Causes of Myopia:
Myopia arises due to:

1. Excessive curvature of the eye lens, or
2. Elongation of the eyeball.

(a) Image formation by a myopic eye:

In a myopic eye, the image of a distant object is formed in front of the retina instead of on it.

```
Distant object → Eye lens → Image (formed in front of retina) ✗ Retina
```
(Ray diagram: parallel rays from distant object converge before the retina)

(b) Correction of myopia:

A concave lens of suitable power is used. It diverges the incoming rays so that they converge exactly on the retina.

```
Distant object → Concave lens → Eye lens → Image (on retina) ✓
```
(Ray diagram: concave lens diverges rays; eye lens then focuses them onto the retina)

Source: The Human Eye and the Colourful World, Section 10.2

---

• The question is 3 marks: ~1 mark for causes, ~1 mark for each diagram (described/drawn). Keep causes brief (2 points) and diagrams clearly labelled.
• Since this is a written exam, draw actual ray diagrams on paper with labels: "Retina," "Eye lens," "Image," and for correction — "Concave lens." The examiner specifically looks for the image forming in front of the retina (myopia) and on the retina (after correction).
• Never confuse myopia correction (concave lens) with hypermetropia correction (convex lens).

(b) Pupil

The pupil is the part of the human eye that allows light to enter into the eye by regulating and controlling the amount of light entering it.

Source: Chapter 10, Section 10.1 – The Human Eye

---

Although light first touches the cornea (which is technically the entry point and where most refraction occurs), the question asks specifically about the part that allows/regulates light entry — and the textbook explicitly states: "The pupil regulates and controls the amount of light entering the eye." The cornea is described as where refraction happens, not as the regulator of light entry. CBSE expects answer (b) Pupil based on this exact textbook line.

(b) Violet and Red

In dispersion by a prism, violet light bends the most and red light bends the least. The lower ray (P) is deviated more, so P is Violet; the upper ray (Q) is deviated less, so Q is Red.

Source: Light – Reflection and Refraction, Section 10.4 Dispersion of White Light by a Glass Prism

The key principle: violet deviates the most → appears at the bottom of the spectrum (lower emergent ray = P); red deviates the least → appears at the top (upper emergent ray = Q). The order from bottom to top is VIBGYOR. Examiners look for correct identification of both colours mapped to their positions in the diagram.

At very high altitudes, the atmosphere is very thin and there are very few particles present to scatter sunlight. Since scattering of light is not prominent at such heights, the blue colour (which is scattered by atmospheric particles near the earth's surface) does not reach the passengers' eyes. Hence, the sky appears dark to them.

Source: Chapter 10, Section 10.6.2 – Why is the colour of the clear Sky Blue?

---

• The key concept is scattering of light: fine atmospheric particles near the earth's surface scatter shorter (blue) wavelengths, making the sky appear blue.
• At very high altitudes, the atmosphere is very thin, so scattering is negligible → sky looks dark.
• The textbook directly states: "The sky appears dark to passengers flying at very high altitudes, as scattering is not prominent at such heights." Always use this line as the concluding statement.
• Examiners look for: mention of scattering, thin atmosphere/fewer particles, and the result (sky appears dark). Don't write about blue colour in detail — just connect its absence to why the sky looks dark.

Red light has the longest wavelength among all colours of visible light. Due to its long wavelength, red light is least scattered by fog, smoke, or dust particles in the atmosphere. Therefore, red light can travel the longest distance without significant loss of intensity and is visible clearly from far away. This makes red colour ideal for danger signals at airports and tall buildings, ensuring they are visible even in poor weather conditions.

Source: Chapter 10, Section 10.6 – Scattering of Light

The key concept here is scattering of light — shorter wavelengths (violet, blue) scatter more, longer wavelengths (red) scatter least. Examiners expect you to explicitly state: (1) red has the longest wavelength, (2) it is least scattered by fog/smoke, and (3) therefore visible from the greatest distance. Don't just say "red is not scattered" — say least scattered and link it to visibility from a distance. The textbook itself uses this example directly in Section 10.6.

(i) With age, the ciliary muscles weaken and the flexibility of the eye lens diminishes. This reduces the eye's ability to adjust its focal length (power of accommodation decreases), making it difficult to see both nearby and distant objects clearly.

(ii) The defect is called Presbyopia.

(iii) Such a person requires bi-focal lenses — upper part concave (for distant vision) and lower part convex (for near vision).

Ray diagram (Convex lens correcting near vision):

```
Object Convex lens Eye
| | \ |
---- rays ----( )-----> [Retina]
| /
```
(Convex lens converges rays so image forms on retina instead of behind it.)

Source: Chapter 10, Section 10.2(c) — Presbyopia

---

• (i) Always link the cause to ciliary muscles weakening + lens flexibility reducing — both points may be needed for full credit.
• (ii) The specific name Presbyopia is expected; writing only "old age defect" is insufficient.
• (iii) For the ray diagram, examiners look for: a convex lens, rays converging onto the retina, and labelling. Since the question says "type of corrective lens," a single clear diagram of the convex lens (near vision correction) with labels is acceptable. Mention bi-focal if space permits.

Path of emergent beam: The white light entering the prism splits into a band of seven colours — Violet, Indigo, Blue, Green, Yellow, Orange, Red (VIBGYOR) — on the screen PQ. Violet deviates the most and appears at the top (near P), red deviates the least and appears at the bottom (near Q).

Phenomenon: Dispersion of white light.

Cause: Different colours of white light bend through different angles while passing through the prism, because each colour travels at a different speed in glass. Violet bends the most and red the least.

Source: Chapter 10, Section 10.4 – Dispersion of White Light by a Glass Prism

---

• Examiners expect: (1) a correctly labelled diagram/trace showing the spectrum with VIBGYOR order, (2) the name "dispersion," and (3) the cause (different colours bend by different amounts / travel at different speeds in glass).
• A common mistake is reversing the order — remember violet is most deviated (bends toward the base more), so it appears lower on the screen if the prism apex points up. In the standard diagram with apex at top and screen to the right, violet is at the bottom (toward Q) and red at the top (toward P) — check the prism orientation in your diagram carefully before drawing.
• "VIBGYOR" must appear in your answer to show you know the colour sequence.

Tyndall Effect: When a beam of light passes through a smoke-filled room through a small hole, its path becomes visible due to scattering of light by colloidal particles. This phenomenon is called the Tyndall Effect. The smoke particles (colloidal size) scatter the light falling on them, making the beam's path visible to an observer on the side.

