Define the term power of accommodation of human eye. Write the name of the part of eye which plays a major role in the process of accommodation and explain what happens when human eye focuses (i) nearby objects and (ii) distant objects.
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Model Answer
Power of Accommodation: The ability of the eye lens to adjust its focal length to clearly see objects at different distances is called the power of accommodation.
Part responsible: The ciliary muscles play a major role in accommodation.
(i) Nearby objects: When focusing on nearby objects, the ciliary muscles contract, increasing the curvature of the eye lens. The lens becomes thicker, decreasing its focal length, thus forming a clear image on the retina.
(ii) Distant objects: When focusing on distant objects, the ciliary muscles relax, decreasing the curvature of the eye lens. The lens becomes thinner, increasing its focal length, thus forming a clear image on the retina.
Source: Chapter 10, Section 10.1.1 – Power of Accommodation
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Explanation
- Definition (1 mark): Must include "adjust focal length" and "different distances."
- Part named (½ mark): Ciliary muscles — not cornea, iris, or retina.
- Nearby & distant (1½ marks): Examiners look for the paired contrasts — contract/relax, thicker/thinner, focal length decreases/increases. All four terms should appear. Missing any pair costs marks.
- Keep sentences crisp; avoid repeating the definition when explaining each case.