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light- refraction, reflection questions, Exercises of Physics

Physics

NCERT science light chapter of physics related best practice exercises and questions with diagrams

Typology: Exercises

2024/2025

Available from 05/22/2025

mratheist095
mratheist095 🇮🇳

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NCERT Solutio
n
s for Class
10
Science Chapter
10
Light Reflection and Refraction
095 notes
Questions Page: 168
1. Define the principal focus of a concave mirror.
Answer-
Light rays that are parallel to the principal axis of a concave mirror converge at a specific point on its principal axis
after reflecting from the mirror. This point is called the principal focus of the concave mirror.
2. The radius of curvature of a spherical mirror is 20 cm. What is its focal length?
Answer-
Radius of curvature (R) = 20 cm
Radius of curvature of the spherical mirror = 2 × Focal length (f) R
= 2f
f= R/2 = 20 / 2 = 10
Therefore, the focal length of the spherical mirror is 10 cm.
3. Name the mirror that can give an erect and enlarged image of an object. Answer-
The mirror that can give an erect and enlarged image of an object is a Concave Mirror.
4. Why do we prefer a convex mirror as a rear-view mirror in vehicles?
Answer-
A convex mirror is preferred as a rear-view mirror in cars and vehicles as it gives a wider field of view, which helps the
driver see most of the traffic behind him. Convex mirrors always form an erect, virtual, and diminished image of the
objects placed in front of it.
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095 notes Light Reflection and Refraction

Questions Page: 168

  1. Define the principal focus of a concave mirror. Answer- Light rays that are parallel to the principal axis of a concave mirror converge at a specific point on its principal axis after reflecting from the mirror. This point is called the principal focus of the concave mirror.
  2. The radius of curvature of a spherical mirror is 20 cm. What is its focal length? Answer- Radius of curvature (R) = 20 cm Radius of curvature of the spherical mirror = 2 × Focal length (f) R = 2f f= R/2 = 20 / 2 = 10 Therefore, the focal length of the spherical mirror is 10 cm.
  3. Name the mirror that can give an erect and enlarged image of an object. Answer- The mirror that can give an erect and enlarged image of an object is a Concave Mirror.
  4. Why do we prefer a convex mirror as a rear-view mirror in vehicles? Answer- A convex mirror is preferred as a rear-view mirror in cars and vehicles as it gives a wider field of view, which helps the driver see most of the traffic behind him. Convex mirrors always form an erect, virtual, and diminished image of the objects placed in front of it.

095 notes Light Reflection and Refraction

Questions Page No: 171

  1. Find the focal length of a convex mirror whose radius of curvature is 32 cm. Answer- Radius of curvature (R) = 32 cm Radius of curvature = 2 × Focal length (f) R= 2f f = R/2 = 32/2 = 16 Therefore, the focal length of the given convex mirror is 16 cm.
  2. A concave mirror produces three times magnified (enlarged) real image of an object placed at 10 cm in front of it. Where is the image located? Answer- Magnification produced by a spherical mirror: Object distance (u) = – 10 cm v = 3 × (- 10) = – 30 cm Therefore, the negative sign indicates that an inverted image is formed in front of the given concave mirror at a distance of 30 cm.

095 notes Light Reflection and Refraction

Ice 1.31 – –

Water 1.33^ Rock salt^ 1.

Alcohol 1.36 – –

Kerosene 1.44 Carbon disulphide 1.

Fused quartz 1.46^ Dense

flint glass

Turpentine oil 1.47 Ruby 1.

Benzene 1.50 Sapphire 1.

Crown

glass

1.52 Diamond 2.

Answer- Lowest optical density = Air Highest optical density = Diamond The optical density of a medium is directly related to its refractive index. A medium with the highest refractive index will have the highest optical density and vice-versa. It can be observed from the table that air and diamond, respectively have the lowest and highest refractive index. Hence, air has the lowest optical density and diamond has the highest optical density.

095 notes Light Reflection and Refraction

  1. You are given kerosene, turpentine and water. In which of these does the light travel fastest? Use the information given in the table.

