Page 236 - Physics_Form_2

Physics for Secondary Schools

Lens
Sclera

Aqueous humour
Retina

Cornea
Optic nerve
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Pupil

Iris

Suspensory ligaments
Ciliary muscle Vitreous humour

Figure 6.18: Parts of a human eye

Images formed by the human retina turn the light into electrical signals, which
eye travel to the brain through the optic nerve.
When light strikes the eye, it
passes through the cornea. The The indices of refraction of both the aqueous humour
cornea is shaped like a dome, and the vitreous humour are about 1.336, which is
so it bends the light to help the nearly equal to that of water. The crystalline lens,
eye focus. The light through while not homogeneous, has an average index of
the cornea and the aqueous refraction of 1.437. This is not very different from
humour enters the eye through the indices of the aqueous and vitreous humour.
the pupil. The iris controls the As a result, most of the refraction of light entering
size of the pupil, which in turn the eye occurs at the outer surface of the cornea, as
determines the amount of light shown in Figure 6.19.
that enters the eye. Next, light
passes through the lens. The
lens works together with the
cornea to focus light correctly
on the retina. Light from
the lens travels through the
vitreous humor towards the
retina. The image is formed
on the retina as illustrated in
Figure 6.19. When light hits
the retina to form the image,
the photoreceptors on the Figure 6.19: Image formation by the human eye

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Student’s Book Form Two

Physics Form 2 Final.indd 230 25/10/2025 10:28