Daily Read / Everyday Physics
Everyday Physics · Integrate text and diagram evidence to explain a process
How Does a Rainbow Form?
Follow sunlight through a raindrop and combine prose with a process diagram to explain refraction, internal reflection, colour separation and why the Sun must be behind the observer.
Device/browser voice. Pronunciation and availability vary.
A rainbow is a light path, not a coloured object hanging in one place
A rainbow appears when sunlight, water droplets and an observer line up in the right geometry. NOAA explains that the Sun is behind the observer while water droplets are in front. The rainbow is an optical phenomenon created by light reaching the observer from many droplets.
That means two people standing in different places do not receive exactly the same rays from exactly the same droplets. The useful reading question is not 'where is the rainbow stored?' but 'what path does the light follow to the eye?'[1]
Step 1: sunlight enters a droplet and bends
When sunlight passes from air into liquid water, its direction changes. This bending is called refraction. NOAA describes the light as slowing and bending as it enters the denser water.
The first bend matters because the incoming white sunlight is already beginning to separate by wavelength. A process diagram should therefore show the ray changing direction at the front surface of the droplet.[1]
Step 2: some light reflects inside the droplet
After entering the droplet, some of the light reaches the back surface and reflects. The National Weather Service describes this as an internal reflection that redirects the light back toward the front of the droplet.
Reflection is different from refraction. Reflection changes the ray by bouncing it from a surface; refraction changes direction as light crosses between materials. A diagram that labels both processes helps prevent those words from being swapped.[2]
Step 3: the light leaves, bends again and reaches the observer
The returning light crosses from water back into air and refracts again. The ray that finally reaches the observer has therefore gone through a sequence: refraction in, internal reflection, refraction out.
A strong explanation needs the full chain. Saying only 'water acts like a prism' leaves out the internal reflection and the observer geometry that send the separated light back toward the eye.[1]
Why the colours separate
Sunlight contains many visible wavelengths. NOAA notes that different wavelengths bend by slightly different amounts. Red light bends less than violet light, so the outgoing rays are separated by colour.
The primary rainbow therefore shows red toward the outside or top of the arc and violet toward the inside or bottom. The colour order is evidence that the wavelengths did not all follow exactly the same path through the droplet.[1]
Use the diagram as evidence, not decoration
A process diagram can show information that is easy to lose in a paragraph: which side the sunlight enters, where the internal reflection occurs, and which direction the outgoing coloured rays travel toward the observer.
To integrate sources, point to one feature in the diagram and connect it to one sentence in the text. For example: the arrow bends at the air-water boundary, matching the text's definition of refraction. Then explain what that step contributes to the whole process.[2]
Fast lesson
Use these checks before you answer the practice questions.
Follow where the light enters, turns and exits before naming each process.
State what the diagram shows, then cite the sentence that explains why it happens.
Refraction and reflection are steps; the visible colour arc is the result seen by the observer.
Common mistakes
Why this fails: The ray refracts when it crosses air-water boundaries and reflects at an internal surface.
Why this fails: Each source contributes different information about order, position and meaning.
Why this fails: The visible effect depends on the observer, Sun and droplets lining up.
Word Lab
Use the meaning, hear the word, then try it in your own sentence.
refraction
nounthe bending of light when it passes from one material into another
Refraction changes the direction of sunlight as it enters a raindrop.
reflection
nounthe bouncing of light from a surface
Internal reflection turns part of the light back inside the droplet.
wavelength
nounthe distance between repeating points of a wave; different visible wavelengths are perceived as different colours
Different wavelengths bend by slightly different amounts.
spectrum
nouna range of wavelengths or colours arranged in order
A rainbow spreads visible light into a spectrum.
droplet
nouna very small drop of liquid
Sunlight can be refracted and reflected by a water droplet.
observer
nouna person who watches or measures something
The observer sees the rainbow with the Sun behind them.
sequence
nouna set of steps or events in a particular order
The diagram shows the sequence of the light path.
integrate
verbto combine information from more than one source into one explanation
Integrate the paragraph and diagram before writing your answer.
Check your understanding
Choose an answer, explain your choice, and then check. Hints and retries are welcome.
Try the questions here. Public practice does not save a learning record.
Foundation
Foundation practice
Identify steps and read the diagram literally.
1. What is the first labelled process when sunlight enters the droplet?
2. What happens after the first refraction in the simplified primary-rainbow path?
3. What happens as the light leaves the droplet?
4. Which arrow should point toward the observer: incoming sunlight or outgoing separated light?
5. What does droplet mean?
6. What does observer mean?
Core
Core practice
Connect diagram features to the explanation.
