Teacher sheet · Ages 10–11 · about 45–50 minutes
Light and colour: mirrors, rainbows and a blue sky
Lesson page: echoesof.science/school/light/ages-10-11/ · Pupil worksheet: echoesof.science/school/light/ages-10-11/print/
Learning aims
- Light travels in straight lines and reflects with equal angles.
- White light is a mixture of colours that can be split by refraction (dispersion).
- The colour of an object depends on which light it reflects and absorbs.
- Scattering explains the blue sky and red sunsets.
Lesson plan
| Time | Activity |
|---|---|
| 5 min | Show a mirror and a sheet of paper: both reflect light. What is different? |
| 10 min | Read the text. |
| 15 min | Make a rainbow in groups (on a sunny day, or with a strong torch). |
| 10 min | Light detective game together. |
| 5 min | Quiz. |
Materials for the experiment
- A clear glass of water
- A sunny window (or a strong torch)
- A sheet of white paper
- Optional: an old CD
Safety: Never look directly at the Sun. Keep the water away from electrical sockets.
Common misconceptions
| Pupils may think… | Actually… |
|---|---|
| Colour is paint inside the object. | An object's colour is the light it reflects; in red light, a 'green' leaf looks dark. |
| The sky is blue because it reflects the sea. | Air scatters blue light most; the sky is blue over deserts too. |
| White is not a colour of light. | White light is all colours mixed. |
Worksheet answers
- Ray in and ray out at equal angles to the normal (the line at right angles to the mirror).
- Red, orange, yellow, green, blue, (indigo,) violet.
- It reflects mainly yellow light and absorbs most of the other colours.
- At sunset sunlight crosses much more air, so most of the blue is scattered away and red and orange are left.
Quiz answers
- A ray hits a mirror at 30° to the normal. At what angle does it reflect? 30°. The angle of reflection equals the angle of incidence.[4]
- Why can you read a sheet of paper from any angle? Its rough surface scatters light in all directions. Rough surfaces give diffuse reflection.[4]
- Which colour bends most in a prism? Violet. Violet bends most, red least.[5]
- A leaf looks green because it… reflects mainly green light and absorbs most other colours. An object's colour is the light it reflects.[2]
- Why is the sky blue? Air scatters blue light more than red. Blue light, with shorter waves, is scattered most.[1]
- How long does sunlight take to reach Earth? About 8 minutes. It travels about 150 million km at about 300,000 km/s.[7]
Going further
Look at coloured objects through a red sweet wrapper or red cellophane. Which colours look black? Why?
Sources used in this lesson
- [1] Why Is the Sky Blue? (NASA Space Place): reliability High
- [2] Wave Behaviors (NASA Science (Tour of the Electromagnetic Spectrum)): reliability High
- [3] College Physics 2e, 25.1 The Ray Aspect of Light (OpenStax, Rice University): reliability High
- [4] College Physics 2e AP, 25.2 The Law of Reflection (OpenStax, Rice University): reliability High
- [5] College Physics 2e, 25.5 Dispersion: The Rainbow and Prisms (OpenStax, Rice University): reliability High
- [6] College Physics 2e, 24.3 The Electromagnetic Spectrum (OpenStax, Rice University): reliability High
- [7] Origin of Light (NASA Scientific Visualization Studio): reliability High
Full list with links and a note on each source's reliability: echoesof.science/school/light/sources/
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