In-text Questions — Defects of Vision — Human Eye and Colourful World

1. 12 marksNCERT Cl-10 Science, In-text Qs after §10.2, Q1

   What is meant by power of accommodation of the eye?

   Hint. Think about what the ciliary muscles are actually adjusting, and why that adjustment is needed at all.

   Step 1 — Recall what changes inside the eye. The ciliary muscles can change the curvature of the eye lens, which changes its focal length.

   Step 2 — Explain why this matters. Since objects at different distances need different focal lengths to be focused sharply on the retina, this adjustment is what lets the eye see both near and distant objects clearly.

   ✦ Answer: The power of accommodation is the eye's ability to adjust the focal length of its lens (by changing its curvature via the ciliary muscles) so that objects at different distances can all be focused clearly on the retina.

   Where students slip. Describing accommodation as the eye 'moving' to focus — nothing physically moves position; it's the lens's curvature (and hence focal length) that changes, not its location.

2. 23 marksNCERT Cl-10 Science, In-text Qs after §10.2, Q2

   A person with a myopic eye cannot see objects beyond 1.2 m distinctly. What should be the type of the corrective lens used to restore proper vision?

   Hint. The lens needs to make a distant object's image appear to come from exactly the person's own far point.

   Step 1 — Identify the defect and the lens type. A far point nearer than infinity is myopia, corrected using a concave (diverging) lens.

   Step 2 — Set up the values. The lens must form a virtual image of an object at infinity exactly at the person's far point: u = −∞, v = −1.2 m.

   Step 3 — Apply the lens formula. 1/v − 1/u = 1/f, so 1/f = 1/(−1.2) − 0 = −1.2⁻¹, giving f = −1.2 m.

   ✦ Answer: A concave lens of focal length 1.2 m (power ≈ −0.83 D) is needed.

   Where students slip. Prescribing a convex lens — myopia (near-sightedness) always needs a diverging concave lens, never a converging one.

3. 31 markNCERT Cl-10 Science, In-text Qs after §10.2, Q3

   What is the far point and near point of the human eye with normal vision?

   Hint. One of these two values is a distance in centimetres; the other isn't a finite distance at all.

   Step 1 — Near point. The near point (least distance of distinct vision) for a normal young adult is about 25 cm.

   Step 2 — Far point. The far point of a normal eye is infinity, since a normal eye can relax its lens enough to focus parallel rays from arbitrarily far away.

   ✦ Answer: Near point ≈ 25 cm; far point = infinity.

   Where students slip. Giving a finite number for the far point — a normal eye's far point is specifically infinity, not some large but finite distance.

4. 42 marksNCERT Cl-10 Science, In-text Qs after §10.2, Q4

   A student has difficulty reading the blackboard while sitting in the last row. What could be the defect the child is suffering from? How can it be corrected?

   Hint. The blackboard is far away — think about which defect specifically affects distant vision.

   Step 1 — Identify the defect. Difficulty seeing something far away (the blackboard), while presumably reading a nearby book without trouble, is the signature of myopia (near-sightedness).

   Step 2 — State the correction. Myopia is corrected using a concave lens of suitable power, which diverges the incoming light so that the image forms exactly on the retina instead of in front of it.

   ✦ Answer: Myopia — corrected with a concave lens of appropriate power.

   Where students slip. Diagnosing hypermetropia — that defect affects near vision, not distant vision like reading a blackboard from the back of the class.

Solutions written by the tuition.in editorial team and checked against the NCERT Class 10 Science textbook, Reprint 2026-27 (jesc110.pdf) — one in-text question set (4 questions, not 10 as some older manifests claim) plus one end-of-chapter Exercise (12 questions, not 17). Unchanged by rationalisation; the chapter describes the retina generically (no rods/cones, blind spot or fovea named) and never uses the term 'Rayleigh scattering.'. Questions are referenced from the NCERT textbook for identification.