NCERT Class X Science Solutions: Chapter 10 – Light, Reflection and Refraction Part 2

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Question 6:

Which of the following lenses would you prefer to use while reading small letters found in a dictionary?

  1. A convex lens of focal length 50 cm

  2. A concave lens of focal length 50 cm

  3. A convex lens of focal length 5 cm

  4. A concave lens of focal length 5 cm

Answer:

C. A convex lens gives a magnified image of an object when it is placed between the radius of curvature and focal length. Also, magnification is more for convex lenses having shorter focal length. Therefore, for reading small letters, a convex lens of focal length 5 cm should be used.

Question 7:

We wish to obtain an erect image of an object, using a concave mirror of focal length 15 cm. What should be the range of distance of the object from the mirror? What is the nature of the image? Is the image larger or smaller than the object? Draw a ray diagram to show the image formation in this case.

Answer:

Range of object distance = 0 cm to15 cm

A concave mirror gives an erect image when an object is placed between its pole (P) and the principal focus (F).

Hence, to obtain an erect image of an object from a concave mirror of focal length 15 cm, the object must be placed anywhere between the pole and the focus. The image formed will be virtual, erect, and magnified in nature, as shown in the given figure.

As showing in images is a concave mirror.

Concave Mirror

Loading Image

Question 8:

Name the type of mirror used in the following situations.

  1. Headlights of a car

  2. Side/rear-view mirror of a vehicle

  3. Solar furnace

Support your answer with reason.

Answer:

  1. Concave

  2. Convex

  3. Concave

Explanation

  1. Concave mirror is used in the headlights of a car. This is because concave mirrors can produce powerful parallel beam of light when the light source is placed at their principal focus.

  2. Convex mirror is used in side/rear view mirror of a vehicle. Convex mirrors give a virtual, erect, and diminished image of the objects placed in front of it. Because of this, they have a wide field of view. It enables the driver to see most of the traffic behind him/her.

  3. Concave mirrors are convergent mirrors. That is why they are used to construct solar furnaces. Concave mirrors converge the light incident on them at a single point known as principal focus. Hence, they can be used to produce a large amount of heat at that point.