Class 7 Science Chapter 13 HOTS Questions - Light

Q1: How will you identify the three mirrors, i.e., convex, concave and plane mirror without touching them?
Ans: We can identify the mirrors by seeing the image formed by them.

• Images formed by plane mirror is always virtual, erect and of same size as that of object.
• Images formed by convex mirror is erect, virtual and smaller in size than the object.
• Image formed by concave mirror is real, inverted, virtual, erect, magnified and diminished depending upon the distance of object with respect to the mirror.

Q2: How can you obtain a real image of a distant object?
Ans: By using concave mirror or convex lens and a screen we can obtain a real image of a distant object.

Q3: The concave reflecting surface of a torch got rusted. What effect would this have on the beam of light from the torch?
Ans: The beam of light will be of lower intensity due to diffused or irregular reflection.

Q4: If the side mirror of a scooter is replaced by a plane mirror, will it cause any inconvenience to the driver?
Ans: Yes, it will cause inconvenience to the driver and he will not be able to see the traffic behind him properly.

Q5: Rajesh for observing dispersion of light, used light from laser torch to fall on a prism. Will he be able to observe a band of seven colours?
Ans: No, because laser torch gives out light of only one colour.

Q6: Mention the name of lens whioh can converge the sun’s rays to a point and burn a hole in the piece of paper.
Ans: Convex lens is a lens which can converge the sun’s rays to a point and burn a hole in the piece of paper.

Q7: 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: In case of convex lens, when we move the object far away from the lens, the size of image decreases and ultimately, when object is at infinity, it will form a point image at focus.

Q8: Two different types of lenses are placed on a sheet of newspaper. How will you identify them without touching?
Ans: On identifying the letters of newspaper, we can differentiate the two types of lenses.
If image is large or magnified, then the lens is a convex lens and if the image is smaller or diminished in size for all the positions of object, then the lens is concave .

Q9: 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: As we know that the side mirror of a scooter must be of convex mirror so that we can view a wide range of traffic spread over a large area. But if plane mirror is used, we are not able to see large area of traffic which may be difficult for driving vehicle and can cause accident.

Q10: A shopkeeper wanted to fix a mirror which will give a maximum view of his shop. What type of mirror should he use? Give reason.
Ans:

• If a shopkeeper wanted to fix a mirror which will give him maximum view of his shop, he should use convex mirror.
• In case of convex mirror, it will give a wider field of view, i.e. it can collect light from a large area spread over them.

Q11: 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:

• No, he will not observe band of seven colours because laser light consists of monochromatic light of single colour.
• But seven colours of bands are only observed, when a white light is passed through a prism and dispersion takes place.

Q12: Briefly explain why in ambulance words are written laterally inverted.
Ans: In case of mirror, the image formed by it is laterally inverted, i.e. left seems to be right and right seems to be left. So, in ambulance there is emergency for patients to reach hospital and by viewing in rear mirror, it can be easily identified of a vehicle and everyone give him a way.

Q13: Assume, a person is standing in front of a plane mirror. The distance between the mirror and his image is 6 m. If the person moves 2 m towards the plane mirror, what would be the distance between the person and his image?
Ans:
Since, the image is 6m away from the plane mirror. So, it means that the object is also 6m away from the mirror.

[Because OP = PI]
So, when the person moves 2 m towards the plane mirror, then the distance between the person and the plane mirror will be equal to (6 m – 2 m) = 4 m, this means that distance between the image and the mirror will be 4m.

The distance between the person and his image = PO’+ PI’= 4 + 4 = 8m

Q14: 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:

• On decreasing the distance between the object and lens, the size of the image increases, the nature of the lens will be convex type.
• If the distance between object and lens is less than the focus of the lens, then it forms a virtual image and this image cannot be obtained on a screen but formed on the same side of the object.

Q15: You are given three mirrors of different types.
How will you identify each one of them?
Ans: We can identify the mirrors by forming image of an object.

• Plane mirror In case of plane mirror, image will be virtual, erect and of same size as that of object.
• Concave mirror In case of concave mirror, image may be real, virtual and magnified or diminished.
• Convex mirror In case of convex mirror, image formed will always be virtual, erect and diminished.

Q16: 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 respectively are
(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: (c) plane mirror and convex mirror

Q17: 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: (b)
The distance between object and mirror is given by 0.5 + 0.5= 1 m.

Q18: 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 sunrise
Ans: (b) when the sun is behind you

Q19: 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: (c) both concave mirror and convex lens

Q20: An image formed by a lens is erect. Such an image could be formed by
(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: (b) concave lens provided the image is smaller than object