Wed. Jul 6th, 2022

# NCERT Solutions for Class 10 Science Chapter 10 Light Reflection and Refraction ## NCERT Solutions for Class 10 Science Chapter 10 Light Reflection and Refraction

Question 1
Define the principal focus of a concave mirror.
The principal focus of a concave mirror is a point on its principal axis to which all the light rays which are parallel and close to the axis, converge after reflection from the concave mirror.

Question 3
Name a mirror that can give an erect and enlarged image of an object.
Concave mirror.

Question 4
Why do we prefer a convex mirror as a rear-view mirror in vehicles?
We prefer a convex mirror as a rear-view mirror in vehicles because of two reasons :

a) A convex mirror always produces an erect image of the objects.

b) Convex mirror gives a wide field of view of the traffic behind. It enables the driver to view a larger area of the traffic behind him.

Q1. A ray of light traveling in the air enters obliquely into water. Does the light ray bend towards the normal or away from the normal? Why?

Ans: The light ray will bend towards the normal because air is a rarer medium and water is a denser medium.

Since light is traveling from rarer to a denser medium, So, it will bend towards the normal.

Question 5
The refractive index of a diamond is 2.42. What is the meaning of this statement?
The refractive index of a diamond is 2.42. This means that the speed of light in a diamond is 1/2.42 times the speed of light in a vacuum.

Question 1
Define 1 dioptre of power of a lens.
One dioptre is the power of a lens whose focal length is 1 meter.

Question 1
Which one of the following materials cannot be used to make a lens?
(a) Water
(b) Glass
(c) Plastic
(d) Clay
(d) Clay

Question 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 curvature
(c) Beyond the center of curvature
(d) Between the pole of the mirror and its principal focus.
(d) Between the pole of the mirror and its principal focus.

Question 3
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.
(b) At twice the focal length.

Question 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 concave.
(b) Both convex.
(c) the mirror is concave and the lens is convex.
(d) the mirror is convex, but the lens is concave.
(a) Both concave

Question 5
No matter how far you stand from mirror, your image appears erect. The mirror is likely to be
(a) plane
(b) concave
(c) convex
(d) either plane or convex.
(d) Either plane or convex.

Question 6
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.
(c) A convex lens of focal length 5 cm.

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.

A concave mirror gives an erect image when the object is placed between the focus F and the pole P of the concave mirror, i.e., between 0 and 15 cm from the mirror. The image thus formed will be virtual, erect and larger than the object.

Question 8
Name the type of mirror used in the following situations.
(b) Side/rear-view mirror of a vehicle.
(c) Solar furnace.
(a) Concave mirrors are used as reflectors in headlights of cars. When a bulb is located at the focus of the concave mirror, the light rays after reflection from the mirror travel over a large distance as a parallel beam of high intensity.

(b) A convex mirror is used as a side/rear-view mirror of a vehicle because

• A convex mirror always forms an erect, virtual and diminished image of an object placed anywhere in front of it.
• A convex mirror has a wider field of view than a plane mirror of the same size.

(c) Large concave mirrors are used to concentrate sunlight to produce heat in solar furnaces.

Question 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.