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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.

In one line: Near object, thick lens; far object, thin lens.

Practice This Concept

Understand it

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.

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.

Formula and rule

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

See it worked out

Follow the example line by line, then use the same method on new questions.

Worked example

1If 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.
2In both cases, the image is kept on the retina.

Method you can reuse

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

Sketch it in your answer

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.

Check yourself

Answer the question in your head before opening the answer.

Try it yourself

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

Think first, then show answer

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.

Common wrong answer

The eye moves to focus on objects.

Why it loses marks: Focusing is done by changing the lens shape, not by moving the eyeball.

Don't mix this up

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

Exam tip

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

Write it in the exam

Each point is worth about one mark. Write point 1 for a 1-mark question and keep adding points as the marks go up.

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.

1
Enough for 1 mark
Accommodation is the ability of the eye lens to change its curvature so that objects at different distances are seen clearly.
2
Add for 2 marks
This adjustment helps the eye form a sharp image on the retina without moving the eye itself.
3
Add for 3 marks
In both cases, the image is kept on the retina.

MCQ Quiz

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