Define the term power of accommodation of human eye. What happens to the image distance in the eye when we increase the distance of an object from the eye? Name and explain the role of the part of human eye responsible for it in this case.

Q: Define the term power of accommodation of human eye. What happens to the image distance in the eye when we increase the distance of an object from the eye? Name and explain the role of the part of human eye responsible for it in this case.

1. **Power of Accommodation:** The ability of the eye lens to adjust its focal length to clearly focus both distant and nearby objects on the retina is called the power of accommodation. 2. **Effect on Image Distance:** When we increase the distance of an object from the eye, the **image distance remains constant**. The image is always formed on the retina, which is at a fixed distance (approximately $2.3\text{ cm}$) from the eye lens. 3. **Part Responsible and its Role:** - The part of the eye responsible for adjusting the focal length is the **ciliary muscles**. - **Role in this case:** When the object distance increases (looking at a distant object), the ciliary muscles **relax**. This causes the eye lens to become **thin**, thereby **increasing its focal length**. This adjustment ensures that the parallel light rays coming from the distant object are focused precisely on the retina.

The Human Eye and the Colourful World

Power of Accommodation

Official Answer

Power of Accommodation: The ability of the eye lens to adjust its focal length to clearly focus both distant and nearby objects on the retina is called the power of accommodation.

Effect on Image Distance: When we increase the distance of an object from the eye, the image distance remains constant. The image is always formed on the retina, which is at a fixed distance (approximately $2.3\text{ cm}$ ) from the eye lens.

Part Responsible and its Role:

The part of the eye responsible for adjusting the focal length is the ciliary muscles.
Role in this case: When the object distance increases (looking at a distant object), the ciliary muscles relax. This causes the eye lens to become thin, thereby increasing its focal length. This adjustment ensures that the parallel light rays coming from the distant object are focused precisely on the retina.

power of accommodationadjust focal lengthimage distance remains constantretinaciliary musclesrelaxlens becomes thinfocal length increases

Marking Scheme

1Definition of power of accommodation (ability of eye lens to adjust focal length) (1 mark)
2Stating that the image distance remains constant/unchanged (1 mark)
3Naming ciliary muscles and explaining that they relax to make the lens thin and increase focal length (1 mark)

Hint

Think about where the image must always be formed for us to see clearly, and how ciliary muscles change the shape of the lens when relaxing.

Quick Oral Answer

The power of accommodation is the eye's ability to change its focal length. When an object is moved further away, the image distance remains constant because the ciliary muscles relax, making the lens thinner to increase its focal length and keep the image focused on the retina.

Analysis & Explanation

The human eye is a remarkable optical instrument. Unlike a photographic camera where the lens is moved back and forth to focus objects at different distances (changing the image distance), the human eye has a fixed image distance (the distance between the lens and the retina). To focus objects at varying distances, the eye changes the focal length of its crystalline lens. This is achieved through the action of ciliary muscles. When looking at distant objects, the ciliary muscles relax, making the lens thin and increasing its focal length. When looking at nearby objects, the ciliary muscles contract, making the lens thick and decreasing its focal length.

Common Mistakes

1Writing that the image distance increases or decreases. Remember, the eyeball size does not change, so image distance is always constant.
2Stating that ciliary muscles contract when looking at distant objects. They actually relax.

Interesting Facts

The human eye lens is made of a fibrous, jelly-like material, allowing it to easily change shape, unlike glass or plastic lenses which have a rigid focal length.

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Frequently Asked Questions

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

This question carries 3 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 "Power of Accommodation" from CBSE Class 10 Science.

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

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