MP Board Class 10 Science Chapter 10: The Human Eye and t…
MP Board Class 10 Science Chapter 10: The Human Eye and the Colourful World Important Questions — This chapter covers the structure and functioning of the human eye, defects of vision and their correction, dispersion of white light by a prism, atmospheric refraction, scattering of light, and the formation of rainbows. With 5–7 marks reserved in the MP Board Class 10 Science exam, this chapter is both fascinating and highly scoring. Below are the most important questions, previous year questions, and concept-based questions for 2027 board exam preparation.
📑 Table of Contents
👁️ 1. Structure of the Human Eye — Important Questions
Q1. Draw a labelled diagram of the human eye and explain the function of each part.
Answer: The human eye is roughly spherical with a diameter of about 2.3 cm. Key parts and their functions:
Q2. What is the power of accommodation of the eye? Explain with the help of ciliary muscles.
Answer: The power of accommodation is the ability of the eye lens to adjust its focal length so that objects at different distances can be seen clearly. When viewing distant objects, ciliary muscles relax, the lens becomes thin (increased focal length). When viewing nearby objects, ciliary muscles contract, the lens becomes thick (decreased focal length). The minimum distance for clear vision is 25 cm (near point) and the maximum is infinity (far point) for a normal eye.
Q3. Why does the pupil of the eye appear black? What happens to its size in bright and dim light?
Answer: The pupil appears black because light entering the eye is absorbed by the tissues inside (no light reflects back out). In bright light, the iris contracts the pupil (constricts) to reduce light entry — protecting the retina from damage. In dim light, the iris expands the pupil (dilates) to allow more light in — enabling better vision in darkness.
🔍 2. Defects of Vision and Correction
Q4. Explain myopia, hypermetropia, and presbyopia. How are they corrected?
📘 Key Formula: Power of lens P = 1/f (f in metres). For myopia, P is negative (concave lens). For hypermetropia, P is positive (convex lens). Unit: Dioptre (D).
Q5. A person cannot see objects clearly beyond 50 cm. What type of lens is needed? Calculate its power.
Answer: The person has myopia (can’t see beyond 50 cm). The correction requires a concave lens that forms the image of a distant object (at infinity) at the person’s far point (50 cm).
u = ∞, v = −50 cm = −0.5 m. Using lens formula: 1/f = 1/v − 1/u = 1/(−0.5) − 1/∞ = −2. ∴ P = 1/f = −2 D.
Therefore, a concave lens of power −2 D is required.
Q6. A person with hypermetropia has a near point of 75 cm. What corrective lens is needed?
Answer: The person cannot see objects closer than 75 cm. To see at 25 cm (normal near point), a convex lens is needed.
u = −25 cm = −0.25 m, v = −75 cm = −0.75 m.
1/f = 1/v − 1/u = 1/(−0.75) − 1/(−0.25) = −1.33 + 4 = +2.67.
P = 1/f = +2.67 D. Therefore, a convex lens of power +2.67 D is needed.
🌈 3. Dispersion and Rainbow Formation
Q7. What is dispersion of white light? Draw a diagram showing the dispersion of white light by a glass prism and explain.
Answer: Dispersion is the splitting of white light into its constituent colours (VIBGYOR) when it passes through a prism. This occurs because different colours have different wavelengths and the refractive index of glass varies with wavelength — violet deviates the most, red the least. The band of colours is called a spectrum.
Order of colours: Violet (λ ≈ 400 nm, highest deviation) → Indigo → Blue → Green → Yellow → Orange → Red (λ ≈ 700 nm, least deviation).
Q8. Explain the formation of a rainbow in the sky with a neat diagram.
Answer: A rainbow is a natural spectrum caused by dispersion, refraction, and total internal reflection of sunlight by water droplets in the atmosphere. The process involves three stages:
- Refraction: Sunlight enters the water droplet — slows down and bends, splitting into component colours (dispersion begins).
- Total Internal Reflection: The dispersed light hits the inner surface of the droplet at an angle greater than the critical angle — reflects internally.
- Second Refraction: Light exits the droplet, further separating colours. Red emerges at ~42°, violet at ~40° from the anti-sun direction.
The observer sees a circular arc of colours with red on the outer edge and violet on the inner edge. A secondary rainbow (with reversed colours: violet outer, red inner) may appear due to two internal reflections — it is fainter and at ~52°.
🌅 4. Atmospheric Refraction
Q9. Explain why stars twinkle but planets do not.
