Make a rainbow

You will look for separated sunlight colours on white paper near a glass of water. Finding the right position takes patience because the coloured patch may be small or faint.

Science
Starter
About 15 minutes

Grown-up needed: yes for setup, nearby supervision and handling water or small items

What you need

A clear drinking glass of water handled by a grown-up
A sunny window
White paper
A tray

The rule

Sunlight only. No screens.

How to do it

Ask a grown-up to place the glass on the tray near the sunny window.
Set white paper behind or below the glass where light leaves it.
Let the grown-up move the paper slowly through the bright patch.
Look at the paper rather than towards the Sun.
Name the colours you can see in the separated patch.
Ask the grown-up to remove the glass from sunlight when finished.

Why it works

White sunlight contains a range of colours. When light crosses between air, glass and water, its direction can change. Different colours bend by slightly different amounts, so the outgoing light may spread into a coloured band. The curved glass affects where that band appears. A patch can contain overlapping colours or reflections as well, so not every bright spot is a clear rainbow. White paper makes a faint coloured band easier to notice.

Make it harder

Move the paper a little farther from the glass.
Compare paper positions without changing the water level.
Explain why the coloured band moves when the glass turns.

Ask Taz

Why does white sunlight contain different colours?
Why does water bend some colours more than others?
Why do I sometimes see only a bright patch?

Ask Taz

For grown-ups

A grown-up must handle the glass and avoid focusing sunlight on anything that could scorch. Nobody should look at the Sun or use magnifiers. The activity makes an optical effect visible without claiming every setup works immediately. Ask at dinner: “What did you move to make the colours easier to see?”

Taz is an AI and can be wrong, so stay close by. Read how safety works on Taz.

Show us yours

Film your hands and what you made, not your face or name. Ask a grown-up before posting anywhere else.

Questions parents ask

Can we use what we already have?

Start with the listed household materials. Keep the basic setup small and ask a grown-up to choose suitable items before beginning. The stated time is an estimate, so let the observation decide whether you need longer.

What should we record?

Note the prediction, the result and the one thing you changed. Keeping those separate helps a family discuss what happened without turning an activity into a competition.

Must the result be shared online?

No. A conversation at home is enough. If you choose to share, keep identifying details out and follow the grown-up permission line above.

More to try

See all Taz Challenges, or look through the science labs. One place for every why. Ask for early access at aitaz.com

Try it in 3D: Prism rainbow.