What it shows
Light travels in straight lines, so light from the top of an object goes to the bottom of the screen through a tiny hole. The image on the screen is upside down.
The science
Light travels in straight lines. Rays from the top of an object pass through the pinhole and go down to the bottom of the screen, while rays from the bottom go up. This crossing of rays inverts the image. A smaller hole gives a sharper but dimmer image. A real camera uses a lens in place of the hole to gather more light.
Materials
Cost: free. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- A cardboard tube such as a chips tube
- Black paper or black paint
- Butter paper or tracing paper
- A pin and aluminium foil
- Tape and scissors
- A bright object like a window or a candle behind glass (not near a flame)
Safety
For this project: An adult must cut the tube and use the pin. Never look at the Sun through the camera.
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.
Paint the inside of the tube black to stop reflections.
Cover one end with foil and make a tiny pinhole in the middle.
Cover the other end with butter paper as the screen.
Point the foil end at a bright window or tree and look at the screen in a dim room.
Observe the upside-down picture.
Make a hole twice as big and compare sharpness and brightness.
Slide a second tube over the first to change the length and see the image size change.
Draw the ray diagram that explains inversion.
What you should see
A dim, upside-down, reversed image of a scene appears on the screen.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
1Why is the image inverted?
Light rays cross at the pinhole.
2Why is a smaller hole sharper?
Fewer overlapping rays reach the screen.
3Why is the image dim?
Only a little light passes through the pinhole.
4What replaces the pinhole in a real camera?
A lens.
Take it further
Make the tube longer and measure how image height changes with distance.
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
Science projects
Physics Working Models Explained
Twenty classic models, how each works and how to make it
Science projects
Science Projects for Class 6 to 8
Working models matched to middle-school science topics