Answer: Stars appear as point sources of light. Their light passes through Earth’s atmosphere which has layers of varying density (and thus varying refractive index). This causes continuous refraction — the apparent position of the star fluctuates. The eye perceives these rapid fluctuations as “twinkling.” Planets, being much closer and appearing as extended disks (not point sources), have light coming from multiple points across their disk. The fluctuations from different points average out, so planets do NOT appear to twinkle.
Q10. Why does the Sun appear reddish at sunrise and sunset?
Answer: At sunrise and sunset, the Sun is near the horizon — its light travels through a thicker layer of the atmosphere (more distance through air). Blue light (shorter wavelength) is scattered more strongly than red light. By the time sunlight reaches our eyes, most blue light has been scattered away by atmospheric particles. Only the red light (longer wavelength, least scattered) reaches our eyes directly, making the Sun appear reddish-orange.
Q11. What is the apparent flattening of the Sun’s disc at sunrise and sunset due to?
Answer: Atmospheric refraction causes the lower edge of the Sun’s disc to appear more elevated than the upper edge (because light from the lower edge travels through more atmosphere). This makes the vertical diameter appear smaller than the horizontal diameter — the Sun appears oval or flattened. This is called “atmospheric refraction distortion.” In reality, the Sun is perfectly spherical.
💡 5. Scattering of Light
Q12. State and explain Rayleigh’s law of scattering. How does it explain the blue colour of the sky?
Answer: Rayleigh’s scattering law states that the intensity of scattered light ∝ 1/λ⁴ (inversely proportional to the fourth power of wavelength). This means:
- Violet/blue light (λ ≈ 400 nm) is scattered ~9× more than red light (λ ≈ 700 nm)
- During daytime, sunlight encounters atmospheric gas molecules — blue light scatters in all directions, giving the sky its blue appearance
- We see scattered blue light from all directions; the Sun itself appears slightly yellow (blue removed)
Q13. Why are danger signals red in colour? Explain.
Answer: Red light has the longest wavelength (≈700 nm) in the visible spectrum. According to Rayleigh’s law (scattering ∝ 1/λ⁴), red light is scattered the least by atmospheric particles. This means red light can travel through fog, smoke, rain, and mist with minimal scattering — it remains visible from the greatest distance. Hence, danger signals, traffic lights (red), and tail lights of vehicles use red to ensure maximum visibility in all weather conditions.
📝 6. Multiple Choice Questions (1 Mark Each)
These are the most frequently asked MCQs from MP Board exams.
- The least distance of distinct vision for a normal eye is:
(a) 25 cm ✓ (b) 30 cm (c) 50 cm (d) Infinity - Myopia is corrected by using:
(a) Concave lens ✓ (b) Convex lens (c) Bifocal lens (d) Cylindrical lens - The phenomenon of splitting of white light into seven colours is called:
(a) Dispersion ✓ (b) Refraction (c) Reflection (d) Scattering - Which colour of light deviates the most through a prism?
(a) Violet ✓ (b) Red (c) Yellow (d) Green - The scattering of light is proportional to:
(a) 1/λ⁴ ✓ (b) λ⁴ (c) 1/λ² (d) λ² - The colour of the sky from the surface of the moon would appear:
(a) Black ✓ (b) Blue (c) Red (d) White - Hypermetropia is corrected using which lens?
(a) Convex lens ✓ (b) Concave lens (c) Bifocal (d) Plano-concave - The part of the eye that controls the size of the pupil is:
(a) Iris ✓ (b) Cornea (c) Retina (d) Lens - Twinkling of stars is due to:
(a) Atmospheric refraction ✓ (b) Dispersion (c) Reflection (d) Scattering - Which type of lens is used in a simple microscope?
(a) Convex lens ✓ (b) Concave lens (c) Plane mirror (d) Bifocal lens
✏️ 7. Very Short & Short Answer Questions (2–4 Marks)
- What is the function of the iris in the human eye?
Controls the size of the pupil and regulates the amount of light entering the eye. (2 marks) - Define the far point and near point of a normal human eye.
Far point: Infinity. Near point: 25 cm. (2 marks) - Why does the sky appear dark instead of blue to an astronaut in space?
No atmosphere to scatter sunlight — scattering requires atmospheric particles. Space is dark because light travels straight without scatter. (3 marks) - What is a spectrum? How is it formed?
The band of seven colours (VIBGYOR) obtained when white light passes through a prism. Formed by dispersion due to wavelength-dependent refractive index. (2 marks) - Why is the colour of the sky blue?
Blue light has shorter wavelength, scattered ~9× more than red by air molecules (Rayleigh scattering). We see scattered blue light from all directions. (3 marks) - What is the power of a lens? Give its SI unit.
