Human Eye & Colorful world Important Questions Class 10 Science

The human eye, a very delicate and intricate organ of vision, and the fascinating phenomena of the colourful world provide a deep understanding of optics, perception, and natural beauty. This chapter gets us deep into the workings of the human eye, defects of vision, and atmospheric optical phenomena. Let’s explore these CBSE Class 10 Ch 10 concepts in detail; keep reading and learning! 

The Human Eye: Structure and Function

The human eye is a spherical organ that enables us to perceive light, colour, and depth. This spherical organ serves as the primary sense organ for vision, allowing us to perceive light, colour, depth, and a vast array of visual details. It acts as a natural optical device, interpreting light and converting it into meaningful images the brain can understand.

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Chapter 10 Human Eye and Colourful World: Important Questions

1. Mars's atmosphere is composed mainly of carbon dioxide, nitrogen and argon and negligible amounts of oxygen, water vapour and methane.

Using the information given in the sentence above and knowledge about how rainbows are formed on Earth, explain why rainbow formation is impossible on Mars.

Answer: 

Rainbows on Earth are formed when sunlight is refracted, reflected, and dispersed in water droplets, resulting in a spectrum of colors. For a rainbow to form, there must be water vapor in the atmosphere to act as the medium through which the sunlight is refracted and dispersed.

On Mars, the atmosphere contains only trace amounts of water vapor, which is insufficient for the formation of rainbows. Without significant amounts of water droplets or vapor, there is no medium to refract and reflect light in the same way it occurs on Earth. Additionally, since Mars’s atmosphere is primarily composed of carbon dioxide, nitrogen, and argon, these gases do not have the same optical properties as water, and thus, they cannot create the dispersion of light required for a rainbow.

Therefore, rainbow formation is impossible on Mars due to the lack of water vapor in its atmosphere.

2. Space is mostly vacuum, devoid of any medium.

(a) What colour does the Sun appear to the astronauts on International Space Station? 

(b) Give reason for your answer to (a).

Answer: 

a) The Sun appears white to astronauts on the International Space Station (ISS).

(b) The reason the Sun appears white in space is that there is no atmosphere to scatter sunlight. On Earth, the atmosphere scatters shorter wavelengths of light (blue and violet), which is why the sky appears blue and the Sun appears yellowish or reddish when it is near the horizon. However, in space, without the scattering effect of the atmosphere, all wavelengths of light from the Sun reach the astronauts' eyes without distortion. As a result, the Sun appears white, which is the combination of all the colors of the visible spectrum.

3. A person's near point is at 45 cm and far point is at 2 m.

What kind of corrective lens is BEST suited for his vision defect?

a. Convex

b. Concave

c. Bifocal

d. Plano-convex

Answer:

(b) concave 

Explanation

The person's near point is at 45 cm, and their far point is at 2 m. This indicates that they have myopia (nearsightedness), as they can see objects up close but have difficulty seeing distant objects clearly. The corrective lens needed for myopia is a concave lens.

A concave lens helps diverge light rays entering the eye, shifting the image of distant objects closer to the retina, making it easier for the person to see clearly at a distance.

4. In a medium like glass, the velocity of light increases as the wavelength increases. Which of the following light would be the fastest in glass?

a. blue

b. violet

c. green

d. Red

Answer: (d) red

Explanation

In a medium like glass, the velocity of light increases as the wavelength increases. This is because the refractive index of a medium is inversely related to the wavelength of light, and shorter wavelengths (like violet and blue) are refracted more strongly, slowing down more than longer wavelengths (like red).

Given this, red light has the longest wavelength among the options, so it will travel the fastest in glass.

5. Which of the following correctly gives the sequence of events that take place when human eye changes its focus from a distant object to an object closer to the eye?

a. ciliary muscles relax --> curvature of eye lens increases --> focal length of eye lens increases

b. ciliary muscles contract --> curvature of eye lens decreases --> focal length of eye lens increases

c. ciliary muscles relax --> curvature of eye lens decreases --> focal length of eye lens decreases

d. ciliary muscles contract --> curvature of eye lens increases --> focal length of eye lens decreases

Answer:

‍(d)ciliary muscles contract --> curvature of eye lens increases --> focal length of eye lens decreases

Explanation

To focus on a near object, the ciliary muscles contract.

This causes the curvature of the eye lens to increase, making the lens more curved.

A more curved lens has a shorter focal length, allowing the eye to focus on nearby objects.

6. Which of these is a reason why a far-sighted person needs a convex lens to correct his vision?

a. The image forms in front of his retina

b. The image forms behind the retina.

c. The image forms below the retina.

d. The image forms on the retina.

Answer: 

(b) The image forms behind the retina.

Explanation

In far-sightedness, the eye's focal point is too far behind the retina, causing difficulty in focusing on nearby objects. A convex lens converges light rays before they enter the eye, allowing the image to form on the retina instead of behind it.

