PHYSICS 10 CH10 LIGHT - NCERT EXERCISE QUESTION ANSWER
THE PHYSICS CAFE
CHAPTER TEN | LIGHT: REFLECTION
AND REFRACTION
Ncert Exercise Question Answer
Question 01: Which one of the following materials cannot be used to make a lens?
(a) Water
(b) Glass
(c) Plastic
(d) Clay
Answer: (d) Clay
Question 02: 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 centre of curvature
(b) At the centre of curvature
(c) Beyond the centre of curvature
(d) Between the pole of the mirror and its principal focus
Answer: (d) Between the pole of the mirror and its principal focus
Question 03: Where should an object be
placed in front of a 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 centre of the lens and its principal focus.
Answer: (b) At twice the focal length
Question 04: 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 concave
(b) Both convex
(c) The mirror is concave and the lens is convex
(d) The mirror is convex, but the lens is concave
Answer: (a) both concave
Question 05: No matter how far you stand from a mirror, your image appears erect. The mirror is likely to
be
(a) Plane
(b) Concave
(c) Convex
(d) Either plane or convex
Answer: (d) either plane or convex
Question 06: Which of the following lenses would you prefer to use while reading small letters found in a
dictionary?
(a) A convex lens of focal length 50 cm
(b) A concave lens of focal length 50 cm
(c) A convex lens of focal length 5 cm
(d) A concave lens of focal length 5 cm
Answer: (c) A convex lens of focal length 5 cm
Hint: Convex lens gives a large image of an object when it is placed between the
2f₁ and f₁ and magnification
is more for convex lenses having shorter
focal length.
Question 07: 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 distance
- Range of distance of the object from the mirror
must be less than 15 cm.
Hint: A concave mirror gives an erect image when an object is placed between its pole (P) and the
focus (F).
Nature of the image - The image formed will be Erect, Virtual and larger than object.
Question 08: Name the type of mirror used in the following situations
(a) Headlights of a car
(b) Side/rear-view mirror of a vehicle
(c) Solar furnace
Support your answer with reason.
Answer: (a) Concave
mirror
To get a powerful
parallel beam of light rays by placing bulb at focus. The shape of the
vehicle’s headlights are of concave type
(b) Convex
mirror
They are used as rear view (wing)
mirrors in vehicles that enables driver to view large area and erect image
(c) Concave mirror
To concentrate
sunlight at a small region to produce heat in solar furnaces.
Question 09: 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.
Answer: If one-half of a convex lens is covered with a black
paper even than the lens will form the complete image of the object.
In this case, a ray of light coming from the object will be refracted by the lower half of the lens and vice versa.
Question 10,
11,12,14,15 – to see this numerical click on this
video
Question 13: The
magnification produced by a plane mirror is +1. What does this mean?
Answer: hi
-v
Magnification = ___ =
___
ho
u
It means the
size of image formed is equal to the size of the object and the image formed is
erect.
Question 26: Find the focal length of a lens of power −2.0 D. What type of lens is this?
Answer: Given
Data: Power of lens P = -2.0 D
Power of lens is reciprocal of focal length.
P
= 1 / f
If
P = -2.0 D
Then f =
-.5 m
The negative
sign indicates the lens must have –ve focal length, so the lens is concave
lens.
Question 27: 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: Given
Data: Power of lens P = +1.5 D
Power of lens is reciprocal of focal length.
P
= 1 / f
If
P = +1.5 D
Then f =
1.66 m
The positive
sign indicates the lens must have +ve focal length, so the lens is convex lens
and convex lens is converging in nature
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