CBSE Science - Physics
Class X, Light - Reflection and Refraction
NCERT solutions (Textbook Exercise Questions)
Q.1: Which of the following materials can not be used to make a lens?
(a) water (b) glass (c) plastic (d) clay
Q.2: The image formed by a concave mirror is observed to be virtual, erect and larger than the object. Where should be the position of the object?
(a) between the principal focus and the center of curvature
(b) at the center of the curvature
(c) beyond the center of curvature
(d) between the pole of mirror and its principal focus.
Q.3: Where should an object be placed in front of convex lens to get a real image of the size of the object?
(a) at the principal focus of the lens
(b) at twice the focal length
(c) at infinity
(d) between the optical center of the lens and its principal focus.
Q.4: A spherical mirror and a thin spherical lens have each a focal length of –15 cm. The mirror and the lens are likely to be
(a) both are concave (b) both are convex (c) the mirror is concave and the lens is convex (d) the mirror is convex and but the lens is concave.
Q.5: No matter how far you stand from a mirror, our image appears erect. The mirror is likely to be –
(a) plane only (b) concave only (c) convex only (d) either plane or convex.
Q.6: Which one of the following lenses would you prefer to use while reading small letters found in a dictionary?
(a) A convex lens of focal 50 cm (b) A concave lens of focal 50 cm
(c) A convex lens of focal length 5 cm (d) A concave lens of focal length 5 cm.
Q.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.
Range of the distance of the object = 0 to 15 cm from the pole of the mirror.
Nature of the image = virtual, erect and larger than the object.
Q.8: Name the type of mirror used in the following situations –
(a) Head lights of a car (b) Side / rear-view mirror of vehicle (c) Solar furnace
Support your answer with reason.
Ans: (a) Concave mirror, (b) Convex mirror, (c) Concave mirror.
Reason: Concave mirrors are convergent mirrors. They converge the light incident on them to a single point i.e. at the principal focus and produce a large amount of heat at that point.
Q.9: One half of a convex lens is covered with a black paper. Will this lens produce a complete image of the object? Verify your answer experimentally. Explain your observations.
Ans: Yes, the lens will produce a complete image of the object although one half of a convex lens is covered with a black paper.
Experimental verification: A convex lens which is covered one half with a black paper is taken. Put an object before it and obtained an image on the screen by adjustment. There it can be observed that the lens produces the complete image of the object.
Explanation / Observation:
When the upper half of the lens is covered (as shown in the above figure) then rays of light incident from the object will be refracted by the lower half of the lens and meet at the other side of the lens to form a complete image of the object.
When the lower half of the lens is covered then rays of light incident from the object will be refracted by the upper half of the lens and meet at the other side of the lens to form a complete image of the object (as shown in the above figure).
Q.10: An object 5 cm in length is held 25 cm away from a converging lens of focal length 10 cm. Draw the ray diagram and find the position, size and the nature of the image formed.
h1 = 5cm, u = –25cm, f = + 10cm
Q.11: A concave lens of focal length 15 cm form an image of 10 cm from the lens. How far is the object placed from the lens? Draw the ray diagram.
Q.12: An object is placed at a distance of 10 cm from a convex mirror of focal length 15 cm. Find the position and nature of the image.
Q.13: The magnification produced by a plane mirror is +1. What does this mean?
Ans: The positive sign means image formed by a plane mirror is virtual and erect. Since the magnification is 1 it means that the size of the image is equal to the size of the object.
Q.14: An object 5 cm is placed at a distance of 20 cm in front of a convex mirror of radius of curvature 30 cm. Find the position, nature and size of the image.
Q.16: Find the focal length of a lens of power –2.0 D. What type of lens is this?
Q.17: A doctor has prescribed a corrective lens of power +1.5 D. Fined the focal length of the lens. Is the prescribed lens diverging or converging?
CBSE Class X NCERT Physics Chapter 10, Light - Reflection and Refraction
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