The rainbow
Raindrops act like tiny prisms.
After the rain
After a rain shower the air is full of tiny drops of water. The Sun shines.
What can sunlight do in these drops?
What this lesson covers
The idea
A rainbow is a natural spectrum formed by tiny water droplets acting as small prisms: they refract and disperse sunlight, reflect it internally and refract it again on leaving; it always forms opposite to the Sun.
After the rain
After a rain shower the air is full of tiny drops of water. The Sun shines.
What can sunlight do in these drops?
- Split into colours
- Turn into rain
- Stop completely
One drop
Press Next step to follow a ray through a water droplet.
Natural spectrum
A rainbow is a natural spectrum after a rain shower. The drops act like small prisms. They refract and disperse the sunlight, reflect it internally, and refract it again as it leaves the drop. Different colours reach the observer's eye. The rainbow forms opposite to the Sun.
A rainbow is a natural spectrum caused by dispersion of sunlight by tiny water droplets, which act like small prisms: they refract and disperse the light, reflect it internally, then refract it again. It forms opposite to the Sun.
Notes
A rainbow is formed by water droplets acting like small prisms: they disperse sunlight, reflect it internally and refract it again. It is always opposite to the Sun.
Check yourself
What does a rainbow need to form?
In which direction is a rainbow formed?
How many times does the ray reflect inside the droplet?
Answer: 1
Refract and disperse, reflect internally, then refract again.
Where can you also see a rainbow on a sunny day?
- Only clouds. A rainbow is caused by dispersion of sunlight by tiny water droplets in the atmosphere.
- Sunlight and tiny water droplets in the air — correct. Yes!
- A glass prism in the sky. The water droplets act like small prisms. No glass prism is needed.
- Towards the Sun. A rainbow is always formed in a direction opposite to that of the Sun.
- Straight overhead. A rainbow is always formed in a direction opposite to that of the Sun.
- Opposite to the Sun — correct. Yes!
- Through a waterfall or a fountain, with the Sun behind you — correct. Yes!
- Looking at the Sun through a window. You can see a rainbow when you look at the sky through a waterfall or a water fountain, with the Sun behind you.
- Looking at the Sun through a waterfall. The Sun should be behind you, because a rainbow is formed in a direction opposite to that of the Sun.