Colour and Light
How are rainbows made? What makes grass green and jeans blue? How do sunglasses work? In this series of demonstrations and activities, students will explore how colours are created and understood by our brain.
This resource also demonstrates numerous ways of producing/revealing colour through chemical reactions, mixing different colours of light, mixing pigments, and chromatography. Students will develop an appreciation for the complexity of something we take for granted: colour.
- Name colour change as one of the possible outcomes of a chemical reaction.
- Describe how different colours of light mix to give new colours.
- Perform methods to separate colours.
- Explain how polarizing filters work and their use in our daily lives.
White light is made up of light with a range of different wavelengths, known as the visual spectrum. Every colour that we can see has a different wavelength and energy.
The back wall of the human eye (the retina) has two kinds of receptors for perceiving light: rods and cones. Rods respond to all wavelengths of the visible spectrum in low light conditions. They allow us to see objects in dim lighting conditions. Cones, on the other hand, respond to certain wavelengths, sending colour information to the brain. There are three different types of cone receptors for coloured light: one is most sensitive to red light, one to green light, and one to blue light. With these three colour receptors we are able to distinguish millions of colours. Cones are less sensitive than rods, requiring higher levels of light. This is why it is difficult to make out the colour of objects in low light conditions.
In order to see colours, there must be at least a little bit of light. White light is actually made of all colours, but the colours you see depend on the amount and colour of light being reflected (thrown back) or absorbed (taken in) by an object.
A red apple looks red because white light, either from light bulbs or from the Sun, hits the surface and all of the colours are absorbed except the red which is reflected back to your eye. Special cells in the back of your eye called cones get "excited" when they are hit by red light and send electrical signals to your brain.
Ordinarily, light waves vibrate in every plane and direction. Polarized light is light that is only vibrating in one plane. A polarizing lens permits only light vibrating in one plane to pass. Polarizing lenses are used on cameras and sunglasses to block the horizontal glare that is produced on reflective surfaces such as lakes.
A rainbow is formed when white light passes through rain droplets. Since different colours contained in white light have different wavelengths, they are refracted through the droplets at different angles, and the colours are separated. Artificial rainbows can be created in class by shining a light source through a clear glass of water — the same process occurs as in a rainbow seen outside.
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