7.11Chapter 7: Light

The eye and the camera — Alhussan Physics - Stage 8 Revision Notes & Topical Questions

5 min read 8 parts Lesson 11 of 12 2 quizzes

📚 Alhussan Physics - Stage 8 Hub / Topical Revision

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Lesson summary

Physics 7.11 The eye and the camera — Retina, Cornea, Lens and Focusing — Alhussan International Academy — Physics (Stages 7–9) notes: Describe how the eye and a camera work and compare them.PartFunctionCorneaTransparent outer layer that helps focus lightPupilThe hole where light…

Light path
Inverted image
Three types of cone
Colour blindness
Distant objects
Near objects

Part 1 of 6Parts of the eye

Part	Function
Cornea	Transparent outer layer that helps focus light
Pupil	The hole where light goes in
Iris	Coloured muscle that controls the size of the pupil
Lens	Jelly-like structure that focuses light onto the retina with the cornea
Retina	Where the image forms; contains light-sensitive cells
Optic nerve	Carries the signal from the retina to the brain

Eyeball
- It is filled with a liquid that keeps it nearly spherical.

Part 2 of 6Forming an image

Light path

Light reflected from an object enters through the cornea, pupil and lens and is focused on the retina.

Inverted image

The image on the retina is upside down, and the brain makes it the right way up.

Signals

Light-sensitive cells in the retina produce signals that are sent to the brain.

Part 3 of 6Rods and cones

Rods and cones

Rods

They are mainly around the edge of the retina and are sensitive to dim light.

Cones

They are mainly in the centre of the retina and are sensitive to bright light and colour.

Three types of cone

Each is very sensitive to red, green or blue light, which is why these are the primary colours of light.

Colour

The cones absorb light and send signals to the brain, which produces the coloured image.

Colour blindness

About 1 in 20 people, usually men, have cones that do not work properly and find red and green hard to tell apart.

Part 4 of 6Focusing near and far objects

Distant objects

The light is nearly parallel; the lens muscles relax and the lens becomes thinner.

Near objects

The light is spreading out; the ciliary muscles contract and the lens becomes thicker and more curved.

Iris

In bright light the pupil becomes smaller, and in dim light it becomes larger.

Part 5 of 6How a camera works

Light and image

Light reflected from the object enters through the aperture and the lens focuses an inverted image at the back.

Film

Cameras in the past captured the image on photographic film.

Sensors

Modern cameras, including phone cameras, use electronic sensors so the image can be stored or transferred easily.

Part 6 of 6Comparing the eye and the camera

Eye	Camera
Cornea and lens focus light	Lens focuses light
Iris controls pupil size	Aperture controls light entering
Retina detects the image	Film or sensor detects the image
Lens changes shape to focus	Lens moves to focus
Image is inverted	Image is inverted

Key terms

Term	Meaning
Cornea	The transparent outer layer of the eye that helps focus light.
Retina	The layer at the back of the eye containing light-sensitive cells.
Iris	The muscle that controls the size of the pupil.
Rods	Retina cells sensitive to dim light.
Cones	Retina cells sensitive to bright light and colour.
Aperture	The hole that lets light into a camera.