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Accommodation

Accommodation is the ability of the eye lens to change its curvature so that objects at different distances are seen clearly.

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Student-friendly explanation

When you look at a nearby object, the ciliary muscles contract and the lens becomes thicker, so its focal length decreases. When you look at a distant object, the ciliary muscles relax and the lens becomes thinner, so its focal length increases. This adjustment helps the eye form a sharp image on the retina without moving the eye itself.

How to write this in exams

  1. 1

    Start with the exact idea

    Accommodation is the ability of the eye lens to change its curvature so that objects at different distances are seen clearly.

  2. 2

    Then show how to use it

    1. Identify the object distance. 2. For near objects, the ciliary muscles contract and the lens becomes thicker. 3. For distant objects, the ciliary muscles relax and the lens becomes thinner. 4. The adjusted lens forms a sharp image on the retina. 5. State that this ability is called accommodation.

  3. 3

    Add one concrete example

    A student can read a notebook held close to the face and then quickly look at the classroom board across the room. The eye lens changes shape in both cases to keep the image clear.

  4. 4

    Avoid this incomplete answer

    A common wrong answer is that the eye moves to focus on objects. That is wrong because focusing is done by changing the lens shape, not by moving the eyeball.

Definition

Accommodation is the ability of the eye lens to change its curvature so that objects at different distances are seen clearly.

Example

A student can read a notebook held close to the face and then quickly look at the classroom board across the room. The eye lens changes shape in both cases to keep the image clear.

Rule to remember

The lens changes focal length by changing curvature; this is controlled by ciliary muscles.

Memory hook

Near object, thick lens; far object, thin lens.

Examples and method

Worked example

If a student shifts attention from a pencil 25 cm away to a wall 5 m away, the lens first becomes more convex for the pencil and then less convex for the wall. In both cases, the image is kept on the retina.

Method to apply

1. Identify the object distance. 2. For near objects, the ciliary muscles contract and the lens becomes thicker. 3. For distant objects, the ciliary muscles relax and the lens becomes thinner. 4. The adjusted lens forms a sharp image on the retina. 5. State that this ability is called accommodation.

Diagram support

Draw the eye with ciliary muscles, a thicker lens for near objects, and a thinner lens for distant objects. Label retina, cornea, iris, and lens.

How CBSE asks it

Explain how the eye adjusts its power to see objects at different distances. A ray diagram may also be asked with labels.

Avoid common mistakes

Common confusion

Many students think the eye moves forward and backward to focus. In reality, the eye lens changes shape while the eyeball stays in place.

Common wrong answer

A common wrong answer is that the eye moves to focus on objects. That is wrong because focusing is done by changing the lens shape, not by moving the eyeball.

Exam tip

In answers, mention ciliary muscles, lens curvature, and focal length change together. That combination earns full concept credit.

Quick check

Why can the same eye see both a book at close distance and a board at far distance clearly?

The eye can do this because of accommodation. The ciliary muscles change the shape of the lens, which changes its focal length so that images of both near and distant objects form clearly on the retina.

Answer writing and exam use

1-mark answer

Accommodation is the ability of the eye lens to change its curvature so that objects at different distances are seen clearly.

2-mark answer

Accommodation is the ability of the eye lens to change its curvature so that objects at different distances are seen clearly. The lens changes focal length by changing curvature; this is controlled by ciliary muscles. A student can read a notebook held close to the face and then quickly look at the classroom board across the room. The eye lens changes shape in both cases to keep the image clear.

3-mark answer

When you look at a nearby object, the ciliary muscles contract and the lens becomes thicker, so its focal length decreases. When you look at a distant object, the ciliary muscles relax and the lens becomes thinner, so its focal length increases. This adjustment helps the eye form a sharp image on the retina without moving the eye itself. The lens changes focal length by changing curvature; this is controlled by ciliary muscles. If a student shifts attention from a pencil 25 cm away to a wall 5 m away, the lens first becomes more convex for the pencil and then less convex for the wall. In both cases, the image is kept on the retina. Explain how the eye adjusts its power to see objects at different distances. A ray diagram may also be asked with labels. A common wrong answer is that the eye moves to focus on objects. That is wrong because focusing is done by changing the lens shape, not by moving the eyeball.
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