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NCERT Class 10 Science Light – Reflection and Refraction: In-text questions (page 142) Solutions

AI-written, checked on 23 Oct 2026

Solutions written by Shishya, checked — not the board's official answers

Step-by-step working for every question of In-text questions (page 142) in NCERT's Class 10 Science book, chapter “Light – Reflection and Refraction”, written by Shishya. Each question is in our own short words; open the NCERT chapter for the exact wording and figures.

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  1. In-text (page 142) Q1

    Define the principal focus of a concave mirror.

    1. A concave mirror is a spherical mirror with a reflecting surface on the inner side.
    2. Consider parallel rays of light travelling along the principal axis towards the concave mirror.
    3. After reflection, these parallel rays converge at a single point on the principal axis.
    4. This point of convergence is called the principal focus of the concave mirror.
    5. The distance between the pole of the mirror and this point is the focal length.

    Answer: The principal focus of a concave mirror is the point on the principal axis where parallel rays of light, incident parallel to the principal axis, converge after reflection.

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  2. In-text (page 142) Q2

    A spherical mirror has radius of curvature 20 cm. What is its focal length?

    1. The radius of curvature (R) of the spherical mirror is given as 20 cm.
      why?

      For a spherical mirror the focal length is half the radius of curvature: f = R/2.

    2. The focal length (f) of a spherical mirror is half of its radius of curvature.
      why?

      For a spherical mirror the focal length is half the radius of curvature: f = R/2.

    3. Using the formula f = R / 2, we substitute the value of R.
      why?

      For a spherical mirror the focal length is half the radius of curvature: f = R/2.

    4. f = 20 cm / 2
    5. f = 10 cm

    Answer: 10 cm

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  3. In-text (page 142) Q3

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

    1. A concave mirror forms an erect and enlarged image when the object is placed between the pole and the focus.
    2. A convex mirror always forms an erect but diminished image, so it is not the answer.
    3. A plane mirror forms an erect image of the same size, so it is not the answer.
    4. Therefore, the mirror that gives an erect and enlarged image is a concave mirror.

    Answer: Concave mirror

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  4. In-text (page 142) Q4

    Why is a convex mirror preferred as a rear-view mirror in vehicles?

    1. A convex mirror is curved outward, causing light rays to diverge after reflection.
    2. This divergence allows the mirror to capture light from a wider area behind the vehicle.
    3. As a result, it provides a much wider field of view compared to a plane mirror.
    4. The image formed by a convex mirror is always virtual, erect, and diminished.
    5. The diminished size of the image ensures that objects at a distance appear smaller but still visible within the mirror's frame.
    6. This combination of a wide field of view and upright images makes it ideal for monitoring traffic behind a vehicle.
    7. Therefore, convex mirrors are preferred over plane or concave mirrors for this specific application.

    Answer: Convex mirrors are preferred because they provide a wider field of view and form erect, diminished images of distant objects.

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← Light – Reflection and Refraction: notes, practice and all exercises

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