NCERT Class VII Science Solutions: Chapter 15 – Light Part 4

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LONG ANSWER QUESTIONS

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:

  1. In first case we will use a concave mirror and a screen. As we know that a concave mirror forms a real image of a distant object at its focus, therefore, a real image of a distance tree will be formed on the screen placed at the focus of concave mirror.

  2. In second case, we will use a convex lens and a screen. As convex lens forms a real image of a distant object at its focus, therefore, a real image of a distant tree will be formed on the screen placed at the focus of convex lens.

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:

It is a convex lens.

No, when the object is placed close to a convex lens then the image formed is virtual which cannot be obtained on screen.

Question 24:

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

Answer:

We can identify the mirror by forming images of an object which are given as below:

  1. Plane mirror in case of plane mirror, image will be virtual, erect and of same size as that of object.

  2. Concave mirror in case of concave mirror, image may be real or virtual, inverted or erect and magnified or diminished depending upon the position of object.

  3. Convex mirror in case of convex mirror, image formed will always be virtual, erect and diminished in spite of the position of object.

    Image of Difference between plane mirror, concave mirror and convex mirror

    Difference between Plane Mirror, Concave Mirror and Convex Mirror

    Image of Difference between plane mirror, concave mirror and convex mirror