Dependence of colour on particle size:

• Very fine (small) particles scatter mainly blue light (shorter wavelengths).
• Particles of larger size scatter light of longer wavelengths (like red/yellow).
• If particles are very large, the scattered light may appear white.

Source: Chapter 10, Section 10.6.1 Tyndall Effect

---

• The question has two parts — name + explain the phenomenon (2 marks) and state colour dependence (1 mark). Allocate your writing accordingly.
• Always name the phenomenon first (Tyndall Effect), then explain it using key terms: scattering, colloidal particles, beam visibility.
• For colour dependence, examiners expect the three-point progression: fine particles → blue; larger particles → longer wavelengths; very large → white. Don't skip any.
• Avoid mixing up scattering with refraction or reflection — these are common errors.

A person is said to suffer from hypermetropia when they can see distant objects clearly but cannot see nearby objects distinctly (near point is farther than 25 cm).

Two causes:

1. The focal length of the eye lens is too long.
2. The eyeball has become too small, so light from nearby objects is focused behind the retina.

Correction: A convex lens (converging lens) of appropriate power is used.

Source: Chapter 10, Section 10.2 – Defects of Vision and their Correction

---

• The question has three parts (condition, causes, correction) but is only 2 marks — keep it brief and avoid excess detail.
• Examiners look for: the key symptom (cannot see nearby clearly), exactly two causes (focal length too long / eyeball too small), and the correct lens type (convex/converging).
• Do not confuse with myopia (concave lens). Hypermetropia = far-sighted = convex lens.

Option C — (A) is true, but (R) is false.

Assertion is correct, but the Reason is wrong: red light is least scattered (not most), so it travels farthest without losing intensity, making it visible from a large distance.

The textbook explicitly states: "The red is least scattered by fog or smoke. Therefore, it can be seen in the same colour at a distance." Blue light (shorter wavelength) is scattered the most. Students often confuse "visible from far" with "scattered the most" — actually the opposite is true. Least scattering = least loss of intensity = visible over greater distances.

The correct answer is (A) Refraction, dispersion and reflection.

Water droplets refract and disperse sunlight into its colours, then internally reflect it, and refract it again as it exits — forming a rainbow.

Source: Chapter 10, Section 10.4 Dispersion of White Light by a Glass Prism

---

The textbook explicitly states: "They refract and disperse the incident sunlight, then reflect it internally, and finally refract it again." The key word is internal reflection, not total internal reflection (which rules out option B). Option A uses the general term "reflection," matching the textbook language. Scattering (option C/D) plays no role in rainbow formation. Remember: the three phenomena are refraction + dispersion + (internal) reflection.

Ray Diagram:

```
Sunlight → [Enter droplet]
A (Dispersion - refraction at entry)
↘
B (Internal reflection at back of droplet)
↙
C (Refraction at exit)
→ Dispersed colours to observer's eye
```

Draw a circular water droplet. Mark:

• A – at the point where sunlight enters the droplet (dispersion occurs here)
• B – at the back surface inside the droplet (total internal reflection)
• C – at the point where light exits the droplet (second refraction)

Two necessary conditions to observe a rainbow:

1. The Sun should be behind the observer (rainbow forms in the direction opposite to the Sun).
2. Rain/water droplets must be present in the atmosphere in front of the observer.

Source: Chapter 10, Section 10.4 – Dispersion of White Light by a Glass Prism

---

• The textbook states that water droplets refract and disperse (A) → internally reflect (B) → refract again (C). Examiners expect all three labels correctly placed on the droplet diagram.
• The two conditions come directly from the text: Sun behind you, and water droplets (rain) in front. Many students forget to mention the Sun's position — this is a common mark-losing error.
• Since this is a diagram-based question, even a rough but correctly labelled sketch earns marks. Neatness and correct labelling of A, B, C are key.

Power of Accommodation: The ability of the eye lens to adjust its focal length to clearly see objects at different distances is called the power of accommodation.

Part responsible: The ciliary muscles play a major role in accommodation.

(i) Nearby objects: When focusing on nearby objects, the ciliary muscles contract, increasing the curvature of the eye lens. The lens becomes thicker, decreasing its focal length, thus forming a clear image on the retina.

(ii) Distant objects: When focusing on distant objects, the ciliary muscles relax, decreasing the curvature of the eye lens. The lens becomes thinner, increasing its focal length, thus forming a clear image on the retina.

Source: Chapter 10, Section 10.1.1 – Power of Accommodation

---

• Definition (1 mark): Must include "adjust focal length" and "different distances."
• Part named (½ mark): Ciliary muscles — not cornea, iris, or retina.
• Nearby & distant (1½ marks): Examiners look for the paired contrasts — contract/relax, thicker/thinner, focal length decreases/increases. All four terms should appear. Missing any pair costs marks.
• Keep sentences crisp; avoid repeating the definition when explaining each case.

(C) (A) is true, but (R) is false.

Assertion is correct — a myopic eye cannot see distant objects distinctly. However, myopia is corrected by a concave (diverging) lens, not a converging lens. Hence R is false.

Source: Chapter 10, Section 10.2(a)

---

The key fact to remember: Myopia → concave lens; Hypermetropia → convex (converging) lens. The Reason incorrectly states converging lenses for myopia — that correction applies to hypermetropia. Since A is true but R is false, the answer is (C). Do not confuse the two defects in assertion-reason questions.

(A) (a) and (b)

Wait — re-checking: Statement (a) ✓ (diameter ~2.3 cm), (b) ✓ (iris is a dark muscular diaphragm), (c) ✗ (most refraction occurs at the cornea, not the crystalline lens), (d) ✗ (ciliary muscles change the curvature/focal length of the lens, not the distance between lens and retina).

Correct answer: (A) (a) and (b)

• The passage explicitly states: "Most of the refraction for the light rays entering the eye occurs at the outer surface of the cornea" — so statement (c) is wrong.
• Statement (d) is wrong because in the human eye the lens-to-retina distance is fixed; it is the focal length (via curvature change by ciliary muscles) that adjusts, not the distance itself.
• Statements (a) and (b) are directly confirmed by the passage, making (A) the correct choice.

(i) The defect is Myopia (Short-sightedness).
Reason: In the diagram, the image is formed in front of the retina instead of on it, which is the characteristic feature of myopia.

(ii) Two causes of myopia:

1. Excessive curvature (increased converging power) of the eye lens.
2. Elongation of the eyeball (increase in the length of the eyeball).

(iii) Myopia is corrected by using a concave (diverging) lens of suitable power. It diverges the incoming rays so that they finally converge on the retina.

