What eye defect is hypermetropia? Describe with a ray diagram how this defect of vision can be corrected by using an appropriate lens.
What eye defect is hypermetropia? Describe with a ray diagram how this defect of vision can be corrected by using an appropriate lens.
Hypermetropia (Far-sightedness):
Hypermetropia is a refractive defect of vision in which a person can see distant objects clearly but cannot see nearby objects distinctly. The near point of a hypermetropic eye is farther away from the normal near point ().
Causes of Hypermetropia:
- The focal length of the eye lens is too long.
- The eyeball has become too small.
Correction:
This defect is corrected by using a convex lens of appropriate power. The converging convex lens provides the additional focusing power required to converge the light rays from a nearby object so that they focus exactly on the retina.
Correction Ray Diagram:
Marking Scheme
- 1Definition of Hypermetropia and its two main causes (1 mark)
- 2Explanation of how a convex lens corrects the defect (1 mark)
- 3Correctly drawn and labeled ray diagram showing correction with a convex lens focusing rays on the retina (1 mark)
Hint
Hypermetropia is far-sightedness. Think about which lens is a converging lens to help focus light rays that are currently focusing too far behind the retina.
Quick Oral Answer
Hypermetropia is far-sightedness, where a person cannot see nearby objects clearly because the image forms behind the retina. It is corrected using a convex lens of appropriate power.
Analysis & Explanation
In a hypermetropic eye, light rays coming from a nearby object (placed at the normal near point of ) are focused at a point behind the retina because the eye's lens system lacks sufficient converging power. To correct this, a convex lens is placed in front of the eye. This lens pre-converges the incoming rays so that they appear to diverge from the defected eye's actual near point (). The eye lens then easily focuses these rays directly onto the retina, restoring clear near vision.
Common Mistakes
- 1Drawing a concave lens instead of a convex lens for correction.
- 2Showing the corrected rays still focusing behind the retina.
- 3Confusing the causes of hypermetropia with those of myopia (e.g., writing 'elongation of the eyeball' instead of 'eyeball has become too small').
Interesting Facts
As people age, they often develop a similar near-vision defect called presbyopia due to the gradual weakening of ciliary muscles and loss of flexibility of the eye lens, which also requires convex lenses for correction.
Spotted a mistake or something unclear?
Tell us — we fix reported answers fast.
Frequently Asked Questions
How many marks does this question carry in CBSE Class 10 Science 2011?
This question carries 3 marks in the CBSE Class 10 Science 2011 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 2011 paper?
This is a Short Answer question from Section A in the CBSE Class 10 Science 2011 paper.