a lower intensity. Due to this, the object will not be clearly visible.

18. An erect and enlarged image of an object is formed on a screen. Explain how this could be possible.

Ans: If the object is placed upside down between F (focus) and 2F (centre of curvature) of the convex lens. An erect and enlarged image of an object is created as a result.

19. Two different types of lenses are placed on a sheet of newspaper. How will you identify them without touching?

Ans: If the letters of newspaper appear magnified, the placed lens is convex lens. If the letters of newspaper appear shortened, the placed lens is concave lens.

20. A shopkeeper wanted to fix a mirror which will give a maximum view of his shop. What type of mirror should he use? Give a reason.

Ans: A shopkeeper will fix a convex mirror. The convex mirror may create images of an object that are spread out across a broad area.

21. The distance between an object and a convex lens is changing. It is noticed that the size of the image formed on a screen is decreasing. Is the object moving in a direction towards the lens or away from it?

Ans: According to the question, the object is moving away from the lens.

In convex, the size of the image formed on screen will increase if an object is moved in the direction of that lens.

Long Answer Questions

22. Suppose we wish to obtain the real image of a distant tree. Explain two possible ways in which we can do it.

Ans: Two possible ways are

1. With the help of a “concave mirror” and screen, we can obtain the real image of a distant tree. “A concave mirror forms a real image of an object at its focus”. So, the real image of a distant tree will be formed.

2. With the help of a “convex lens” and screen, we can obtain the real image of a distant tree. “A convex lens forms a real image of an object at its focus”. So, the real image of a distant tree will be formed.

23. It was observed that when the distance between an object and a lens decreases, the size of the image increases. What is the nature of this lens? If you keep on decreasing the distance between the object and the lens, will you still able to obtain the image on the screen? Explain.

Ans: Nature of the asked lens is “Convex Lens”. When we place an object close to a convex lens, then the formed image will be Virtual. This image cannot be obtained on screen.

24. You are given three mirrors of different types. How will you identify each one of them?

Ans: By forming images of an object, you can identify all three mirrors:

i) Plane Mirror: The formed image of an object by the mirror is erect, virtual and of the same size (of that object).

ii) Concave Mirror: The formed image of an object by the mirror is inverted, virtual and diminished (according to the position of an object).

iii) Convex Mirror: The formed image of an object by the mirror is erect, virtual and diminished (according to the position of an object). 

About Light - Class 7 Science Chapter 15

Light is simply energy travelling from one place to another, and it does not require any medium to travel and can travel in space, Unlike sound.

Light is a fascinating topic for young minds, which lets them think about their limits. This chapter, named Light, provides a proper explanation of various concepts on the light.