What it shows
The eye works like a camera. A lens at the front focuses light from the world onto a screen at the back, giving a small image that is upside down.
The science
Light from an object passes through the cornea and lens, which bend it so that rays meet to form a real, inverted image on the retina. The brain learns to turn the picture the right way up. The iris changes the size of the pupil, letting in more light in the dark and less in bright light. To focus on near things the ciliary muscles make the lens fatter, while in the model you focus by sliding the box.
Materials
Cost: under Rs 200. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- A shoebox or a tube box, painted black inside with black paper
- A magnifying glass or a spectacle lens of about 15 cm focal length
- A piece of tracing paper or butter paper for the retina
- A card with a round hole of about 1 cm for the pupil
- A cardboard sleeve or second box that slides over the first
- Tape and a black cloth
- A bright window scene or a torch pointed at a drawn object
Safety
For this project: An adult must cut the box. Never look at the Sun through the lens and never point it at the Sun, because it can burn paper and harm eyes.
Never use mains electricity: power models with cells, batteries or a low-voltage adapter. Sharp and hot tools, flames and lab chemicals need an adult or your teacher beside you. Keep magnets, button cells and small parts away from young children, and wash your hands after making.
Step by step
8 steps. Do them in order, and test each part before you go on to the next. Write what you notice in a notebook as you go.
Ask an adult to cut a round hole in one end of the box slightly smaller than the lens and a large window in the other end.
Fix the lens into the front hole with tape, with the card hole in front of it as the iris and pupil.
Tape tracing paper across the back window so it makes a screen that you can see from outside.
Make a sliding sleeve out of a second box so you can change the distance between lens and screen.
In a dim room face the lens towards a bright window and drape the black cloth over your head and the back of the box.
Slide the sleeve in and out until the window or a lit object appears sharp on the tracing paper.
Notice that the picture is upside down and small, then try a nearer object and refocus the box.
Make a pupil card with a smaller hole and see how the image gets dimmer but sharper.
What you should see
A clear, upside-down, left-right reversed image of the scene appears on the tracing paper. Nearer objects need the screen farther from the lens, and a smaller pupil hole makes the image dimmer.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
01Which part of the eye is the screen?
The retina.
02Is the image on the retina upright or inverted?
Inverted; the brain interprets it as upright.
03What does the iris do?
It changes the pupil size to control how much light enters the eye.
04How does the real eye focus on near objects?
The ciliary muscles make the lens thicker so it bends light more.
Take it further
Replace the lens with a thicker lens and measure how the focus distance changes, to explain short sight and long sight.
Change one thing, measure what happens, and add a table or chart of your readings: that is what turns a model into your own investigation.
Free ebooks for this project
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Biology Models Guide
Make the heart, lungs, kidney, eye, cell and more, and explain them well
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Your Science Exhibition Guide
Choose a project, build it, present it and answer the judges with confidence
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