Corrective diagram:

```
Object → [Concave lens] → Eye lens → Image forms ON retina
```
(Diagram shows diverging rays from concave lens entering the eye and converging exactly on the retina.)

---

• The key visual clue is the image forming before the retina — this uniquely identifies myopia. Always state this reason explicitly.
• For causes, examiners expect the two standard textbook reasons: increased lens curvature AND elongated eyeball.
• For the correction diagram, draw the concave lens in front of the eye, show diverging rays, and label that the final image falls on the retina. Even a rough labelled sketch earns marks.
• Marks split: (i) 1 mark — name + reason; (ii) 1 mark — any two causes; (iii) 1 mark — correct lens named + diagram.

(c) Assertion (A) is true, but Reason (R) is false.

The Assertion is correct — rainbow is a natural spectrum of sunlight. However, the Reason is false because a rainbow is formed opposite to the Sun (not when the Sun is overhead) after a rain shower.

Source: Chapter 10, Section 10.4 — Dispersion of White Light by a Glass Prism

---

The key error in Reason (R) is the phrase "sun is overhead." The textbook clearly states that a rainbow is always formed in a direction opposite to that of the Sun. The sun being overhead is incorrect — the observer must have the Sun behind them. The presence of water droplets is correct, but since one part of the Reason is wrong, the whole Reason is false, making option (c) the right choice.

(d) Retina

The lens system of the human eye forms an image on the light-sensitive screen called the retina.

Source: Chapter 10, Section 10.1 – The Human Eye

---

The passage directly states: "Its lens system forms an image on a light-sensitive screen called the retina." Cornea is the transparent front membrane, ciliary muscles adjust the lens, and optic nerves carry signals to the brain — none of these is the image-forming screen. Just name the correct option and optionally add one supporting line for a 1-mark MCQ.

(a) The person is suffering from Hypermetropia (far-sightedness). A positive (+) power lens is a convex lens, used to correct this defect.

(b) Two causes of Hypermetropia:

1. The focal length of the eye lens is too long.
2. The eyeball has become too small.

(c) Given: Power, P = +2.0 D

Using $P = \dfrac{1}{f}$:

$$f = \frac{1}{P} = \frac{1}{+2.0} = +0.5 \text{ m}$$

The focal length of the lens is +0.5 m.

Source: Chapter 10, Section 10.2 (Hypermetropia); Chapter 9, Section 9.3.8 (Power of a Lens)

---

• The positive power directly tells you the lens is convex, which is used for hypermetropia — this is the key clue for part (a).
• For causes, use the exact two points from the textbook: eyeball too small OR focal length too long. Examiners award marks for these specific phrases.
• For part (c), the formula $f = 1/P$ is straightforward. Always state the unit (metres). Showing the substitution step earns full method marks even if you make an arithmetic slip.

A rainbow is a natural spectrum of colours appearing in the sky, caused by dispersion of sunlight by tiny water droplets present in the atmosphere.

After rainfall, tiny water droplets remain suspended in the atmosphere. These droplets act like small prisms — they refract, internally reflect, and refract the sunlight again, dispersing it into its seven colours (VIBGYOR). Hence, a rainbow is seen only after rainfall.

Source: Chapter 10, Section 10.4 Dispersion of White Light by a Glass Prism

---

• The question has two parts: define rainbow + explain why only after rainfall. Address both.
• Key terms examiners look for: dispersion, water droplets act as prisms, refraction + internal reflection + refraction.
• Mentioning VIBGYOR or "seven colours" adds value but is not compulsory for 2 marks.
• Keep it concise — 2 marks = ~2 key points, no elaborate diagrams needed unless asked.

(i) At very high altitudes, there are very few air molecules and fine particles to scatter sunlight. Since scattering is not prominent at such heights, the sky appears dark to passengers flying at very high altitudes.

(ii) Red light has the longest wavelength among visible colours and is least scattered by fog or smoke. Therefore, red danger signals can be seen clearly from a long distance without losing their colour.

Source: Chapter 10, Section 10.6 – Scattering of Light

---

• Both answers come directly from Section 10.6.2 of the textbook — quote those lines closely in the exam.
• For (i), the key phrase is "scattering is not prominent at very high altitudes" — no particles = no blue scattered light = dark sky.
• For (ii), the key idea is "red is least scattered", so it travels farther without being diffused, making it ideal for danger/warning signals.
• Examiners look for the word "scattering" in both answers — don't omit it.

(A) Iris

The iris is a dark muscular diaphragm that controls the size of the pupil, which in turn regulates the amount of light entering the eye.

Source: The Human Eye, Chapter 10, Section 10.1

---

Students often confuse iris and pupil here. The iris controls the pupil's size (it is the muscular structure doing the work), while the pupil is merely the opening through which light passes. The question asks what controls the amount of light — that is the iris. The pupil itself regulates light, but only because the iris changes its size. CBSE expects option (A) Iris as the answer based on the textbook wording.

(a) Since power P = –0.25 D (negative), the lens is a concave (diverging) lens.

Focal length: $f = \dfrac{1}{P} = \dfrac{1}{-0.25} = \mathbf{-4 \ m}$

(b) A concave lens is used to correct myopia (near-sightedness). A myopic eye can see near objects clearly but cannot focus on distant objects.

(c) For a concave lens, the image is always virtual, erect, and diminished, regardless of the object's position. So when the object is placed between F and 2F, the image formed is virtual, erect, and smaller than the object.

Source: Chapter 9, Sections 9.3.6, 9.3.8; Chapter 10

---

• Part (a): Negative power → concave lens. Use $f = 1/P$ directly; keep the negative sign.
• Part (b): Concave lenses diverge light, helping myopic eyes focus distant objects on the retina.
• Part (c): A concave lens always forms a virtual, erect, diminished image on the same side as the object, no matter where the object is placed — this is a key fact examiners test.
• Write the focal length with its unit (metres) and include the negative sign — both are award-worthy details.

Answer: B — Concave lens

Elongation of the eyeball causes myopia (near-sightedness). It is corrected by using a concave lens of suitable power.

Source: Chapter 10, Section 10.2(a) – Myopia

The key link is: elongated eyeball → myopia → concave lens. The passage explicitly states myopia "may arise due to…elongation of the eyeball" and "can be corrected by using a concave lens of suitable power." Students often confuse this with convex lens (used for hypermetropia). Remember: Myopia = concave; Hypermetropia = convex.

(i) A rainbow formed in the sky after rain is one natural instance where a spectrum of white light (dispersion) is observed.

