(a) A student suffering from myopia is not able to see distinctly the objects placed beyond 5 m. List two possible reasons due to which this defect of vision may have arisen. With the help of ray diagrams, explain (i) why the student is unable to see distinctly the objects placed beyond 5 m from his eyes. (ii) the type of the corrective lens used to restore proper vision and how this defect is corrected by the use of this lens. (b) If, in this case, the numerical value of the focal length of the corrective lens is 5 m, find the power of the lens as per the new Cartesian sign convention.
(a) A student suffering from myopia is not able to see distinctly the objects placed beyond 5 m. List two possible reasons due to which this defect of vision may have arisen. With the help of ray diagrams, explain (i) why the student is unable to see distinctly the objects placed beyond 5 m from his eyes. (ii) the type of the corrective lens used to restore proper vision and how this defect is corrected by the use of this lens. (b) If, in this case, the numerical value of the focal length of the corrective lens is 5 m, find the power of the lens as per the new Cartesian sign convention.
(a) Two possible reasons for a student suffering from myopia are: (i) excessive curvature of the eye lens, or (ii) elongation of the eyeball. (i) The student is unable to see distinctly the objects placed beyond 5 m from his eyes because in a myopic eye, the image of a distant object is formed in front of the retina and not at the retina itself. (ii) The defect is corrected by the use of a concave lens of suitable power. This lens will bring the image back on to the retina and thus the defect is corrected.
Marking Scheme
- 1Reasons for myopia (2 marks)
- 2Explanation of myopia with ray diagram (3 marks)
- 3Type of corrective lens and explanation of correction (3 marks)
- 4Power of the lens (2 marks)
Hint
Myopia is a defect of vision in which a person is unable to see distinctly the objects placed beyond a certain distance. The corrective lens used to restore proper vision is a concave lens of suitable power.
Quick Oral Answer
Myopia is a defect of vision in which a person is unable to see distinctly the objects placed beyond a certain distance. The corrective lens used to restore proper vision is a concave lens of suitable power.
Analysis & Explanation
Myopia is a defect of vision in which a person is unable to see distinctly the objects placed beyond a certain distance. This defect arises due to excessive curvature of the eye lens or elongation of the eyeball. The corrective lens used to restore proper vision is a concave lens of suitable power. This lens will bring the image back on to the retina and thus the defect is corrected.
Common Mistakes
- 1confusing myopia with hypermetropia
- 2incorrect ray diagram
Interesting Facts
myopia is a common defect of vision
concave lens is used to correct myopia
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Frequently Asked Questions
How many marks does this question carry in CBSE Class 10 Science 2017?
This question carries 5 marks in the CBSE Class 10 Science 2017 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.
Has this question appeared in other CBSE Science papers?
Yes, a similar question appeared in the 2017 CBSE Class 10 Science paper.
What type of question is this in the CBSE Class 10 Science 2017 paper?
This is a Long Answer question from Section A in the CBSE Class 10 Science 2017 paper.