7. The diagram bends the ray at the front edge of the droplet. Which sentence idea explains that bend?
8. The diagram shows a bounce at the back of the droplet. What process is that?
9. Why are the outgoing coloured rays drawn slightly apart?
10. Why are the droplets in front of the observer in the model?
11. Complete the chain: white sunlight → refraction → ______ → refraction out → separated colours.
12. What information is easier to see in a diagram than in a paragraph?
Reasoning
Reasoning practice
Use the two sources together rather than repeating labels.
13. A student says the ray goes straight through the droplet. What diagram evidence contradicts that?
14. A student says reflection happens before the light enters the water. What corrects the claim?
15. Can one ray experience both refraction and reflection?
16. Why does red appear on a different part of the arc from violet?
17. Does the single-droplet diagram show every droplet that contributes to a real rainbow?
18. What should you do first when a diagram and paragraph seem to disagree?
Challenge
Challenge practice
Build a complete explanation from spatial and textual evidence.
19. Write the shortest complete primary-rainbow process chain.
20. Why can two observers in different places see different rainbow geometry?
21. If an outgoing arrow were drawn toward the Sun instead of toward the observer, what would be wrong?
22. What observation supports the claim that visible wavelengths follow slightly different paths?
23. Why is naming three processes not enough without order?
24. Give one sentence that explicitly uses both sources.
Practice answer key
- 1. Refraction.
Crossing from air into water bends the ray. - 2. The light reflects inside the droplet.
The ray reaches the back of the droplet and is redirected. - 3. It refracts again.
The ray crosses from water back into air. - 4. The outgoing separated light.
The observer sees light after it has travelled through the droplet. - 5. A very small drop of liquid.
The lesson uses water droplets as the optical material. - 6. A person who watches or measures something.
The rainbow's appearance depends on the observer's viewpoint. - 7. Light refracts when it passes from air into water.
The diagram feature and prose definition describe the same boundary event. - 8. Internal reflection.
The light remains inside the droplet while changing direction. - 9. Different wavelengths refract by slightly different amounts.
The separation represents dispersion of visible colours. - 10. They must send the redirected light back toward the observer's eyes.
The geometry places the rainbow opposite the Sun. - 11. internal reflection
That is the middle step in the primary-rainbow path. - 12. The direction and order of the light path.
Arrows make spatial sequence visible. - 13. The arrows change direction at the boundary and inside the droplet.
Those bends and the bounce show the path is not straight. - 14. The first step shown and described is refraction into the water.
The internal reflection occurs only after entry. - 15. Yes.
The rainbow path includes both processes in sequence. - 16. Their wavelengths bend by different amounts.
Different refraction angles separate the colours. - 17. No.
It is a simplified model of the light path through one droplet. - 18. Check labels, arrow direction and exactly which step each source describes.
Apparent conflict can come from comparing different parts of a process. - 19. Sunlight refracts into a droplet, reflects inside, refracts out, separates by wavelength and reaches the observer.
The chain includes the required optical steps and the result. - 20. Each receives light along a different set of Sun-droplet-observer paths.
A rainbow depends on viewpoint, not one fixed coloured object. - 21. It would not represent the light that reaches the observer to form the visible rainbow.
The primary diagram must route the outgoing ray to the viewer. - 22. The colours appear separated in a consistent order.
A single identical path would not create distinct colour bands. - 23. A process explanation must show how one step leads to the next.
Sequence is causal information, not just vocabulary. - 24. The diagram's inward bend matches the text's refraction description, and the internal bounce shown next explains how the ray turns back toward the observer.
The sentence links a visual feature with prose meaning and process role.
Related skills
Put it in your own words
This draft is not saved when you leave or refresh the page.
Check your own explanation
This is self-review, not automatic marking.
Compare with a model response
The diagram shows sunlight entering the front of a water droplet and bending, which matches the passage's definition of refraction. The ray then bounces from the inside back surface, an internal reflection. As it leaves the droplet it refracts again, and the outgoing coloured arrows separate because different wavelengths bend by slightly different amounts. Those arrows point toward the observer, who has the Sun behind them.
Sources and revision notes
Source check: 2026-09-30. Grade guidance is an editorial suggestion, not a standardised reading score.
What changed in this edition?
Initial release. Refraction, internal reflection, wavelength-dependent colour separation, observer geometry and primary-rainbow colour order were checked against NOAA NESDIS and the National Weather Service on 2026-09-30.