NCERT Solutions for Class 7 Science Chapter 15 Light are provided here with simple step-by-step explanations. These solutions for Light are extremely popular among Class 7 students for Science Light Solutions come handy for quickly completing your homework and preparing for exams. All questions and answers from the NCERT Book of Class 7 Science Chapter 15 are provided here for you for free. You will also love the ad-free experience on Meritnation’s NCERT Solutions. All NCERT Solutions for class Class 7 Science are prepared by experts and are 100% accurate.
Page No 80:
Question 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.
Answer:
Plane mirror forms erect and of same size image of an object. Convex mirror forms erect but smaller size image behind the mirror.
Hence, the correct answer is option (c).
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Question 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.
Answer:
Plane mirror and convex mirror forms virtual image only. Concave mirror forms both real and virtual image depending upon the position of an object with respect to the mirror.
Hence, the correct answer is option (a).
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Question 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
Answer:
Image formed by the plane mirror is virtual, erect and at same distance from mirror as that of object behind the mirror.
Distance between object and its image = 0.5 m + 0.5 m = 1 m
Hence, the correct answer is option (b).
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Question 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.
Answer:
To obtain an enlarged image of an object, we can use either concave mirror or convex lens. Convex mirror and concave lens forms diminished image of an object.
Hence, the correct answer is option (b).
Page No 80:
Question 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.
Answer:
A rainbow can be seen in the sky, when the sun is behind you.
Hence, the correct answer is option (b).
Page No 81:
Question 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.
Answer:
Concave mirror can form virtual, erect and enlarged image, of an object placed between pole and focus of the mirror.
Hence, the correct answer is option (b).
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Question 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.
Answer:
Both concave mirror and convex lens can form inverted and real image of an object.
Hence, the correct answer is option (c).
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Question 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.
Answer:
Image formed by concave lens is virtual, smaller and erect.
Hence, the correct answer is option (b).
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Question 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.
Answer:
The image formed by the concave lens is always virtual, erect and smaller in size for an object kept at different positions in front of it.
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Question 10:
Fill in the blanks:
(a) The inner surface of a steel spoon acts as a ___________ mirror.
(b) The outer surface of a flat steel plate acts as a ___________ mirror.
(c) The outer shining surface of a round bottom steel bowl acts as a __________ mirror.
(d) The inner surface of the reflector of a torch acts as a __________ mirror.
Answer:
(a) concave
(b) plane
(c) convex
(d) concave
Page No 82:
Question 11:
State whether the following statements are True or False.
(a) A concave lens can be used to produce an enlarged and erect image.
(b) A convex lens always produces a real image.
(c) The sides of an object and its image formed by a concave mirror are always interchanged.
(d) An object can be seen only if it emits light.
Answer:
(a) False ( as concave lens form diminished image)
(b) False ( convex lens forms both real and virtual image)
(c) True
(d) False (object can also be seen if it reflects light incident on it)
Page No 82:
Question 12:
What type of mirror is used as a side mirror in a scooter? Why is this type of mirror chosen?
Answer:
Convex mirror is used as a side mirror in a scooter. The convex mirror forms diminished image of an object, which is helpful for the driver to cover a wide area of view.
Page No 82:
Question 13:
Observe the figures given as given figure 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?
Answer:
The box A represents a converging lens which is also known as convex lens, while box B represents diverging or concave lens.
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Question 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.
Answer:
No, Boojho will not be able to observe the band of seven colors because laser light is made up of only a single color. White light is a mixture of seven colors light. So, if white light is made to fall on a prism, then it will split in seven colors in order of their wavelengths.
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Question 15:
State the correct sequence (1-7) of colours in the spectrum formed by the prisms A and B, shown in the given figure
Answer:
For prism A, the seven colors from top are:
1. Red,
2. Orange,
3. Yellow,
4. Green,
5. Blue,
6. Indigo,
7. Violet.
For prism B, the seven colors from top are:
1. Violet,
2. Indigo,
3. Blue,
4. Green,
5.Yellow,
6. Orange,
​7. Red.
Page No 83:
Question 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?
Answer:
Convex mirror forms image of an object spread over a large area and helps the driver to see traffic behind him, while the plane mirror forms image of an object spread over a smaller area. So, if the side mirror of scooter is replaced by a plane mirror, then the driver will not be able to see a large area (or traffic) behind him, due to which he/she may not drive properly.
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Question 17:
The concave reflecting surface of a torch got rusted. What effect would this have on the beam of light from the torch?
Answer:
If the concave reflecting surface of a torch gets rusted, it will not be able to reflect the light properly. So, light will be diffused with lower intensity, i.e., the intensity of the light coming out from the torch will be lower.
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Question 18:
An erect and enlarged image of an object is formed on a screen. Explain how this could be possible.
Answer:
Only real image can be obtained on the screen. So, if an object is placed upside down (inverted object) between the focus and center of curvature of concave mirror or a convex lens, then erect and enlarged image can be obtained on the screen.
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Question 19:
Two different type of lenses are placed on a sheet of newspaper. How will you identify them without touching?
Answer:
If the image of the letters of the news paper looks magnified, then the lens is a convex lens. Because the enlarged image is formed of an object placed between the focus and pole of a convex lens.
If the image of the letters of the news paper looks diminished, then the lens is a concave lens. Because the concave lens always forms a diminished image.
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Question 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 reason.
Answer:
The shopkeeper should fix the convex mirror. The convex mirror can form images of an object spread over a larger area.
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Question 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?
Answer:
Only real image is formed on the screen. So, if size of the real image formed by convex lens on screen is decreasing, it means that the object is moving away from the lens.
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Question 22:
Suppose we wish to obtain the real image of a distant tree. Explain two possible ways in which we can do it.
Answer:
Following are the two possible ways to obtain real image of distant tree :
1. By using a concave mirror and a screen.
2. By using a convex lens and a screen.
Because, both concave mirror and convex lens can form real image of distant object.
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Question 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.
Answer:
If the distance between an object and a lens decreases, the size of the image increases, it means the lens is convex lens.
Only real image can be obtained on screen. But, if the object is between focus and the pole of the lens, then the image formed will be virtual. And the virtual image can not be obtained on the screen. Hence, if we keep on decreasing the distance between the object and the convex lens, we would not be able to obtain the image on the screen.
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Question 24:
You are given three mirrors of different types. How will you identify each one of them?
Answer:
On analysing the image size and nature of image by moving the object towards or away from the mirrors given, we can assure the type of mirror. Following are the properties of the images formed by different mirrors:
(i) The plane mirror forms an erect image which is of the same size as the object. The image formed by the plane mirror cannot be obtained on a screen because the image formed by the plane mirror is virtual.
(ii) The concave mirror forms both a real as well as virtual image. The image can be smaller or larger in size than the object.
(iii) Convex mirror always produces virtual, erect and smaller images of the object.
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