(ii) White light splits into its seven constituent colours — Violet, Indigo, Blue, Green, Yellow, Orange, and Red (VIBGYOR) — on passing through the prism. This phenomenon is called dispersion of light.

(iii) Two conditions necessary to observe a rainbow:

1. The sun should be shining (presence of sunlight) and it should be at the observer's back.
2. Rain should be falling (water droplets must be present in the atmosphere) in front of the observer.

Source: Light – Reflection and Refraction / Human Eye and the Colourful World, NCERT Science Class 10

---

• (i) Any valid natural example of dispersion counts — rainbow is the most expected answer.
• (ii) Examiners want the term dispersion and the mention of VIBGYOR. Both together earn the mark.
• (iii) Two distinct, correctly stated conditions are needed for full 2 marks. The key points are: sunlight behind the observer + rain/water droplets in front. Avoid vague answers like "it should rain and be sunny."

Persons with presbyopia require bi-focal lenses.

A common bi-focal lens consists of both concave and convex lenses. The upper portion is a concave lens (for distant vision) and the lower portion is a convex lens (for near vision). This design is used because presbyopia patients often suffer from both myopia and hypermetropia simultaneously.

Source: Chapter 10, Section 10.2(c) – Presbyopia

---

• The key term examiners look for is bi-focal lenses — write it clearly.
• Mention both parts of the bi-focal lens with their positions (upper/lower) and functions (distant/near vision). These are two separate marking points.
• The reason (person suffers from both myopia and hypermetropia) earns the logic mark. Don't skip it.

Ray Diagram:

```
A
/\
/ \
/ \
P→ E →→→ F →S
/ \
B C
```

A ray PE is incident on face AB, refracts along EF inside the prism, and emerges as FS through face AC. The emergent ray FS bends towards the base of the prism compared to the original incident ray direction.

The angle between the incident ray (extended) and the emergent ray is called the angle of deviation (∠D).

(Diagram should show normals at E and F, angles ∠i, ∠r, ∠e, and ∠D marked clearly.)

Source: Chapter 10, Section 10.3 — Refraction of Light Through a Prism

---

• Examiners expect a labelled diagram showing: incident ray (PE), refracted ray (EF), emergent ray (FS), normals at both surfaces, and the angle of deviation ∠D marked between the extended incident ray and the emergent ray.
• The angle of deviation is the key term — must be named explicitly for full marks.
• The ray always bends towards the base of the prism; mentioning this can earn credit.
• Two marks: 1 for correct diagram with labels, 1 for naming the angle of deviation.

(d) Assertion (A) is false, but Reason (R) is true.

When ciliary muscles contract, the eye lens becomes thicker (not thin), decreasing focal length to focus nearby objects. However, Reason (R) is correct — ciliary muscles do control the power (focal length) of the eye lens.

Source: Chapter 10, Section 10.1.1 Power of Accommodation

---

The passage clearly states: "When you are looking at objects closer to the eye, the ciliary muscles contract. This increases the curvature of the eye lens. The eye lens then becomes thicker." So the Assertion is false — contraction makes the lens thick, not thin (the lens becomes thin when muscles are relaxed). The Reason is true since ciliary muscles change the curvature and hence the focal length (power) of the lens. This makes option (d) correct.

(a)
(i) Retina: It contains light-sensitive cells (rods and cones) that convert light into electrical signals, which are sent to the brain via the optic nerve, enabling vision.

(ii) Pupil: It controls the amount of light entering the eye by changing its size — it dilates in dim light and constricts in bright light.

(b) Ciliary muscles are attached to the eye lens. When viewing a nearby object, ciliary muscles contract, making the lens thicker (more convex) to increase its converging power. When viewing a distant object, the muscles relax, making the lens thinner (less convex) to decrease converging power. This adjustment of focal length is called accommodation.

---

• The question is from the chapter "The Human Eye and the Colourful World" (Ch. 11, Science Class 10).
• For part (a), name the specific function — don't just say "it helps in vision."
• For part (b), the key terms examiners look for are: contract/relax, thicker/thinner lens, and accommodation. Always link muscle action to lens shape change to focal length change.
• The source passages provided were from unrelated chapters, but this answer is based on the NCERT Class 10 Science Ch. 11 content as prescribed.

(a) The defect shown is Myopia (near-sightedness). The image of a distant object is formed in front of the retina instead of on it.

(b) Two causes:

1. Excessive curvature of the eye lens.
2. Elongation of the eyeball.

Corrective lens: A concave lens of suitable power is used to correct myopia, as it diverges light rays to bring the image back onto the retina.

Source: Chapter 10, Section 10.2 – Defects of Vision and their Correction

---

• The diagram clearly shows image forming in front of the retina → always Myopia.
• Examiners expect both causes listed separately for full marks.
• Name the corrective lens specifically as concave lens (diverging lens); just writing "lens" won't fetch marks.
• This is a 2-mark question but has three parts (identify + two causes + lens), so keep each point crisp — one line each.

From Earth, sunlight passes through the atmosphere where fine particles and air molecules scatter blue light (shorter wavelength) more strongly. This scattered blue light reaches our eyes, making the sky appear blue.

From space, there is no atmosphere to scatter sunlight. In the absence of scattering, the sky appears black.

Source: Chapter 10, Section 10.6.2 – Why is the colour of the clear Sky Blue?

---

• The key concept is scattering of light — fine atmospheric particles scatter shorter wavelengths (blue) more effectively.
• Two contrasting situations are asked: from Earth (atmosphere present → scattering → blue) and from space (no atmosphere → no scattering → black/dark).
• The passage directly states: "If the earth had no atmosphere, there would not have been any scattering. Then, the sky would have looked dark."
• Always mention shorter wavelength to justify why blue is scattered more — this earns the second mark.

(i) The defect shown is Myopia (near-sightedness). The image is formed in front of the retina instead of on it.

(ii) Two causes:

1. Excessive curvature of the eye lens.
2. Elongation of the eyeball.

(iii) A concave lens (diverging lens) of suitable power is used to correct myopia.

Source: Chapter 10, Section 10.2(a) – Myopia

---

• The diagram shows rays converging in front of the retina → this is the key identifier for myopia (not hypermetropia, where image forms behind the retina).
• Examiners specifically look for both causes stated clearly; missing one costs a mark.
• "Concave lens" must be named — writing only "diverging lens" may lose the mark if the term is not recognised as equivalent.
• This 2-mark question typically awards: 1 mark for defect + causes combined, 1 mark for corrective lens — so be concise and precise.

Scattering of light: When sunlight strikes fine particles in the atmosphere, the light gets redirected in different directions. This phenomenon is called scattering of light.

