10. Human Eye and Colourful World Science class 10 in English Medium ncert book solutions Long Additional Questions With Solutions

Long Question with answer: 

Q1. A child while playing with his father's spectacles burnt a hole in a piece of paper by focusing a small image of sun on it. 

(i) What defect of vision his father is suffering from? 

(ii) Write two cause for this defect? 

(iii) Draw a ray diagram to show image formation by the defective eye?

(iv) Draw a ray diagram showing corrected eye using proper lens. 

Ans: 

(i) Hypermetropia

(ii) (a) the focal length of the eye lens is too long.

   (b) the eyeball has become too small.

(iii) Ray diagram to show image formation by the defective eye.

(iii) This defect can be corrolated by convex lens. 

Long Additional Questions with Solutions – Chapter 10: Human Eye and the Colourful World

Q1. Describe the structure and working of the human eye with the functions of its main parts.

Solution:

The human eye is a natural optical instrument that enables us to see objects by focusing light on the retina.

Main Parts and Their Functions:

• Cornea: The transparent front surface of the eye that refracts most of the incoming light.
• Iris: The coloured part of the eye that controls the amount of light entering the eye.
• Pupil: The opening in the iris through which light enters the eye.
• Eye Lens: A transparent convex lens that focuses light on the retina.
• Ciliary Muscles: Change the curvature of the eye lens for focusing objects at different distances.
• Retina: A light-sensitive screen where the image is formed.
• Optic Nerve: Carries visual signals from the retina to the brain.

Working:

Light enters through the cornea and pupil, passes through the eye lens, and is focused on the retina. The retina converts light into electrical signals, which are transmitted to the brain by the optic nerve. The brain interprets these signals as vision.

Q2. What is accommodation of the eye? Explain how the eye focuses on near and distant objects.

Solution:

Accommodation is the ability of the eye to change the focal length of its lens so that objects at different distances can be seen clearly.

For Distant Objects:

• Ciliary muscles relax.
• The eye lens becomes thin.
• The focal length increases.
• The image is formed on the retina.

For Near Objects:

• Ciliary muscles contract.
• The eye lens becomes thicker.
• The focal length decreases.
• The image remains focused on the retina.

Q3. Explain myopia and hypermetropia. Mention their causes and methods of correction.

Solution:

Myopia (Short-sightedness):

• A person can see nearby objects clearly but cannot see distant objects clearly.
• It is caused by an elongated eyeball or excessive curvature of the eye lens.
• It is corrected using a concave (diverging) lens.

Hypermetropia (Long-sightedness):

• A person can see distant objects clearly but cannot see nearby objects clearly.
• It is caused by a shorter eyeball or insufficient converging power of the eye lens.
• It is corrected using a convex (converging) lens.

Q4. What is presbyopia? Explain its causes and correction.

Solution:

Presbyopia is an age-related defect of vision in which a person cannot see nearby objects clearly.

Causes:

• Weakening of the ciliary muscles.
• Loss of flexibility of the eye lens with age.

Correction:

• It is corrected using convex lenses.
• If a person suffers from both myopia and hypermetropia, bifocal lenses are used.

Q5. Explain the phenomenon of dispersion of light. How is a rainbow formed?

Solution:

Dispersion is the splitting of white light into its seven constituent colours when it passes through a prism.

Different colours have different wavelengths, so they bend by different amounts. Violet deviates the most, while red deviates the least.

Formation of Rainbow:

• Sunlight enters tiny water droplets.
• It undergoes refraction and dispersion.
• It is internally reflected inside the droplets.
• It is refracted again while emerging.
• The observer sees a spectrum of seven colours called a rainbow.

Q6. Explain atmospheric refraction. Describe any three phenomena caused by it.

Solution:

Atmospheric refraction is the bending of light as it passes through different layers of the atmosphere having different densities.

Phenomena:

• Twinkling of Stars: Due to continuous atmospheric refraction, the apparent position and brightness of stars keep changing.
• Advance Sunrise and Delayed Sunset: The Sun appears about two minutes earlier before sunrise and remains visible for about two minutes after sunset.
• Apparent Flattening of the Sun: At sunrise and sunset, the lower part of the Sun appears raised more than the upper part, making the Sun appear flattened.

Q7. Explain the scattering of light. Why is the sky blue and sunrise/sunset reddish?

Solution:

Scattering of light is the phenomenon in which light is redirected in different directions by tiny particles present in the atmosphere.

Blue Colour of the Sky:

• Blue light has a shorter wavelength.
• It is scattered much more than red light.
• Therefore, the sky appears blue during the day.

Reddish Appearance at Sunrise and Sunset:

• Sunlight travels a longer distance through the atmosphere.
• Most of the blue light is scattered away.
• The red light reaches our eyes, making the Sun appear reddish.

Q8. Differentiate between myopia, hypermetropia and presbyopia.

Solution:

Q9. Explain cataract and its treatment.

Solution:

Cataract is a condition in which the eye lens becomes cloudy or opaque due to ageing or injury. It causes blurred vision and may lead to blindness if left untreated.

Treatment:

• The cloudy lens is removed by surgery.
• An artificial intraocular lens (IOL) is implanted in its place.
• Vision is restored after successful surgery.

Q10. Explain the importance of the human eye and the role of optical phenomena in daily life.

Solution:

The human eye is one of the most important sense organs, enabling us to observe the world around us. Its ability to accommodate, detect colours, and adjust to different light conditions helps us perform everyday activities efficiently.

Optical phenomena such as reflection, refraction, dispersion, atmospheric refraction, and scattering have many practical applications.

• Vision correction using spectacles and contact lenses.
• Formation of rainbows.
• Working of cameras, microscopes, and telescopes.
• Safe driving using rear-view mirrors.
• Understanding natural phenomena such as blue sky, twinkling stars, and red sunsets.

Thus, the study of the human eye and light helps us understand both biological vision and many natural and technological applications.

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