The Human Eye and the Colourful World — Class 10 Physics NCERT Solutions (Free)
Free step-by-step NCERT solutions for Class 10 Physics chapter "The Human Eye and the Colourful World" — 10 important questions with detailed answers for CBSE board exam preparation.
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TL;DR: Free step-by-step NCERT solutions for Class 10 Physics chapter "The Human Eye and the Colourful World" — 10 important questions with detailed answers…
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Key Questions Covered:
- Define the 'power of accommodation' of the human eye. How does the human eye …
- A person cannot see objects distinctly beyond 2 meters. What kind of defect o…
- The near point of a hypermetropic person is 75 cm from the eye. What is the p…
- What is meant by the dispersion of white light? Draw a neat labelled diagram …
- Explain why stars twinkle, but planets do not.
- Why does the sky appear blue on a clear day?
- + 4 more questions in the full chapter
Solutions Summary:
| Question | Status |
|---|---|
| Define the 'power of accommodation' of the human eye. How… | ✓ Solved |
| A person cannot see objects distinctly beyond 2 meters. W… | ✓ Solved |
| The near point of a hypermetropic person is 75 cm from th… | ✓ Solved |
| What is meant by the dispersion of white light? Draw a ne… | ✓ Solved |
| Explain why stars twinkle, but planets do not. | ✓ Solved |
| Why does the sky appear blue on a clear day? | ✓ Solved |
Showing 6 of 10 questions
Q1: Define the 'power of accommodation' of the human eye. How does the human eye achieve it?
The 'power of accommodation' of the human eye is its ability to adjust the focal length of the eye lens to see objects clearly at varying distances. This is done by changing the curvature of the eye lens.
**How it is achieved:**
1. **For distant objects:** When the eye needs to see distant objects, the ciliary muscles relax. This makes the eye lens thinner and its focal length increases, allowing the light rays from distant objects to focus precisely on the retina.
2. **For nearby objects:**...
Q2: A person cannot see objects distinctly beyond 2 meters. What kind of defect of vision is he suffering from? What type of corrective lens should be used to restore proper vision? Calculate the power of the required lens.
1. **Defect of Vision:** The person cannot see distant objects clearly, which means he is suffering from **Myopia (nearsightedness)**.
2. **Corrective Lens:** Myopia is corrected using a **concave lens** (diverging lens) of appropriate focal length.
3. **Calculation of Power of the lens:**
* For a myopic eye, the far point is closer than infinity. Here, the person's far point is 2 meters.
* To correct this defect, the concave lens should form a virtual image of a distant object ...
Q3: The near point of a hypermetropic person is 75 cm from the eye. What is the power of the lens required to enable him to read clearly a book held at 25 cm from the eye?
1. **Defect of Vision:** The person's near point is 75 cm, which is further than the normal near point (25 cm). This indicates he is suffering from **Hypermetropia (farsightedness)**.
2. **Corrective Lens:** Hypermetropia is corrected using a **convex lens** (converging lens).
3. **Calculation of Power of the lens:**
* The book needs to be held at 25 cm (normal near point).
* Object distance, $u = -25$ cm $= -0.25$ m.
* The convex lens should form a virtual image of the bo...
Q4: What is meant by the dispersion of white light? Draw a neat labelled diagram to show the dispersion of white light by a glass prism. Name the seven colours of the spectrum.
**Dispersion of white light** is the phenomenon of splitting of white light into its constituent seven colours when it passes through a transparent medium like a glass prism. This happens because different colours of light have different wavelengths and thus travel at different speeds through the prism, causing them to bend (refract) at different angles.
**Diagram showing dispersion of white light by a glass prism:**
```
White Light
|\
| \ Incident Ray
...
Q5: Explain why stars twinkle, but planets do not.
The twinkling of stars and the non-twinkling of planets can be explained by the phenomenon of **atmospheric refraction** and the difference in their apparent sizes from Earth.
1. **Stars Twinkle:**
* **Point Sources:** Stars are extremely far away from Earth, so they appear almost as point sources of light to us.
* **Atmospheric Refraction:** The Earth's atmosphere is made up of layers of varying densities and temperatures. This causes the refractive index of the atmosphere to keep...
Q6: Why does the sky appear blue on a clear day?
The blue colour of the sky on a clear day is primarily due to the phenomenon of **scattering of light** by the tiny particles (molecules of air, dust particles, etc.) present in the Earth's atmosphere. This phenomenon is known as **Rayleigh scattering**.
Here's the explanation:
1. **Composition of White Light:** Sunlight, which appears white to us, is composed of different colours, each having a different wavelength (from violet to red).
2. **Scattering by Air Molecules:** The molecules of ai...
Showing 6 of 10 questions. Visit the full page for complete solutions.