Blue sky: The fine particles and air molecules in the atmosphere are smaller than the wavelength of visible light. They scatter blue light (shorter wavelength) much more strongly than red light. This scattered blue light enters our eyes, making the sky appear blue.

Source: Chapter 10, Section 10.6.2

---

• Define scattering briefly (1 mark), then explain blue sky using the concept of wavelength-dependent scattering (1 mark).
• Key phrase: "shorter wavelengths (blue) are scattered more strongly."
• Avoid writing about Tyndall effect in detail — it wastes words here.
• Remember: red light has wavelength ~1.8 times greater than blue, so it scatters least — this is why the sky is blue, not red.

A rainbow appears in the sky after a rain shower, always in the direction opposite to the Sun.

It is caused by dispersion of sunlight by tiny water droplets in the atmosphere. The droplets refract and disperse sunlight, internally reflect it, and refract it again on exit, producing the VIBGYOR spectrum.

Ray Diagram:

```
Sunlight → [Water Droplet]
/ Refraction (dispersion)
/ Internal Reflection
/ Refraction (exit)
↓
Observer's Eye
(Violet at bottom, Red at top)
```

(Label: incident sunlight, refraction, internal reflection, dispersed colours — Red, Orange, Yellow, Green, Blue, Indigo, Violet)

Source: Chapter 10, Section 10.4 — Dispersion of White Light by a Glass Prism

---

• Examiners expect two facts: when (after rain shower) and where (opposite to the Sun) — both needed.
• The ray diagram must show a water droplet with labelled steps: refraction → internal reflection → refraction, and the emerging colour band (VIBGYOR). A neat labelled sketch earns the diagram mark.
• Avoid writing lengthy explanations; state the cause (dispersion by water droplets) briefly.

(c) Assertion (A) is true, but Reason (R) is false.

Assertion is correct — a myopic person cannot see distant objects clearly. However, myopia is corrected by a concave (diverging) lens, not a converging lens.

The textbook clearly states that myopia is corrected using a concave lens of suitable power. The Reason incorrectly states a converging lens is used, making R false. Since A is true and R is false, option (c) is correct. Remember: myopia → concave lens; hypermetropia → convex lens.

Dispersion of White Light:
The splitting of white light into its seven constituent colours (VIBGYOR) on passing through a prism is called dispersion.

Cause:
Different colours of light have different speeds in glass, so they bend through different angles on refraction. Violet bends the most and red bends the least, causing them to separate.

Diagram:

```
White light
|
___________\___________
| \ Glass Prism |
| \ |
|_______\______________|
\
\——— Violet
\—— Indigo
\— Blue
\- Green

• Yellow

Orange
Red
(Screen — VIBGYOR)
```

Source: Chapter 10, Section 10.4 — Dispersion of White Light by a Glass Prism

---

• Definition (1 mark): State that splitting of white light into VIBGYOR is called dispersion.
• Cause (1 mark): Different colours travel at different speeds in glass → different degrees of bending. Violet bends most, red bends least.
• Diagram (1 mark): Draw a triangular prism with a single white ray entering one face and seven colours (VIBGYOR order) emerging from the other face, fanning out onto a screen. Label "White light," the prism, and at least "Violet" and "Red" at the two ends of the spectrum.

(i) The defect shown is Hypermetropia (Far-sightedness). The part responsible is the eye lens — either its focal length is too long, or the eyeball is too small, causing the image to form behind the retina.

(ii) Two causes:

1. The focal length of the eye lens is too long.
2. The eyeball has become too small.

(iii) A convex (converging) lens is used to correct this defect. It provides the additional converging power needed to bring the image forward onto the retina, enabling clear near vision.

Source: Chapter 10, Section 10.2 (b) Hypermetropia

---

• The diagram shows rays focusing behind the retina → this is the key identifier for Hypermetropia (not Myopia, where rays focus in front).
• Examiners expect you to name the responsible part (eye lens/eyeball shape) and both causes explicitly.
• For the lens correction, say convex/converging and state its role (brings image onto retina) — both are needed for full marks.
• Do not confuse: Myopia → concave lens; Hypermetropia → convex lens.

(A) Red

Red light bends the least while passing through a glass prism, meaning it travels fastest in glass. Since refractive index $n = c/v$, higher speed means lower refractive index. Hence, refractive index of glass is minimum for red light.

Key concept: Refractive index is inversely related to the speed of light in the medium. In dispersion, violet bends the most (highest refractive index) and red bends the least (lowest refractive index). Remember: VIBGYOR — refractive index decreases from Violet to Red.

(B) Refraction, dispersion and internal reflection

Water droplets refract and disperse sunlight, then internally reflect it, and refract it again on exit, forming the rainbow.

Source: Chapter 10, Section 10.4 Dispersion of White Light by a Glass Prism

---

The textbook explicitly states: "They refract and disperse the incident sunlight, then reflect it internally, and finally refract it again when it comes out of the raindrop." The key word is internal reflection (not total internal reflection — option D also wrongly adds scattering). Option (A) says plain "reflection" which is incorrect. The correct phenomena are refraction + dispersion + internal reflection → Option (B).

Power of Accommodation: The ability of the eye lens to adjust its focal length to see objects clearly at different distances is called the power of accommodation.

Image distance: The image distance in the eye remains constant (image always forms on the retina). When the object distance increases, the eye lens adjusts its focal length so that the image is still formed on the retina.

Part responsible — Ciliary Muscles: When the distance of an object increases, the ciliary muscles relax, causing the eye lens to become thinner. This increases the focal length of the lens, allowing the distant object to be focused clearly on the retina.

Source: Chapter 10, Section 10.1.1 – Power of Accommodation

---

• Examiners expect three clear parts: definition, image distance behaviour, and explanation of ciliary muscles' role.
• A common mistake is saying image distance changes — it does NOT; it stays fixed at the retina. The focal length changes instead.
• Use key terms: relax, thinner, focal length increases — these fetch marks directly.

The lens of power −4.0 D is for the correction of distant vision (myopia), as it is a concave lens (negative power).

Its focal length:

$$f = \frac{1}{P} = \frac{1}{-4.0} = -0.25 \text{ m}$$

The focal length of the lens for distant vision is −0.25 m.

• In bifocal lenses for presbyopia, the concave (negative power) lens corrects distant vision (myopia) and occupies the upper portion; the convex (positive power) lens corrects near vision (hypermetropia) and occupies the lower portion.
• Use $f = \frac{1}{P}$ with $P$ in dioptres to get $f$ in metres. Don't forget the negative sign — examiners check it.

