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3.6.4Stoichiometry

Structure of the Eye — Cambridge IGCSE Chemistry 0620 Revision Notes & Topical Questions

5 min read 4 parts Lesson 15 of 28 Unit quiz

📚 Cambridge IGCSE Chemistry 0620 Hub / Topical Revision
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Curriculum Equation Key قوانين المول والحسابات الكيميائية - Moles & Stoichiometry FormulasFast Exam Solution
n = m / M_r | N = n × N_A (6.022 × 10²³) | M = n / V | V_gas = n × 22.4 L (STP)
Word Equation & Conditions: عدد المولات = الكتلة بالجرام ÷ الكتلة المولية | عدد الجسيمات = عدد المولات × عدد أفوجادرو
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Part 1 of 4Refracting Parts

Light is refracted at two places in the eye before it reaches the retina.

Cornea
  • Cornea A transparent layer covering the front of the eye that protects it and refracts most of the light entering the eye.
Lens
  • Lens A transparent structure behind the iris that refracts light further and changes shape to fine-tune the focus.
Ciliary muscles
  • Ciliary muscles Muscles that change the tension in the suspensory ligaments, which alters the shape and thickness of the lens.
Suspensory ligaments
  • Suspensory ligaments Fibres joining the ciliary muscles to the lens, which pull and stretch the lens as the muscles change.

Part 2 of 4Path of Light Through the Eye

1
Light enters the eye through the cornea, which refracts the rays inwards towards the centre of the eye.
2
The light passes through the pupil, an opening whose size is set by the surrounding iris.
3
The lens refracts the rays again so that they converge onto the retina at the back of the eye.
4
The image formed on the retina is real, inverted and diminished, and the brain interprets it so that it appears the correct way up.
PartMain function
CorneaProtects the eye and refracts light
LensFine focusing by changing shape
IrisControls the size of the pupil
RetinaDetects the image using light-sensitive cells

Part 3 of 4Iris, Pupil and Retina

Iris, Pupil and Retina
Iris
  • Iris A ring of muscles around the pupil that controls how much light enters the eye by changing the size of the pupil.
Pupil
  • Pupil The opening through which light enters; it widens in dim light and narrows in bright light.
Retina
  • Retina A layer of light-sensitive cells lining the back of the eye, which detects the image and sends signals to the brain.
Image orientation
  • Image orientation The image on the retina is inverted, because rays from the top of the object strike the bottom of the retina.

Part 4 of 4Exam Checklist & Tips

3.6.4 – Key Points for the Exam

  • Cornea The transparent outer layer of the eye that refracts light and protects the eye.
  • Lens A transparent structure that refracts light and changes shape to focus the image.
  • Iris A ring of muscle that controls the size of the pupil.
  • Pupil The hole in the centre of the iris through which light enters the eye.
  • Retina The light-sensitive layer at the back of the eye that detects the image.
  • Ciliary muscles Muscles that control the shape of the lens.

Common Mistakes

  • Saying the lens does most of the refracting; most of the refraction happens at the cornea.
  • Stating that the image on the retina is upright; it is inverted and the brain corrects it.
  • Saying the pupil itself contracts; the iris changes the size of the pupil.
  • Confusing the ciliary muscles with the iris, which controls the amount of light entering.

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