The ability of a lens to converge or diverge light. P = 1/f (in metres). SI unit: Dioptre (D). (2 marks) - Explain why the Sun is visible to us about 2 minutes before actual sunrise.
Atmospheric refraction bends sunlight upward — the Sun’s apparent position is higher than its actual position. This causes early sunrise (~2 min) and delayed sunset (~2 min). (3 marks) - What is the ciliary muscle? How does it help in vision?
Smooth muscle attached to the lens. Contracts to increase lens curvature (near vision), relaxes to flatten lens (distant vision). Enables accommodation. (3 marks)
📄 8. Long Answer Questions (5–6 Marks)
Q14. Draw a labelled diagram of the human eye and explain the process of seeing an object from the entry of light to the formation of an image on the retina.
Answer: Light from an object enters the eye through the cornea (most refraction occurs here) → passes through the pupil (size controlled by iris) → the crystalline lens fine-tunes focus → light rays converge on the retina → the retina’s photoreceptors (rods for dim light, cones for colour) convert light to electrical signals → optic nerve carries signals to the brain’s visual cortex → the brain interprets the image (which is formed inverted on the retina but perceived upright).
Q15. Explain the formation of a rainbow with a diagram. Why is a rainbow always seen with the Sun behind the observer?
Answer: A rainbow is formed when sunlight is refracted, internally reflected, and dispersed by water droplets in the atmosphere after rain. The observer must have the Sun behind them because light enters the droplet, undergoes total internal reflection (which reverses direction), and exits towards the observer. If the observer faces the Sun, the light would not be reflected back towards their eyes. The anti-sun direction (observer’s shadow) points to the centre of the rainbow arc. Rainbows appear as a complete circle when viewed from aeroplanes; from the ground, the horizon cuts off the bottom half.
Q16. Compare and contrast the three common defects of vision — myopia, hypermetropia, and presbyopia — in terms of causes, symptoms, and corrective lenses.
📋 Previous Year Questions (2018–2026)
❓ Frequently Asked Questions
Q1. What is the power of accommodation of the human eye?
It is the ability of the eye lens to adjust its focal length by changing its shape via ciliary muscles, enabling clear vision of objects at various distances.
Q2. What is the range of vision of a normal human eye?
From infinity (far point) to 25 cm (near point). Objects closer than 25 cm cannot be focused clearly.
Q3. What causes myopia? How is it corrected?
Caused by an elongated eyeball or excessive lens curvature, making the image form in front of the retina. Corrected using a concave (diverging) lens.
Q4. Why is a rainbow semicircular?
Rainbows are actually full circles, but the ground blocks the bottom half. When viewed from a high altitude (aeroplane, mountain top), a full circular rainbow can be seen.
Q5. Why do planets not twinkle?
Planets are extended sources (not point sources). Light from different points on a planet’s disk undergoes independent atmospheric fluctuations that average out — no net twinkling is observed.
Q6. What is the difference between refraction and dispersion?
Refraction is the bending of light when it passes from one medium to another. Dispersion is the splitting of white light into its constituent colours due to wavelength-dependent refractive index — a special case of refraction.
Q7. What is a bifocal lens? Who needs it?
A bifocal lens has two parts: the upper part (concave) for distance vision and lower part (convex) for reading. It is used by older people with presbyopia who also have myopia.
Q8. Why does the colour of the Sun appear white at noon?
At noon, sunlight travels the shortest path through the atmosphere. All colours reach our eyes with minimal scattering — the combination of all colours appears white or near-white.
Q9. What is the function of rods and cones in the retina?
Rods are sensitive to dim light — responsible for night vision (scotopic vision). Cones are sensitive to bright light and colour — responsible for daylight and colour vision (photopic vision).
Q10. What is the persistence of vision? How is it related to movies?
The eye retains an image for about 1/16th of a second after the object disappears. Movies (24 frames per second) exploit this — sequential still images appear as continuous motion.
Q11. What is the blind spot in the human eye?
The point on the retina where the optic nerve leaves the eye — it has no photoreceptors (rods/cones). Any image falling on this spot is not detected, creating a blind spot in our visual field.
Q12. What is Tyndall effect? How does it differ from Rayleigh scattering?
Tyndall effect is the scattering of light by suspended colloidal particles (like smoke, fog, dust). Rayleigh scattering is by molecules much smaller than λ (like air molecules). Tyndall effect is ∝ 1/λ² while Rayleigh is ∝ 1/λ⁴.