What it shows
The eye lens forms an upside-down image on the retina, and the brain turns it upright. A water lens and screen show how focus works and why spectacles help.
The science
Light passes through the cornea and lens, and the lens focuses it on the retina, where the image is inverted. The brain flips it upright. The ciliary muscles change the thickness of the lens to focus on near or far objects. In myopia the image falls in front of the retina and a concave lens corrects it, and in hypermetropia it falls behind and a convex lens corrects it.
Materials
Cost: under Rs 50. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- A round clear plastic bottle or a plastic ball cut in half
- Water
- A small cardboard box painted black as the eyeball
- Butter paper as the retina
- A torch and a candle-shaped drawing
- Concave and convex lenses from an old pair of glasses (optional)
Safety
For this project: An adult must cut the bottle. Use the torch and do not use a real flame.
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.
All the safety rulesStep 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.
Fill the round bottle with water to make a lens.
Cut a hole in the front of the box and fit the bottle as a lens.
Fix butter paper at the back as the retina.
Place a bright picture in front and darken the room.
Move the box or the retina until a sharp image forms.
Observe the inverted image on the paper.
Move the picture closer and see that the image blurs and moves back.
Hold a convex spectacle lens in front to bring it into focus again and explain how it helps.
What you should see
A clear inverted image on the screen that blurs and refocuses when the distance or the extra lens changes.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
1Where is the image formed in the eye?
On the retina.
2Is the image upright or inverted?
Inverted on the retina, and the brain interprets it.
3Which lens corrects myopia?
A concave lens.
4What changes the shape of the eye lens?
The ciliary muscles.
Take it further
Measure the focal length of the bottle lens by focusing the image of a distant window.
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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