Accommodation: near and distant objects
הוצג| English | משמעות |
|---|---|
| accommodation/əˌkɒməˈdeɪʃn/ | הסתגלות עין |
| suspensory ligament/səˈspensəri ˈlɪɡəmənt/ | רצועת תלייה |
What would explain this observation?
- A close object and a distant object need different lens shapes to form a focused image on the same retina. Trace muscle, ligament and lens changes in order.
Build the model
- Accommodation 视觉调节 is changing the lens shape to focus on objects at different distances.
- For a near object, ciliary muscles contract, suspensory ligaments 悬韧带 loosen and the lens becomes thicker, refracting light more strongly.
- For a distant object, ciliary muscles relax, the ligaments are pulled tight and the lens is pulled thin, refracting light less strongly.
- accommodation: Changing lens shape to focus on near or distant objects.
- suspensory ligament: A connection transmitting tension that affects the lens shape.
Which set of changes focuses on a near object?
רמת קושי 1/5 · 100 מטבעות + בונוס קטן בהשלמה הראשונה היום
For a near object the ciliary muscles contract, the suspensory ligaments go slack, and the elastic lens rounds up thicker, adding refractive power. The reverse set thins the lens for distant objects.
Match each technical term to its precise meaning.
רמת קושי 2/5 · 140 מטבעות + בונוס קטן בהשלמה הראשונה היום
Use the definitions to distinguish related quantities and processes.
Choose evidence that can test it
- The lens does not actively pull itself into shape like a muscle.
- Explain the mechanical connection: ciliary-muscle action changes tension in the suspensory ligaments, allowing or pulling the elastic lens into the appropriate shape.
- A change in pupil size alone does not supply the required accommodation explanation.
In the lab: Use a labelled paper or elastic-lens model under teacher supervision. Compare near and far configurations and annotate the three linked changes. Interpret ray diagrams by checking that rays focus on the retina. A diagram should clearly distinguish focusing from the separate bright/dim pupil response; do not apply pressure or chemicals to a real eye.
Which two habits make the investigation or model in this case more defensible?
רמת קושי 2/5 · 140 מטבעות + בונוס קטן בהשלמה הראשונה היום
Stating the conditions and assumptions lets others repeat the work exactly, and recording the supporting evidence lets them check the conclusion. Hiding disagreeing results removes the evidence that could challenge a wrong conclusion, and one measurement can never establish a wider claim.
Work from known quantities
- Known: a supplied drawing magnifies a model lens dimension tenfold.
- A 25 mm drawn thickness represents 2.5 mm in the stated model; a 15 mm drawing represents 1.5 mm.
- The geometrical comparison shows which model is thicker but does not give a real person’s lens dimensions or calculate focusing power.
Your turn: A model lens thickness is drawn as 28 mm at magnification 8. Calculate the represented thickness.
A model lens thickness is drawn as 28 mm at magnification 8. Calculate the represented thickness.
רמת קושי 2/5 · 140 מטבעות + בונוס קטן בהשלמה הראשונה היום
The result is 3.5 mm. Known: drawn thickness 28 mm at magnification 8. Use real size = drawn size / magnification. Thickness = 28/8 = 3.5 mm in the stated model. The drawing says nothing about any real eye.
Check the conclusion and its limits
- Near focusing uses contracted ciliary muscles and loose ligaments, not the reverse.
- For distance, tightening the ligaments pulls the lens thin.
- Drawing thickness and actual thickness need a stated scale.
- This section does not require a clinical eye test or a spectacle prescription.
Not true: For near focus the suspensory ligaments become tighter and pull the lens thinner. Near focus needs a THICKER lens. Tight ligaments pull the lens thin, which suits distant objects; for near objects the ciliary muscles contract so the ligaments loosen and the lens springs thicker.
- Accommodation is changing the lens shape to focus on objects at different distances.
- The lens does not actively pull itself into shape like a muscle.
- Watch for: near focusing uses contracted ciliary muscles and loose ligaments, not the reverse.
Near focus needs a THICKER lens.
רמת קושי 1/5 · 100 מטבעות + בונוס קטן בהשלמה הראשונה היום
True. Near focus needs a THICKER lens. Tight ligaments pull the lens thin, which suits distant objects; for near objects the ciliary muscles contract so the ligaments loosen and the lens springs thicker.
Changing lens shape to focus on near or distant objects: write the technical term.
רמת קושי 1/5 · 100 מטבעות + בונוס קטן בהשלמה הראשונה היום
accommodation means Changing lens shape to focus on near or distant objects.