What you need
This experiment works best near a bright window or outdoors in direct sunlight.
- A shallow bowl or tray
- Water
- A small mirror
- A white sheet of paper or card
- A towel for spills
What to do
Fill the bowl with water and place the mirror inside so that part of it is below the surface. Tilt the mirror until sunlight falls on it.
- Hold the white card where the reflected light lands
- Move the card slowly closer or farther away
- Adjust the mirror angle until a band of colours appears
- Notice the order and width of the colours
What is happening?
Sunlight looks white, but it contains many wavelengths of visible light. When the light moves through water, it changes direction. The mirror reflects it, and the colours spread apart because each wavelength bends by a slightly different amount.
This separation of colours is called dispersion. Raindrops create a rainbow through a related combination of refraction, reflection and dispersion.
Questions to explore
Try changing one part of the setup at a time and compare the result.
- What happens when the mirror angle changes?
- Does the rainbow become larger farther from the mirror?
- Which colours are easiest to see?
- Can you create the same effect with a glass prism?
Safety note
Do not look directly at the Sun or reflect bright light into anyone's eyes. Ask an adult to help with glass mirrors, and wipe up spilled water immediately.