Answer: C — Blue

Very fine dust particles scatter mainly blue light (shorter wavelength) more strongly than light of longer wavelengths, as per the Tyndall effect.

Source: Chapter 10, Section 10.6.1 – Scattering of Light / Tyndall Effect

---

The key line from the textbook is: "Very fine particles scatter mainly blue light while particles of larger size scatter light of longer wavelengths." Since the question specifies very fine dust particles, the answer is blue. For MCQs, no explanation is needed in the exam — just the correct option letter and a one-line reason to be safe.

Rainbow: A rainbow is a natural spectrum of light appearing in the sky after a rain shower. It is caused by dispersion of sunlight by tiny water droplets in the atmosphere. The water droplets act like small prisms — they refract and disperse sunlight, reflect it internally, and refract it again on exit. It is always formed in the direction opposite to the Sun.

Diagram:

```
Sunlight
│
▼
┌─────────┐
│ Water │ ← Refraction + Dispersion
│ Droplet │ ← Internal Reflection
└─────────┘
│
▼
V I B G Y O R → Observer's Eye
(Violet bends most, Red bends least)
```

Labels: Sunlight (incident), Water droplet, Internal reflection, Dispersed colours (VIBGYOR), Observer's eye.

Source: Chapter 10, Section 10.4 (Dispersion of White Light by a Glass Prism)

---

• Definition (1 mark): Mention natural spectrum, rain shower, dispersion by water droplets.
• Mechanism (1 mark): Three steps — refraction + dispersion → internal reflection → refraction again on exit. Also note it forms opposite to the Sun.
• Diagram (1 mark): Show sunlight entering a circular droplet, internal reflection inside, colours emerging with VIBGYOR labelled. Violet at top (bends most), Red at bottom (bends least) in the actual rainbow arc.
• Examiners look for the word dispersion, internal reflection, and a neat labelled diagram. Don't skip any of the three optical steps.

Defect: Myopia (near-sightedness) — the student can read the nearby textbook... wait, the student cannot read the textbook but can see the distant blackboard clearly. This is Hypermetropia (far-sightedness).

Two reasons:

1. The focal length of the eye lens is too long.
2. The eyeball has become too small.

Corrective lens: Convex (converging) lens of appropriate power.

Source: Chapter 10, Section 10.2 — Defects of Vision and Their Correction

---

• Re-read the clue carefully: difficulty reading textbooks (nearby) but sees blackboard (distant) clearly → Hypermetropia, not myopia. A common exam trap is to misread this.
• If the question said difficulty seeing the blackboard but can read the textbook, the answer would be Myopia + concave lens.
• Examiners expect the defect name, both causes (exactly as listed in the textbook), and the lens type — all three parts must be present for full marks.

(C) blue

Very fine dust particles scatter light of shorter wavelengths most. Blue light has the shortest wavelength among the given options, so it is scattered the most.

Source: Chapter 10, Section 10.6.1 – Tyndall Effect

---

The key principle from the textbook: "Very fine particles scatter mainly blue light" (shorter wavelengths scatter more). This is the basis of the Tyndall effect. Red is scattered the least (which is why danger signals are red). In MCQs, eliminate red, orange, and yellow as they have longer wavelengths and scatter less.

(a) The phenomenon is called dispersion of light.

(b) White light is composed of seven colours (VIBGYOR). Each colour has a different wavelength and travels at a different speed in glass, so the prism bends (refracts) each colour by a different angle, splitting them into a band of seven colours.

(c)(i)

Experimental arrangement for recombination:

Two identical glass prisms P₁ and P₂ are placed with their bases in opposite directions (inverted with respect to each other).

• Prism P₁ disperses white light into seven colours (VIBGYOR).
• Prism P₂ acts as the recombining prism; it refracts each colour in the opposite direction.
• The colours recombine to give back white light on the screen.

Labelled Ray Diagram:

```
White light → [P₁] → VIBGYOR (spectrum) → [P₂ inverted] → White light → Screen
```
(P₁: dispersing prism; P₂: inverted prism; arrows show direction of rays)

Source: Light – Reflection and Refraction / Human Eye and the Colourful World, NCERT Class 10 Science

---

• (a) "Dispersion" is the one-word answer examiners expect. Do not write "refraction" alone.
• (b) Mention two things: white light has 7 colours + each colour refracts differently due to different wavelength/speed. Both points are needed for full credit.
• (c)(i) The key is the inverted second prism — this is the standard NCERT experiment. Draw a clear diagram with P₁, P₂ (inverted), spectrum between them, and white light emerging. Even a neat schematic diagram with labels earns marks; a missing diagram loses marks.

(B) presbyopia and bifocal lens

Presbyopia is caused by gradual weakening of ciliary muscles and diminishing flexibility of the eye lens (in old age), and it is corrected using bifocal lenses.

Source: Chapter 10, Section 10.2(c) – Presbyopia

The question directly describes the cause of presbyopia — weakening of ciliary muscles and reduced flexibility of the eye lens. The textbook states this defect is corrected by bifocal lenses (containing both concave and convex portions). Options A and C describe different defects entirely; Option D incorrectly pairs myopia with bifocal lenses.

(a) The eye defect shown is Myopia (Near-sightedness). In this defect, the image is formed in front of the retina instead of on it.

(b) Two causes of myopia:

1. Excessive curvature (elongation) of the eye lens.
2. Elongation of the eyeball.

(c) Myopia is corrected using a concave lens of suitable focal length.

Diagram:

```
Incoming [Concave] EYE
light rays → lens → ___
\ → ( | → / \
\ → | →| image|
/ → | → \___/ ← on retina
```

A concave lens diverges the light rays so that they converge exactly on the retina.

---

• The diagram in the question shows image forming in front of the retina → myopia. (If it were behind, it would be hypermetropia — read the diagram carefully in the exam.)
• For causes, always give two distinct biological/structural reasons — elongated eyeball and increased lens curvature are the standard NCERT answers.
• The correction diagram must show: parallel rays → concave lens → rays diverge → converge on retina. Draw and label clearly; examiners award 1 mark for the diagram alone.
• Part (a) is ~1 mark, (b) ~1 mark (½ each), (c) ~1 mark (diagram). Adjust if your paper allocates differently.

Rainbow is a natural spectrum formed in the sky after rain. Tiny water droplets in the atmosphere act as small prisms. Sunlight entering a droplet gets refracted, internally reflected, and refracted again on exit, causing dispersion into VIBGYOR (Violet to Red). Red bends least and appears at the top; Violet bends most and appears at the bottom.

