Human Eye and Colourful World — Previous Year Questions (Class 10 Science)
Light and the human eye's perception of color form the basis of visual science. Understanding refraction, dispersion, and eye defects helps explain natural
TL;DR: Light and the human eye's perception of color form the basis of visual science. Understanding refraction, dispersion, and eye defects helps explain na…
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Light and the human eye's perception of color form the basis of visual science. Understanding refraction, dispersion, and eye defects helps explain natural
Human Eye and Colourful World — Previous Year Questions with Solutions
Q (2023, 3 marks): Explain the structure of the human eye and describe the function of each major part.
Answer: Major parts of the eye:
1. Cornea: Transparent front layer that refracts light and provides most of the eye's focusing power.
2. Lens: Adjustable lens that fine-tunes focus by changing shape (accommodation).
3. Retina: Light-sensitive layer containing photoreceptor cells (rods and cones) that convert light into electrical signals.
4. Optic nerve: Transmits electrical signals from the retina to the brain.
5. Iris: Colored muscle that controls pupil size, regulating light entry.
6. Pupil: Opening controlled by iris that allows light to enter.
7. Vitreous humor: Gel-like substance that maintains eye shape and allows light to reach the retina.
Q (2022, 2 marks): What is accommodation of the eye? How does it enable us to see both near and distant objects clearly?
Answer: Accommodation is the ability of the lens to change its focal length by changing its shape.
For near objects (less than 25 cm):
- Ciliary muscles contract, lens becomes thicker and more convex.
- Focal length decreases, light from near objects focuses on the retina.
For distant objects (beyond 25 cm):
- Ciliary muscles relax, lens becomes thinner and less convex.
- Focal length increases, light from distant objects focuses on the retina.
The point closest to the eye at which an object can be seen clearly is called the near point (approximately 25 cm).
Q (2023, 3 marks): Distinguish between myopia and hypermetropia. How are these defects corrected?
Answer: Myopia (Short-sightedness):
- Distant objects appear blurred; near objects are clear.
- Caused by: Eyeball too long or cornea too curved.
- Image focuses in front of retina.
- Correction: Concave lens (negative power) spreads light rays outward before entering the eye.
Hypermetropia (Long-sightedness):
- Near objects appear blurred; distant objects are clear.
- Caused by: Eyeball too short or cornea too flat.
- Image would focus behind the retina.
- Correction: Convex lens (positive power) converges light rays inward before entering the eye.
Q (2022, 3 marks): What is dispersion of light? Explain why white light splits into a spectrum when passing through a prism.
Answer: Dispersion is the phenomenon where white light is separated into its constituent colors when passing through a medium like a prism.
Reason: Different colors have different wavelengths. When white light enters a prism:
1. Each color has a different refractive index in the prism material.
2. Red light (longest wavelength) bends least and has lowest refractive index.
3. Violet light (shortest wavelength) bends most and has highest refractive index.
4. This differential bending separates white light into a spectrum: VIBGYOR (Violet, Indigo, Blue, Green, Yellow, Orange, Red).
Q (2023, 3 marks): Explain why the sky appears blue during the day and red during sunset.
Answer: This is due to Rayleigh scattering of light by air molecules and dust particles.
Daytime (Sky is blue):
- Sunlight passes through the atmosphere at a small angle.
- Shorter wavelengths (blue light) scatter more than longer wavelengths.
- Scattered blue light reaches our eyes, making the sky appear blue.
Sunset (Sky is red):
- Sunlight travels a longer path through the atmosphere at a large angle.
- Most shorter wavelengths (blue, green) are scattered away before reaching the observer.
- Only longer wavelengths (red, orange) reach our eyes directly.
- The sky appears red or orange.
Q (2021, 2 marks): What is presbyopia? At what age does it typically develop and how can it be corrected?
Answer: Presbyopia is the age-related loss of elasticity of the lens, reducing the eye's ability to accommodate for near vision.
Age of onset: Typically develops after age 40.
Cause: With age, the lens protein becomes less flexible and ciliary muscles weaken.
Corrective measures:
1. Bifocal or progressive lenses: Different powers in different regions of the lens.
2. Separate reading glasses for near work.
3. Contact lenses with different prescriptions.
This condition affects nearly everyone as they age.
Frequently Asked Questions
What is the difference between a real image and a virtual image in the context of the eye?
The eye always forms a real, inverted image on the retina. The brain interprets this inverted image as upright. A virtual image is one that cannot be projected on a screen (like in a mirror or through a magnifying glass), which is different from how the eye processes images.
Why is ultraviolet light harmful to the eyes?
Ultraviolet (UV) light has shorter wavelengths and higher energy than visible light. Prolonged exposure can damage the cornea and lens, causing photokeratitis (temporary blindness) and cataracts (permanent clouding of the lens). UV-blocking sunglasses provide protection.
More Class 10 Science PYQs
- Chemical Reactions and Equations
- Light (Reflection and Refraction)
- Electricity
- Acids, Bases and Salts
- Metals and Non-metals
- Life Processes
🤖 Stuck on any of these? Ask Syllab's free AI Tutor to explain step by step →