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The colour of objects

Teaching Guidance for 11-14 Supporting Physics Teaching

Colours come from absorption

Wrong Track: The dress is red because it has that colour and the light in the room brightens it up to let us see it.

Right Lines: The dress is red because when white light falls on it, the dress absorbs many of the frequencies of the spectrum falling on it. The range of frequencies reflected, travelling to your eyes, make the dress appear red.

Colour depends on the light falling on it

Thinking about the learning

For most people, colour is an innate property of an object. For example, a red dress is red simply because it has that colour.

Thinking about the teaching

The idea of the normal colour of an object is an important one here. We can say that the normal colour of any object is the result of white light falling upon it. If the ordinary light is not white light then the object may appear to be a different colour (e.g. in blue light a red dress will appear black).

In other words, the apparent colour of an object depends on the colour of the light entering the eye. This depends not only on the pigments that colour the object, but also on the light which illuminates that object.

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