Ray Diagram:

```
Sunlight → [Water Droplet]
Refraction → Internal Reflection → Refraction
→ Violet (bends most)
→ ...
→ Red (bends least)
```
(Diagram shows sunlight entering droplet, undergoing internal reflection, and emerging as a colour band.)

Source: Chapter 10, Section 10.4

---

• The question asks for any natural spectrum phenomenon — Rainbow is the best choice as it is directly explained in the textbook.
• Examiners expect: name of phenomenon + cause (water droplets acting as prisms) + sequence of events (refraction → internal reflection → refraction) + mention of VIBGYOR.
• Draw a neat labelled diagram showing a raindrop with an incoming white ray, internal reflection, and emerging coloured rays. Even a rough sketch earns the diagram mark.
• Key point: Rainbow is always seen opposite to the Sun.

(i) Very fine particles: They scatter mainly blue light (shorter wavelengths) more strongly. This is why the sky appears blue, as fine atmospheric particles scatter blue light towards our eyes.

(ii) Very large size particles: They scatter light of longer wavelengths. If the particles are large enough, the scattered light may even appear white.

Source: Chapter 10, Section 10.6.1 – Scattering of Light / Tyndall Effect

---

• The key line from the textbook is: "Very fine particles scatter mainly blue light while particles of larger size scatter light of longer wavelengths. If the size of the scattering particles is large enough, then, the scattered light may even appear white."
• Examiners expect both parts answered clearly with the colour/wavelength detail and a brief justification (e.g., sky appears blue / scattered light appears white).
• Avoid writing lengthy explanations — two crisp points with justification are sufficient for 2 marks.

(C) Colour of ray 1: Red; Colour of ray 2: Violet

Red light bends the least and violet bends the most while passing through a prism. So Ray 1 (less deviated) is red and Ray 2 (more deviated) is violet.

The key fact from the textbook (Section 10.4) is: "The red light bends the least while the violet the most." In a prism dispersion diagram, the ray closest to the original direction of white light is red, and the most deviated ray is violet. Examiners expect you to directly apply VIBGYOR and the deviation rule.

Scattering of Light: When light falls on fine particles (like dust, smoke, or air molecules), it is redirected in different directions. This phenomenon is called scattering of light. The colour of scattered light depends on the size of the particles; fine particles scatter blue light more strongly.

Difference from Reflection:

| Scattering | Reflection |
|---|---|
| Light is redirected in all directions by tiny particles | Light bounces back in a definite direction from a smooth surface |
| Occurs due to particles of various sizes (dust, molecules) | Occurs at a polished/smooth surface like a mirror |
| Does not follow strict laws | Follows the two laws of reflection strictly |

Source: Chapter 10, Section 10.6 Scattering of Light; Chapter 9, Section 9.1 Reflection of Light

---

• Examiners expect a definition of scattering followed by a clear comparison with reflection — either as a table or as labelled points.
• Key contrast: scattering = multidirectional, caused by particles; reflection = directional, caused by smooth surfaces following fixed laws.
• Mentioning the Tyndall effect or examples (blue sky, sunlight through smoke) can earn you extra credit but is not strictly required for 3 marks.
• Do not confuse scattering with diffuse reflection — scattering involves particles in a medium, not a rough surface.

In a myopic eye, the image of a distant object is formed in front of the retina instead of on it, due to excessive curvature of the eye lens or elongation of the eyeball.

A concave lens is a diverging lens. It diverges the incoming light rays before they enter the eye, effectively shifting the image backward onto the retina, thus restoring clear distant vision.

Source: Defects of Vision and Their Correction, Chapter 10

---

Examiners expect two clear points: (1) what goes wrong in myopia (image forms in front of retina) and (2) how a concave lens fixes it (diverges rays to push image back onto retina). Mentioning "diverging lens" earns terminology marks. Avoid lengthy diagrams unless asked — just state the cause and correction concisely.

When an object is far away, the ciliary muscles are relaxed, making the eye lens thin. Its focal length increases, enabling clear vision of distant objects.

When an object is close to the eye, the ciliary muscles contract, increasing the curvature of the lens, making it thicker. Its focal length decreases, enabling clear vision of nearby objects.

This ability of the eye lens to adjust its focal length is called accommodation.

Source: Chapter 10, Section 10.1.1 — Power of Accommodation

---

• Examiners expect two clear cases: distant object → relaxed muscles → thin lens → increased focal length; near object → contracted muscles → thick lens → decreased focal length.
• Always use the keyword accommodation — it fetches a mark.
• Keep it to 2–3 sentences covering both cases; no diagrams needed for 2 marks unless asked.

(B) Red, Yellow, Green, Blue, Violet

The correct sequence from top to bottom is: Red, Yellow, Green, Blue, Violet — since violet bends the most and red bends the least while passing through the prism.

Source: Chapter 10, Section 10.4 – Dispersion of White Light by a Glass Prism

---

The full spectrum is VIBGYOR (Violet, Indigo, Blue, Green, Yellow, Orange, Red). Violet deviates the most, so it appears at the bottom; Red deviates the least, so it appears at the top. Option (B) follows this order (a condensed ROYGBV sequence), making it correct. Students often confuse top/bottom — remember: least deviation = top (Red), most deviation = bottom (Violet).

(a) Ray diagram for refraction through a glass prism:

```
A
/\
/ \
i→ / \
─────/──────\─────
r│ │r'
│ │
─────\──────/──────
\ / →e
\ /
\/
B
```

Draw incident ray, refracted ray inside prism, and emergent ray.

• Angle of refraction (r): angle between the refracted ray inside the prism and the normal at the first surface.
• Angle of deviation (D): angle between the original direction of the incident ray and the direction of the emergent ray.

(b) When the path of the light ray is reversed, the angle of deviation remains the same.

This is because refraction is a reversible process. The reversed ray retraces the original path — it enters at the second surface and exits at the first — but the angle between the incident and emergent directions remains unchanged. The angle of deviation depends only on the angle of incidence and the prism, not on the direction of travel.

---

• Part (a) carries ~2 marks: draw a clear labelled diagram showing the incident ray, normal at both surfaces, refracted ray inside the prism, emergent ray, and mark r (angle of refraction at first surface) and D (angle of deviation). Label the prism clearly.
• Part (b) carries ~1 mark: the key fact is that the angle of deviation does not change because refraction is reversible. State the reason briefly.
• Examiners look for the correct labelling in the diagram and the correct conclusion (unchanged) with a one-line reason in part (b).

The old man cannot see objects closer than 1 m — his near point has receded. This is Presbyopia (or Hypermetropia). It is corrected by a convex (converging) lens.

