How does the focal length of eye lens change as the distance of the object from the eyes is altered ? Explain.
Generated by claude-sonnet-4-6 · 2026-06-15 06:51 · grounding rag
Model Answer
When an object is far away, the ciliary muscles are relaxed, making the eye lens thin. Its focal length increases, enabling clear vision of distant objects.
When an object is close to the eye, the ciliary muscles contract, increasing the curvature of the lens, making it thicker. Its focal length decreases, enabling clear vision of nearby objects.
This ability of the eye lens to adjust its focal length is called accommodation.
Source: Chapter 10, Section 10.1.1 — Power of Accommodation
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Explanation
- Examiners expect two clear cases: distant object → relaxed muscles → thin lens → increased focal length; near object → contracted muscles → thick lens → decreased focal length.
- Always use the keyword accommodation — it fetches a mark.
- Keep it to 2–3 sentences covering both cases; no diagrams needed for 2 marks unless asked.