When do we say that a particular person is suffering from hypermetropia? List two causes of this defect. Name the type of lens used to correct this defect.

Q: When do we say that a particular person is suffering from hypermetropia? List two causes of this defect. Name the type of lens used to correct this defect.

A person is said to be suffering from **hypermetropia** (or far-sightedness) when they can see distant objects clearly but cannot see nearby objects distinctly. ### Causes of Hypermetropia: 1. The focal length of the eye lens is too long. 2. The eyeball has become too small. ### Correction: This defect can be corrected by using a **convex lens** of appropriate power.

The Human Eye and the Colourful World

Hypermetropia

Official Answer

A person is said to be suffering from hypermetropia (or far-sightedness) when they can see distant objects clearly but cannot see nearby objects distinctly.

Causes of Hypermetropia:

The focal length of the eye lens is too long.
The eyeball has become too small.

Correction:

This defect can be corrected by using a convex lens of appropriate power.

HypermetropiaFar-sightednessFocal length too longEyeball too smallConvex lens

Marking Scheme

10.5 marks for defining Hypermetropia correctly.
21.0 mark for listing both causes (0.5 marks for each cause).
30.5 marks for naming the corrective lens (convex lens).

Hint

Hypermetropia is also known as far-sightedness. Think about what happens to the eyeball size and focal length to make the image form behind the retina, and what type of lens converges light.

Quick Oral Answer

Hypermetropia is far-sightedness. It is caused when the focal length of the eye lens is too long or the eyeball is too small. It is corrected using a convex lens.

Analysis & Explanation

In a normal eye, light rays from an object at $25\text{ cm}$ focus precisely on the retina. In a hypermetropic eye, the converging power of the eye's lens system is insufficient (either because the lens is too thin/focal length is too long, or the retina is too close to the lens due to a shortened eyeball). As a result, the light rays from a nearby object meet at a virtual point behind the retina, causing a blurred image. A convex lens converges the incoming rays slightly before they enter the eye, allowing the eye's lens to successfully focus them on the retina.

Common Mistakes

1Confusing the causes of hypermetropia with those of myopia (e.g., writing 'elongation of eyeball' instead of 'eyeball too small').
2Writing 'concave lens' instead of 'convex lens' for correction.

Interesting Facts

People with hypermetropia often have to hold reading materials much beyond $25\text{ cm}$ to see them clearly without straining their ciliary muscles.

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Frequently Asked Questions

How many marks does this question carry in CBSE Class 10 Science 2024?

This question carries 2 marks in the CBSE Class 10 Science 2024 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 "Hypermetropia" from CBSE Class 10 Science.

What type of question is this in the CBSE Class 10 Science 2024 paper?

This is a Very Short Answer question from Section B in the CBSE Class 10 Science 2024 paper.