Consider the following reasons for the reddish appearance of the sun at the sunrise or the sunset: A. Light from the sun near the horizon passes through thinner layers of air. B. Light from the sun covers larger distance of the earth's atmosphere before reaching our eyes. C. Near the horizon, most of the blue light and shorter wavelengths are scattered away by the particles. D. Light from the sun near the horizon passes through thicker layers of air. The correct reasons are
Consider the following reasons for the reddish appearance of the sun at the sunrise or the sunset: A. Light from the sun near the horizon passes through thinner layers of air. B. Light from the sun covers larger distance of the earth's atmosphere before reaching our eyes. C. Near the horizon, most of the blue light and shorter wavelengths are scattered away by the particles. D. Light from the sun near the horizon passes through thicker layers of air. The correct reasons are
Options
The correct option is (d).
Explanation:
- According to the NCERT text, at old age, the crystalline lens of some people becomes milky and cloudy. This condition is known as cataract, which leads to a partial or complete loss of vision. A milky and cloudy lens is essentially an opaque eye lens.
- Option (a) (elongated eyeball) and Option (b) (excessive curvature of eye lens) are causes of myopia.
- Option (c) (weakened ciliary muscles) is a cause of presbyopia.
Marking Scheme
- 1Identifying that cataract makes the crystalline lens milky and cloudy (opaque) (1 mark)
Hint
Think about what happens to the crystalline lens of old people when it becomes 'milky and cloudy'.
Quick Oral Answer
A person suffering from cataract has a milky and cloudy crystalline lens, which becomes opaque and blocks light from reaching the retina. It is corrected by surgical removal of the cloudy lens and replacing it with an artificial lens.
Analysis & Explanation
Cataract is a medical condition common in older adults where the natural crystalline lens of the eye loses its transparency. The proteins in the lens clump together, making it milky, cloudy, and opaque. This prevents light from focusing properly on the retina, causing blurred vision or complete blindness. It can be corrected through cataract surgery where the opaque lens is replaced with an artificial intraocular lens.
Common Mistakes
- 1Confusing cataract with presbyopia, which is caused by the weakening of ciliary muscles.
- 2Associating cataract with changes in the shape of the eyeball.
Interesting Facts
Cataract surgery is one of the most common and safest surgical procedures performed worldwide, and it can fully restore vision by replacing the cloudy lens with a clear plastic one.
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Frequently Asked Questions
How many marks does this question carry in CBSE Class 10 Science 2020?
This question carries 1 mark in the CBSE Class 10 Science 2020 examination.
Which chapter does this question come from in Science?
This question is from the chapter "The Human Eye and the Colourful World" in the CBSE Class 10 Science syllabus.
What topic does this question cover in Science?
This question covers the topic "Defects of Vision and Their Correction" from CBSE Class 10 Science.
What type of question is this in the CBSE Class 10 Science 2020 paper?
This is a MCQ question from Section A in the CBSE Class 10 Science 2020 paper.