7. Under which of these can myopia and hypermetropia be classified?

a. breakdown of tissues

b. incorrect bending of light in the eye

c. incorrect reflection of light by surfaces around us

d. incorrect coordination with brain for colour

Answer: 

(b)incorrect bending of light in the eye

Explanation

Both myopia and hypermetropia are refractive errors, which occur due to the incorrect bending (or focusing) of light entering the eye. In myopia, the light is focused in front of the retina, while in hypermetropia, the light is focused behind the retina. Both conditions arise from the eye's inability to bend light correctly, often due to the shape of the eyeball or the lens.

Key Parts of the Eye:

1. Cornea: The transparent, curved outer layer that allows light to enter the eye and helps in refraction.
2. Iris: The coloured part of the eye that controls the size of the pupil and regulates the amount of light entering the eye.
3. Pupil: The central opening of the iris, acting as a window for light.
4. Lens: A convex, flexible structure that focuses light on the retina by adjusting its shape (accommodation).
5. Retina: The light-sensitive layer at the back of the eye containing rods (for dim light) and cones (for colour vision).
6. Optic Nerve: Transfers visual information from the retina to the brain.

Working of the Eye:

• Light enters through the cornea and passes through the pupil.
• The lens focuses the light onto the retina, forming an inverted image.
• The retina converts light into electrical signals, which the optic nerve sends to the brain, interpreting them as upright images.

Defects of Vision and Their Correction

Myopia (Nearsightedness):

• Cause: Elongation of the eyeball or excessive curvature of the lens causes light rays to focus in front of the retina.
• Symptoms: Difficulty in seeing distant objects clearly.
• Correction: Concave lenses diverge light rays, allowing them to focus correctly on the retina.

Hypermetropia (Farsightedness):

• Cause: Shortening of the eyeball or insufficient curvature of the lens causes light rays to focus behind the retina.
• Symptoms: Difficulty in seeing nearby objects clearly.
• Correction: Convex lenses converge light rays, enabling proper focus on the retina.

Presbyopia:

• Cause: Ageing reduces the flexibility of the lens, leading to difficulty in focusing on nearby objects.
• Symptoms: Commonly affects older adults.
• Correction: Bifocal lenses (with concave and convex segments) or progressive lenses.

Astigmatism:

• Cause: Uneven curvature of the cornea or lens leads to distorted or blurred vision.
• Correction: Cylindrical lenses correct the uneven refraction.

The Power of Accommodation

The lens's ability to adjust its focal length for viewing objects at various distances is known as accommodation. However, excessive strain can lead to conditions like eye fatigue.

Optical Phenomena in Nature

Dispersion of Light: When white light passes through a prism, it splits into its constituent colours, creating a spectrum. This occurs due to the varying refractive indices for different wavelengths of light.

Example: Formation of rainbows in nature.

Atmospheric Refraction: The bending of light as it passes through layers of the atmosphere with varying optical densities. 

Examples:

• Twinkling of Stars: Starlight undergoes continuous refraction due to atmospheric turbulence, making stars appear to twinkle.
• Apparent Sunrise and Sunset: The sun appears slightly above the horizon due to atmospheric refraction, even when it is below it.

Tyndall Effect: The scattering of light by particles in a colloidal solution or atmosphere. Examples:

• The bluish colour of the sky is due to the scattering of shorter wavelengths (blue) by atmospheric particles.
• The reddish appearance of the sun during sunrise and sunset is because the blue and green wavelengths scatter out, leaving longer wavelengths like red to dominate.

Total Internal Reflection in Rainbows: Rainbows form when sunlight undergoes refraction, internal reflection, and dispersion inside raindrops, producing a colourful arc in the sky.

Applications of Optical Principles

1. Optical Instruments: Cameras, projectors, and magnifying glasses utilise refraction and lens combinations for image formation.
2. Vision Correction: Eyeglasses and contact lenses correct defects like myopia and hypermetropia.
3. Fibre Optics: Principles of refraction and total internal reflection enable efficient light transmission for communication.
4. Astronomy: Telescopes use lenses and mirrors to study distant celestial objects, relying on the principles of reflection and refraction.

Tips for Preparing Chapter 10

By focusing on these strategies, you can master both the theoretical and practical aspects of Chapter 10 of CBSE Class 10 effectively:

1. Master the Eye’s Structure: Practice labelling diagrams of the eye and understand the function of each part, like the cornea, lens, retina, and optic nerve.
2. Focus on Vision Defects: Learn the causes, symptoms, and corrections for myopia, hypermetropia, presbyopia, and astigmatism.
3. Understand Atmospheric Phenomena: Study concepts like the twinkling of stars, the Tyndall effect, and the dispersion of light. Connect these to examples like rainbows and red sunsets.
4. Practice Ray Diagrams: Draw and label ray diagrams for refraction through lenses, light dispersion in prisms, and rainbow formation.
5. Solve Application-Based Questions: Work on numerical problems involving lens formulas, power of lenses, and critical angles. Solve CBSE sample and past papers for better preparation.
6. Regular Revision: Revise key topics and formulas regularly to strengthen your understanding.

CBSE Class 10 Chapter 10: The Human Eye and the Colourful World bridges fundamental optical principles with real-life applications and natural phenomena. A clear understanding of concepts like vision defects, atmospheric refraction, and dispersion equips students with insights into science and the natural world's beauty. Regular practice, focus on diagrams, and application-based learning can help master this engaging chapter. You got this! Happy learning!