In-text Questions — Spherical Mirrors — Light - Reflection and Refraction

1. 11 markNCERT Cl-10 Science, In-text Qs after §9.2.2, Q1

   Define the principal focus of a concave mirror.

   Hint. Think about where parallel rays end up after hitting the mirror.

   Step 1 — Recall what happens to parallel rays. Rays travelling parallel to the principal axis converge to a single point on the axis after reflecting from a concave mirror.

   Step 2 — State the definition. Since this is where parallel rays consistently meet, this point is called the principal focus.

   ✦ Answer: The principal focus of a concave mirror is the point on the principal axis where light rays travelling parallel to the principal axis meet (converge) after reflection.

   Where students slip. Describing the focus as 'where the image forms' in general — the principal focus is specifically defined by parallel rays converging there, not by where any arbitrary object's image happens to form.

2. 21 markNCERT Cl-10 Science, In-text Qs after §9.2.2, Q2

   The radius of curvature of a spherical mirror is 20 cm. What is its focal length?

   Hint. There's a simple fixed ratio between radius of curvature and focal length for any spherical mirror.

   Step 1 — Recall the relationship. For a spherical mirror, the focal length is always half the radius of curvature: f = R/2.

   Step 2 — Substitute. f = 20/2 = 10 cm.

   ✦ Answer: 10 cm.

   Where students slip. Using f = R instead of f = R/2 — the focal length is specifically half the radius of curvature, not equal to it.

3. 31 markNCERT Cl-10 Science, In-text Qs after §9.2.2, Q3

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

   Hint. This only happens for one type of mirror, and only when the object is very close to it.

   Step 1 — Recall which mirror can enlarge at all. A convex mirror only ever gives diminished images, so it can't be the answer.

   Step 2 — Recall when a concave mirror gives an erect image. A concave mirror gives an erect, enlarged (virtual) image specifically when the object is placed between the pole and the focus.

   ✦ Answer: A concave mirror (with the object placed between the pole and the principal focus).

   Where students slip. Naming a convex mirror — convex mirrors always produce diminished images, never enlarged ones.

4. 42 marksNCERT Cl-10 Science, In-text Qs after §9.2.2, Q4

   Why do we prefer a convex mirror as a rear-view mirror in vehicles?

   Hint. Think about both the type of image formed and how much of the road behind is visible.

   Step 1 — Recall the image type. Convex mirrors always give an erect image, though diminished, regardless of how far the object is.

   Step 2 — Recall the field-of-view advantage. Since convex mirrors curve outward, they have a wider field of view than a plane mirror of the same size.

   Step 3 — Combine these into the practical benefit. Together, this lets the driver view a much larger area of traffic behind the vehicle than a plane mirror could show, which is why convex mirrors are preferred for safe driving.

   ✦ Answer: Convex mirrors always give an erect (if diminished) image and have a wider field of view than a plane mirror, letting drivers see a much larger area of traffic behind them.

   Where students slip. Mentioning only the wider field of view and forgetting the erect-image reason — both properties matter for the answer, not just one.

Solutions written by the tuition.in editorial team and checked against the NCERT Class 10 Science textbook, Reprint 2026-27 (jesc109.pdf) — four in-text question sets (14 questions total, not 18 as some older manifests claim) plus one end-of-chapter Exercise (17 questions, correctly counted). Total internal reflection (critical angle, optical fibres, mirage) has been removed from the current chapter.. Questions are referenced from the NCERT textbook for identification.