In-text Questions — Mirror Formula — Light - Reflection and Refraction

1. 12 marksNCERT Cl-10 Science, In-text Qs after §9.2.4, Q1

   Find the focal length of a convex mirror whose radius of curvature is 32 cm.

   Hint. Same relationship as before — just watch the sign this time, since it's a convex mirror.

   Step 1 — Apply f = R/2. f = 32/2 = 16 cm.

   Step 2 — Assign the sign. Since the focus of a convex mirror lies behind the mirror (in the direction of the outgoing reflected light), its focal length is positive by the New Cartesian Sign Convention.

   ✦ Answer: f = +16 cm.

   Where students slip. Giving the focal length as −16 cm — that sign belongs to concave mirrors; a convex mirror's focal length is positive.

2. 23 marksNCERT Cl-10 Science, In-text Qs after §9.2.4, Q2

   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?

   Hint. A real image from a mirror always carries a negative magnification — use that to fix the sign of the magnification before solving.

   Step 1 — Assign signs. u = −10 cm (object distance is always negative). Since the image is real, the magnification must be negative: m = −3 (magnitude 3, for 'three times magnified').

   Step 2 — Use the magnification formula to find v. m = −v/u, so −3 = −v/(−10), which gives v = −30 cm.

   Step 3 — Interpret the sign of v. Since v is negative, the image is real and forms in front of the mirror, on the same side as the object.

   ✦ Answer: The image is located 30 cm in front of the mirror (real, inverted, magnified 3×).

   Where students slip. Using m = +3 because the problem says 'magnified' — magnified only refers to the size ratio; the sign of m still has to come from the image being real (negative m for mirrors), not from the word 'magnified' alone.

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.