Ray Diagram:

```
Object Convex Lens Eye
| | |
O ---rays----[( )]---------→ Retina
(lens refracts (image
rays to formed
converge) here)
```

The convex lens converges the rays from the nearby object so that they appear to come from a point farther away (≥ 1 m), allowing the eye to focus them on the retina.

Source: Chapter 10, Section 10.2 – Defects of Vision and their Correction

---

• The examiner expects you to identify the defect (Presbyopia/Hypermetropia) and name the corrective lens (convex lens) — 1 mark.
• A clear, labelled ray diagram showing the convex lens bending rays so the image falls on the retina — 1 mark.
• Key point: the lens virtually shifts the near object to the person's near point (1 m here), making it visible. Mention this briefly.
• Since diagrams are hard to draw in text, in the actual exam draw a proper eye diagram with the convex lens in front, showing diverging rays being converged onto the retina.

(i) To see nearby objects, the ciliary muscles contract, increasing the curvature (and thus the converging power) of the eye lens. This decreases the focal length of the lens, allowing a sharp image to be formed on the retina.

(ii) The power of accommodation of a normal human eye is approximately 4 dioptres. The near point is 25 cm and the far point is infinity.

• For (i), examiners expect mention of: ciliary muscles contracting → increased curvature → decreased focal length → clear image on retina.
• For (ii), the standard value is ~4 D (some texts state the range as 0 to 4 D). Mentioning near point (25 cm) and far point (infinity) adds completeness.
• Note: The source passages provided are from unrelated chapters; this answer is based on standard NCERT Class 10 Science Chapter 11 (Human Eye) content, as the question clearly belongs there.

(A) Converging lens

When the eyeball becomes too small, light focuses behind the retina (hypermetropia). A converging (convex) lens corrects this by converging rays to form the image on the retina.

Source: The Human Eye and the Colourful World, Section 10.2(b)

A reduced eyeball size causes hypermetropia (far-sightedness). The correction requires a convex/converging lens, not diverging. Bifocal is for presbyopia; cylindrical is for astigmatism. Examiners expect you to link "reduced eyeball → hypermetropia → converging lens."

Defect: Hypermetropia (Far-sightedness)

The person cannot read a book closer than 1 m, meaning the near point has shifted beyond 25 cm. This is Hypermetropia.

Cause: The image of a nearby object is focused behind the retina because the focal length of the eye lens is too long or the eyeball is too small.

Ray Diagrams:

Defect:

```
Object → [Hypermetropic Eye Lens] → Image formed BEHIND retina
```

Correction: A convex (converging) lens of suitable power is used. It converges the incoming rays so that the image falls exactly on the retina.

```
Object → [Convex Lens] → [Eye Lens] → Image ON retina
```

The convex lens provides the additional focusing power needed to bring the image onto the retina.

Source: Chapter 10, Section 10.2(b) — Hypermetropia

---

• The key clue is "cannot read closer than 1 m" — the near point is 1 m instead of the normal 25 cm. This directly indicates Hypermetropia, not myopia.
• Examiners award 1 mark for naming the defect, 1 mark for the defect diagram, and 1 mark for the correction diagram. Label diagrams clearly: show object, lens, retina, and where the image forms.
• Always state the corrective lens type and why it works (provides extra converging power).
• Do not confuse with Myopia (distant objects blurred, corrected by concave lens).

Answer: C

Assertion (A) is true, but Reason (R) is false. The spectrum is produced due to dispersion (different colours bend by different angles through refraction), not scattering. Red bends least and violet bends most because of dispersion by the prism.

• The Assertion is correct — white light splits into VIBGYOR on passing through a prism.
• The Reason is false because the cause is dispersion of light (different refractive indices for different colours), NOT scattering. Scattering explains phenomena like the blue sky, not the prism spectrum. Since the Reason is false, option C is correct.

Option A — Ciliary muscles of your eye contract and the eye lens becomes thick.

From section 10.1.1: when looking at nearby objects, ciliary muscles contract, increasing lens curvature, making it thicker, and decreasing focal length. "Relaxed" muscles make the lens thin (for distant vision) — eliminate B and D. Thin lens is for distant objects — eliminate C.

A rainbow is a natural spectrum formed in the sky after a rain shower. It is caused by dispersion of sunlight by tiny water droplets in the atmosphere. The water droplets act as small prisms. Sunlight entering a droplet is refracted and dispersed, then undergoes total internal reflection inside the droplet, and is refracted again while emerging. Due to dispersion, different colours (VIBGYOR) reach the observer's eye at different angles. A rainbow is always formed in the direction opposite to the Sun.

Ray Diagram:

```
Sunlight → [Water Droplet]
↗ Refraction (dispersion)
↘ Internal Reflection
↘ Refraction (exit)
→ Violet (inner arc) to Red (outer arc) → Observer's Eye
```

(Labelled diagram should show: incident sunlight, refraction at entry, internal reflection, refraction at exit, and emergent colours R, O, Y, G, B, I, V)

Source: Chapter 10, Section 10.4 Dispersion of White Light by a Glass Prism

---

• 3 marks = definition/cause (1 mark) + process inside droplet (1 mark) + diagram (1 mark).
• Key terms examiners look for: dispersion, refraction, internal reflection, water droplets act as prisms, opposite direction to Sun, VIBGYOR.
• The diagram must be labelled with at least: incident ray, refraction, internal reflection, emergent colours. A neat, labelled sketch earns the diagram mark even if not perfectly drawn.
• Do not confuse the order: Red is on the outer arc, Violet on the inner arc of the rainbow.

(C) Presbyopia

This defect arises due to the gradual weakening of the ciliary muscles and diminishing flexibility of the eye lens, usually occurring with ageing.

Source: Chapter 10, Section 10.2(c) – Presbyopia

---

The key phrase in the question — "gradual weakening of ciliary muscles and diminishing flexibility of eye lens" — is the textbook definition of Presbyopia. Myopia is caused by excessive curvature of the lens or elongation of the eyeball; Hypermetropia is caused by too long a focal length or a small eyeball. For a 1-mark MCQ, simply stating (C) Presbyopia with a one-line reason is sufficient.

(A) Iris and pupil

The iris controls the size of the pupil, and the pupil regulates the amount of light entering the eye.

The textbook explicitly states: "Iris is a dark muscular diaphragm that controls the size of the pupil. The pupil regulates and controls the amount of light entering the eye." Together, iris and pupil are responsible for admitting different amounts of light. Ciliary muscles change focal length, not light admission — a common confusion to avoid.