Activity 01
Prism Rainbows
In a darkened room, students use a ray box and a glass prism to split a beam of white light into the visible spectrum. They can project the spectrum onto a white card and label the colours in the correct order.
Explain how a prism separates white light into the colours of the spectrum.
Facilitation TipEnsure the slit in the ray box is narrow to produce a clear and well-defined spectrum.
What to look forUse mini-whiteboards for students to draw a diagram showing what happens when white light hits a green leaf, labelling the reflected and absorbed colours.
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Activity 02
Colour Filter Investigation
Students observe various coloured objects through red, green, and blue filters (e.g., cellophane). They record the apparent colour of each object and explain their observations based on which colours of light are transmitted by the filter and reflected by the object.
Analyse why a red object appears red in white light and black in blue light.
Facilitation TipEncourage students to predict the outcome for each object and filter combination before they test it.
What to look forA short, structured quiz at the end of the topic featuring questions that require students to apply their knowledge, for example, 'Explain why a red snooker ball appears black under a blue light'.
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Activity 03
Additive Light Mixing
Using three torches or ray boxes with red, green, and blue filters, students overlap the beams of light on a white screen. They can identify the secondary colours produced (cyan, magenta, yellow) and the effect of mixing all three.
Compare the additive mixing of coloured lights with the subtractive mixing of coloured pigments.
Facilitation TipThis works best as a teacher-led demonstration in a very dark room to ensure the colours are vivid.
What to look forStudents work in pairs to create a concept map linking key vocabulary like 'dispersion', 'reflection', 'pigment', and 'spectrum', then review each other's maps for accuracy and completeness.
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Activity 04
Subtractive Paint Mixing
Students are given primary paint colours (cyan, magenta, yellow) and mix them on a palette or white tile. They discover how these pigments combine to create secondary colours and a dark colour when all are mixed, demonstrating subtractive mixing.
Explain how a prism separates white light into the colours of the spectrum.
Facilitation TipRemind students to use small amounts of paint and to clean their brushes between colours to avoid contamination.
What to look forUse mini-whiteboards for students to draw a diagram showing what happens when white light hits a green leaf, labelling the reflected and absorbed colours.
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Generate Complete Lesson→A few notes on teaching this unit
Start with the 'wow' factor of a prism dispersing light to immediately engage students. Use clear, practical demonstrations to distinguish between additive light mixing (torches) and subtractive pigment mixing (paints). Consistently use the language of 'reflection' and 'absorption' to reinforce the core mechanism of how we perceive colour.
Following these activities, students will be able to explain not only how a rainbow is formed but also why a t-shirt looks a certain colour and how the screen they are looking at works.
Watch Out for These Misconceptions
Colour is a physical property of an object, like its mass or texture.
An object's colour depends on the light it reflects. A red apple appears red because its surface reflects red wavelengths of light and absorbs all other colours. In the absence of red light, it cannot reflect red and will appear black.
Mixing coloured paints and mixing coloured lights follow the same rules.
Mixing light is additive: adding colours makes things brighter, with red, green and blue light combining to make white. Mixing paint is subtractive: pigments absorb light, so adding colours makes things darker, with cyan, magenta and yellow combining to make a dark brown or black.
White is the absence of colour, and black is a colour.
White light is a mixture of all the colours of the visible spectrum. Black is the absence of visible light; an object appears black when it absorbs all wavelengths of light that fall on it.
Methods used in this brief