CBSE Class 10 Science Chapter 11 Human Eye MCQs with Answers
FAQs on CBSE Class 10 Human Eye MCQ for Practice
1. What are the important functions of the iris, pupil, and ciliary muscles in the human eye?
These parts are crucial for vision control and focus. The key functions as per the CBSE Class 10 syllabus are:
- Iris: It is a muscular diaphragm that controls the size of the pupil, thereby regulating the amount of light that enters the eye.
- Pupil: This is the adjustable opening in the centre of the iris that allows light to pass through to the lens and retina.
- Ciliary Muscles: These muscles are responsible for changing the shape and focal length of the eye lens. This process, known as accommodation, allows the eye to focus on objects at different distances.
2. What is myopia (near-sightedness) and what are its two possible causes? How is this defect corrected?
Myopia is a common vision defect where a person can see nearby objects clearly but cannot see distant objects distinctly. In this condition, the image of a distant object is formed in front of the retina.
The two main causes are:
- Excessive curvature of the eye lens.
- Elongation of the eyeball.
Correction: Myopia is corrected by using a concave lens of an appropriate power. This lens diverges the incoming light rays, allowing the eye's lens to focus the image correctly onto the retina.
3. Why do stars appear to twinkle while planets do not? Explain this important concept.
This phenomenon is caused by atmospheric refraction of light.
- Twinkling of Stars: Stars are extremely distant, so they act as point-sized sources of light. As starlight enters the Earth's atmosphere, it passes through layers of air with varying densities and temperatures. This causes the light to refract continuously and randomly, making the apparent position of the star shift and the amount of light entering the eye flicker. This results in the twinkling effect.
- Why Planets Don't Twinkle: Planets are much closer to Earth and are considered extended sources (a collection of many point sources). While the light from each point on the planet also refracts, the twinkling effects from all these points average out and nullify each other. This results in a steady, non-twinkling appearance.
4. Explain the phenomenon of dispersion of white light through a glass prism. What is a spectrum?
When a beam of white light passes through a glass prism, it splits into its seven constituent colours. This splitting of light is known as dispersion. A spectrum is the band of colours produced, typically in the order: Violet, Indigo, Blue, Green, Yellow, Orange, and Red (VIBGYOR). This occurs because different colours of light travel at slightly different speeds in the glass and bend at different angles. Violet light bends the most, and red light bends the least.
5. How does the defect of hypermetropia differ from myopia? What type of lens is used to correct it?
Hypermetropia (far-sightedness) is the opposite of myopia (near-sightedness). Here are the key differences:
- Vision Defect: In hypermetropia, a person can see distant objects clearly but finds it difficult to see nearby objects. In myopia, the opposite is true.
- Image Formation: For a person with hypermetropia, the image of a nearby object is formed behind the retina. In myopia, the image of a distant object is formed in front of the retina.
- Correction: Hypermetropia is corrected using a convex lens of suitable power, which converges the light rays to form the image on the retina. Myopia is corrected using a concave lens.
6. Why does the sun appear reddish during sunrise and sunset? Is this an important question for the board exam?
Yes, this is a frequently asked question. The reddish appearance of the sun at sunrise and sunset is due to the scattering of light by particles in the Earth's atmosphere.
- At Sunrise/Sunset: The sun is near the horizon, and its light must travel through a thicker layer of the atmosphere to reach our eyes. During this long path, most of the shorter wavelength light, such as blue and violet, is scattered away by air molecules. The longer wavelength light, like red and orange, is scattered the least and is able to reach our eyes, giving the sun its reddish appearance.
- At Noon: When the sun is overhead, the light travels a much shorter distance through the atmosphere, so less light is scattered and the sun appears white.
7. What is meant by the power of accommodation of the eye? How does this power get affected in old age, leading to presbyopia?
The power of accommodation is the unique ability of the eye lens to adjust its focal length, allowing us to see both distant and nearby objects clearly. This adjustment is made by the ciliary muscles, which alter the curvature of the lens.
In old age, the ciliary muscles often weaken, and the eye lens loses some of its flexibility. This diminishes the eye's ability to focus on nearby objects, reducing its power of accommodation. This condition is known as presbyopia, and it is a common reason why older individuals often require reading glasses (convex lenses).
