What it shows
Three mirrors set in a triangle reflect light again and again, turning a few coloured beads into a symmetrical pattern of many images. It shows how reflection works and how multiple reflections multiply images.
The science
A smooth surface reflects light at the same angle it arrives, so a shiny strip of plastic backed with black acts as a mirror. When two mirrors face each other at an angle, the image in one is reflected again in the other, making a ring of images; three mirrors in a triangle at 60 degrees give a pattern that repeats all round. The beads at the end are seen directly and also in every one of these reflections, so a small jumble of colour becomes a symmetrical star that changes every time the beads move.
Materials
Cost: free. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- An old CD case or a clear plastic sheet, cut into three strips, backed with black paper or black tape to make mirrors (free)
- A chips or cardboard tube
- Coloured beads or bits of coloured plastic
- A piece of clear plastic and a piece of butter paper for the end
- Tape, scissors and black paper
Safety
For this project: An adult must cut the plastic strips, which can have sharp edges, and check the edges are taped over. Use only beads and plastic pieces, never broken glass or bangle pieces, and keep small beads away from young children.
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.
Cut three strips of clear plastic from the CD case, each as long as the tube and about 3 cm wide, and tape over the edges.
Stick black paper or black tape on one side of each strip; the plain side now works as a mirror.
Tape the three strips together along their long edges into a triangle with the mirror sides facing inwards.
Slide the triangle into the tube and pack paper round it so it does not rattle.
Cut a small eyehole in the tube lid and fix it on one end.
At the other end, fix a clear plastic disc against the mirrors, drop in a few beads and plastic pieces, then close the end with a disc of butter paper so light comes in but the beads stay put.
Point the tube at a window, look through the eyehole and turn it slowly to watch the patterns change.
Try two mirrors instead of three, and four, and count how many repeated images you see each time.
What you should see
A working kaleidoscope that shows a six-pointed symmetrical pattern that changes as the beads tumble. Changing the number of mirrors changes the number of repeated images.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
01Why do you see so many beads when there are only a few?
Each mirror reflects the beads and also the reflections in the other mirrors, so the images multiply.
02What makes the clear plastic act as a mirror?
The black backing stops light passing through, so the smooth surface reflects it like a mirror.
03Why is butter paper used at the end?
It lets light in to light up the beads but hides the view outside so the pattern is clear.
04What happens with mirrors at a smaller angle?
More images appear, because the reflections are repeated more times round the circle.
Take it further
Replace the beads with a clear end and point the kaleidoscope at the world to make patterns from trees and buildings.
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.
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