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The human eye

边玩边学

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课程笔记

The Eye as an Optical Device

  • The human eye contains a convex lens that focuses light onto the retina.
  • A convex lens is wider in the middle than at the edges.
  • Rays of light refract by different amounts depending on where they hit the lens, causing them to converge at a focal point.
  • Convex lenses are used in glasses (for farsightedness), magnifying glasses, and telescopes.

Parts of the Eye and Their Functions

  • Cornea: Transparent layer at the front; some refraction occurs here.
  • Retina: Contains cells that detect light and colour; sensitive to bright light and can be damaged.
  • Lens: Refracts light; muscles change its shape to adjust focus for near or far objects.
  • Iris: Coloured part around the pupil; controls the amount of light entering the eye.
  • Pupil: Dark opening in the centre; light passes through it.
  • Nerve: Carries signals from the retina to the brain.

Pupil Size and Light Intensity

  • In bright light, the iris closes (constricts) to make the pupil smaller, protecting the retina from damage.
  • In dim light, the iris opens (dilates) to make the pupil larger, allowing more light to reach the retina.

Lens Shape and Refraction

  • The more curved the lens, the more light refracts.
  • A more curved lens has a shorter focal length (distance from lens to focal point).
  • Muscles change the lens shape to focus on objects at different distances.

Refraction of light entering the eye: light bends as it passes from air into the cornea/lens.

RefractionAirLensnormalincident30°refracted20°

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练习题

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  1. 1.A lens that is wider in the middle than at the edges is called a:

    Easy
    • Aconvex lens
    • Bconcave lens
    • Ccylindrical lens
    • Ddiverging lens
  2. 2.The human eye contains a:

    Easy
    • Aconvex lens
    • Bconcave lens
    • Cboth convex and concave lenses
    • Dno lens
  3. 3.Which part of the eye contains cells that detect light and colour?

    Easy
    • Aretina
    • Bcornea
    • Clens
    • Diris
  4. 4.The coloured part of the eye is the:

    Easy
    • Airis
    • Bpupil
    • Ccornea
    • Dretina
  5. 5.Which of the following is NOT a use of convex lenses?

    Easy
    • Aglasses for farsightedness
    • Bmagnifying glasses
    • Ctelescopes
    • Dglasses for nearsightedness
  6. 6.What happens to the pupil in very bright conditions?

    Easy
    • Ait becomes smaller
    • Bit becomes larger
    • Cit changes colour
    • Dit closes completely
  7. 7.The part of the eye that refracts light and can change shape is the:

    Easy
    • Alens
    • Bcornea
    • Cretina
    • Dpupil
  8. 8.A convex lens causes light rays to:

    Easy
    • Aconverge
    • Bdiverge
    • Creflect
    • Ddiffract

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