Here in this post we provided NCERT Exemplar Problem Class 7 Science Light Chapter 13 Full Explanation by group of Science Experts. We have provided here each questions answer with reason behind the answer.
Hope it help you!
Light Class 7 Exemplar full Explanation:
-
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.
Answer:- c) plane mirror and convex mirror.
Mirrors of Boojho is plane mirror and paheli’s mirror is Convex mirror.
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:- a) concave mirror only.
Concave mirror can form real image.
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) 2m
b) 1m
c) 0.5 m
d) 0.25 m
Answer:-b) 1 m
The distance between the object and the image formed by plane mirror is 1 m .
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:- b) concave mirror or convex lens.
To obtain an enlarged image concave mirror or Convex lens can be used.
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:- b) when the sun is behind you.
Rainbow can be seen when the sun is behind you.
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:- b) only a concave mirror.
An erect and enlarged image can be form by only concave mirror.
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:- c) Both concave mirror and convex lens.
We can get an inverted image by both concave mirror and Convex lens.
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:- b) concave lens provided the image is smaller than object.
Erect image formed by the given is concave lens and image is smaller than object.
-
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.
Answer:- The image formed by the given lens is always virtual , erect and smaller in size for an object kept at different positions in front of it, that is the image is formed by the concave lens . Concave lens always form the smaller , erect and virtual image for the object.
10) Fill in the blanks :
a) The inner surface of a steel spoon acts as a ______________ mirror.
Answer:- the inner surface of a steel spoon acts as a concave mirror.
b) The outer surface of a flat steel acts as a ____________mirror.
Answer:- The outer surface of a flat steel acts as a plane mirror.
c) The outer surface of a round bottom steel bowl acts as a ___________ mirror.
Answer:- the outer surface of a round bottom steel bowl acts as a convex mirror.
d) The inner surface of the reflector of a torch acts as a _____________ mirror.
Answer:- the inner surface of the reflector of a torch acts as a concave mirror.
11) State whether the following statements are True or false.
a) A concave lens can be used to produce an enlarged and erect image.
Answer:- False
Concave lenses are used to produce and smaller and erect image.
b) A convex lens always produces a real image.
Answer:- False
A convex lens can form real and inverted image.
c) The sides of an object and it’s image formed by a concave mirror are always interchanged.
Answer:- True
d) An object can be seen only if it emits light.
Answer:- False.
An object can be seen only if it does not emit light.
-
Short Answer Questions
12) What type of mirror is used as a side mirror in a scooter ? Why is the type of mirror chosen ?
Answer:- The mirrors used as the side mirror of the scooter in which the image of the object appear smaller than the real object. Because the type of mirror used in the side mirror of scooter and car is convex mirror. It can also form the images of an object over a large area. Therefore it helps the driver while driving the car or scooter to see the traffic behind him.
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 ?
Answer:- The nature of the lenses A and B are
A = convex lens
B= 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.
Answer:- No. Light made by the laser torch is not able to emit different colours of light. As laser torch gives out only one colour of light. Thus when fall on prism a band of seven colours will not be observed by boojho.
15) State the correct sequence (1-7) of colours in the spectrum formed by the prisms A and B , shown in figure 15.2.
Answer:- The correct sequence of the colours in the spectrum formed by the prism A and B is ,
16) The side mirror of a scooter got broken. The mechanic replaced it with a plane mirror. Mention any inconveniences that the driver of the scooter will face while using it ?
Answer:- the mirrors which are used in the side mirror of the car or scooter are generally convex mirrors . In Convex Mirror the obtained image of the all object is smaller as compared to real object and Convex mirror covers the larger area so that the traffic behind the car or scooter should be seen to the driver while driving. But in the plane mirror the image form is erect and of same size of the object it will be clearly come in the small mirror while driving thus driver will not be able to see the traffic behind him while driving the scooter.
17) The concave reflecting surface of a torch got rusted. What effect would this have on the beam of light from the torch ?
Answer:-
The rusted reflecting surface of the co concave mirror will not allow to the total beam of light from the torch . The beam of light will be diffused with only small intensity. As the rusted part of concave surface will show reflection of light falling on it and small intensity of light will pass through it.
18) An erect and enlarged image of an object is formed on a screen . Explain how this could be possible.
Answer:-
Here, we have obtained an image which is erect and enlarged on a screen. This is possible when we place an object between F and 2F of the lens, in the upside down position. Then we get the erect and enlarged image on screen.
19) Two different type of lenses are placed on a sheet of newspaper. How will you identify them without touching ?
Answer:-
If there are two different types of lenses placed on sheet of newspaper,
looking through the lens to the newspaper, if letters appear bigger than the original letters are then the lens is convex lens.
If looking through the lens to the newspaper letters appear smaller than the original letters on newspaper then the 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 reason.
Answer:-shopkeeper should fix a convex mirror. It will give the maximum view of his shop. Convex mirror form the image over the large area spread. And thus the maximum view will be obtained by it.
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:- As given in question, during the distance between the object and Convex lens is changing, size of the image formed on the screen is decreasing then in that case the object is moving away from the lens placed there.
-
Long Answer Questions
22) Suppose we wish to obtain the real image of a distance tree. Explain two possible ways in which we can do it.
Answer:- If we want to get an real image of a distance tree then, we can use the combination of screen and lens also the screen and a mirror for that. If the tree is at far distance then for obtaining the image we can use convex lens with screen by which we get a real image of that tree.
Also we can use a concave mirror and screen in which also we get the same real image for the distance tree.
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:- When the distance between an object and a lens decreases, the size of the image increases, this is obtained by using the convex lens.
If we still keep on decreasing the distance between the object and lens, then we will not be able to obtain the image on the screen, because if we keep an object close to the lens than the image we get is virtual which is not obtained on the screen thus we will not be able to obtain it.
24) You are given three mirrors of different types. How will you identify each one of them?
Answer:-
If we take three different types of mirrors we can identify each of them by obtaining an image on the mirrors with the help of object.
An image formed by the plane mirror is erect, virtual, and of same size of the object. Image form at the same distance. Left side of object will appear on right side in plane mirror and right side of object will appear on left side of mirror.
An image formed by the concave mirror is real and inverted. If the object is placed to close to the mirror then the concave mirror will give virtual, erect and magnified image.
An image formed by the convex mirror will be virtual, erect and smaller in size as than the object given.
Thus how we can find out the three mirrors by finding out the type of image on it.