Material medium

Refractive index Material medium Refractive index

Air 1.0003 Canada Balsam 1.

Ice 1.31 – –

Water 1.33^ Rock salt^ 1.

Alcohol 1.36 – –

Kerosene 1.44 Carbon disulphide 1.

Fused quartz

1.46 Dense

flint glass

Turpentine oil 1.47^ Ruby^ 1.

Benzene 1.50 Sapphire 1.

095 notes Light Reflection and Refraction

Questions Page No: 184

  1. Define 1 dioptre of power of a lens. Answer- Dioptre is the SI unit of power of lens is denoted by the letter D. 1 dioptre can be defined as the power of a lens of focal length 1 metre.
  2. A convex lens forms a real and inverted image of a needle at a distance of 50 cm from it. Where is the needle placed in front of the convex lens if the image is equal to the size of the object? Also, find the power of the lens. Answer- The position of the image should be at 2F since the image is real and the same size. It is given that the image of the needle is formed at a distance of 50 cm from the convex lens. Therefore, the needle is placed in front of the lens at a distance of 50 cm. Object distance (u) = – 50 cm Image distance, (v) = 50 cm Focal length = f According to the lens formula,

095 notes Light Reflection and Refraction

  1. Find the power of a concave lens of focal length 2 m. Answer- The focal length of the concave lens (f) = 2 m Power of lens (P) = 1/f = 1/ (-2) = - 0.5D Questions Page No: 185
  2. Which one of the following materials cannot be used to make a lens? (a) Water (b) Glass (c) Plastic (d) Clay Answer – (d) Clay cannot be used to make a lens because if the lens is made up of clay, the light rays cannot pass through it.
  3. 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

095 notes Light Reflection and Refraction

Questions Page No: 186

  1. 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) The mirrors are likely to be either plane or convex

095 notes Light Reflection and Refraction

  1. 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 – (b) A convex lens of focal length 5 cm can be used while reading small letters found in a dictionary
    1. 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 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.
    2. 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 a reason. Answer- (a) Concave Mirror: Concave mirrors can produce a powerful parallel beam of light when the light source is placed at their principal focus. (b) Convex Mirror: Because of its largest field of view. (c) Concave Mirror: Because it concentrates the parallel rays of the sun at a principal focus.
    3. One-half of a convex lens is covered with black paper. Will this lens produce a complete image of the object? Verify your answer experimentally. Explain your observations. Answer- Yes, it will produce a complete image of the object, as shown in the figure. This can be verified experimentally by observing the image of a distant object, like a tree on a screen, when the lower half of the lens is covered with black paper. However, the intensity or brightness of the image will reduce.
    4. 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 nature of the image formed.

095 notes Light Reflection and Refraction

Image distance, v= – 10 cm According to the lens formula, The negative value of u indicates that the object is placed 30 cm in front of the lens. This is shown in the following ray diagram.

  1. 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. Answer- Focal length of convex mirror (f) = +15 cm Object distance (u) = – 10 cm According to the mirror formula,

095 notes Light Reflection and Refraction

The image is located at a distance of 6 cm from the mirror on the other side of the mirror. The positive and a value of less than 1 magnification indicates that the image formed is virtual, erect, and diminished.

  1. The magnification produced by a plane mirror is +1. What does this mean? Answer- The positive sign means an 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.
  2. 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. Answer- Object distance (u) = – 20 cm Object height (h) = 5 cm Radius of curvature (R) = 30 cm Radius of curvature = 2 × Focal length R = 2f f = 15 cm According to the mirror formula,

095 notes Light Reflection and Refraction

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

  1. Find the focal length of a lens of power - 2.0 D. What type of lens is this? Answer- Power of lens (P) = 1/f P = - 2D f = - 1/2 = - 0. m A concave lens has a negative focal length. Therefore, it is a concave lens.
  2. 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- Power of lens (P) = 1/f P = 1.5D f = 1/1.5 = 10/15 = 0.66 m A convex lens has a positive focal length. Therefore, it is a convex lens or a converging lens.

095 notes Light Reflection and Refraction