NCERT Class VII Science Solutions: Chapter 15 – Light Part 3

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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, laser torch gives out light of only one colour.

Question 15:

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

As showing in images is a spectrum formed by the prisms A and B. (Q)

Spectrum Formed by the Prisms a and B. (Q)

As showing in images is a spectrum formed by the prisms A and B. (Q)

Answer:

As showing in images is a spectrum formed by the prisms A and B. (A)

Spectrum Formed by the Prisms a and B. (A)

As showing in images is a spectrum formed by the prisms A and B. (A)

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:

The driver will not be able to see traffic spread over a large area behind him.

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:

The beam of light will be diffused with lower intensity.

Question 18:

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

Answer:

The image formed on the screen could be enlarged and erect if the object is placed upside down between F and 2F of the lens.

Question 19:

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

Answer:

If the letters appear bigger/magnified, then the lens is a convex lens. If the letters appear smaller, then the lens will be concave lens.

Image of difference between concave and convex lens

Difference between Concave and Convex Lens

Image of difference between concave and convex lens

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:

He will fix a convex mirror because it can form images of object spread over a large area.

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:

The object is moving away from the lens.

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