NCERT Class X Science Solutions: Chapter 10 – Light, Reflection and Refraction Part 5

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Question 15:

An object of size 7.0 cm is placed at 27 cm in front of a concave mirror of focal length 18 cm. At what distance from the mirror should a screen be placed, so that a sharp focused image can be obtained? Find the size and the nature of the image.

Answer:

Object distance,

Object height,

Focal length,

According to the mirror formula,

The screen should be placed at a distance of 54 cm in front of the given mirror.

The negative value of magnification indicates that the image formed is real.

The negative value of image height indicates that the image formed is inverted.

Question 16:

Find the focal length of a lens of power −2.0 D. What type of lens is this?

Answer:

A concave lens has a negative focal length. Hence, it is a concave lens.

Image result for concave lens ray diagram

Concave Lens Ray Diagram

Question 17:

A doctor has prescribed a corrective lens of power +1.5 D. Find the focal length of the lens. Is the prescribed lens diverging or converging?

Answer:

A convex lens has a positive focal length. Hence, it is a convex lens or a converging lens.

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