Colours – Learning Outcomes  Associate the wavelength of light with its colour.  Describe the electromagnetic spectrum in terms of frequency and wavelength.  Detect UV and IR radiation.  Discuss UV radiation and the ozone layer.  Give uses of infrared cameras.  Discuss the greenhouse effect. 1

Colours – Learning Outcomes  Give the primary colours.  Discuss addition of colours, in particular secondary and complementary colours.  Demonstrate addition of colours.  Give uses of colour addition.  Describe the spectrometer and the function of each of its parts.  Demonstrate the spectrometer. 2

Electromagnetic Spectrum  Humans are only able to see some kinds of light.  These kinds of light are known as visible light, with wavelengths between 400 and 700 nm. 3 by Abstruse Goose – CC-BY-NC-3.0

Electromagnetic Spectrum 4 by Jonathan S Urie – CC-BY-SA-3.0

Detecting Ultraviolet  Ultraviolet (UV) light has higher frequency / lower wavelength than visible light.  Causes some objects to fluoresce, e.g. Vaseline, washing powder, bleach. 5  Can affect a photographic plate.  Can cause sunburn.  Produces vitamin D in the skin.  Can cause photoemission.

Ozone Layer  Ozone is a chemical that blocks UV light.  It exists as one of the layers in the atmosphere. 6  Chlorofluorocarbons (CFCs) were used in refrigerants, propellants, and solvents until the 90s.  They were contributing to depletion of the ozone layer, so were banned worldwide. by NASA – public domain

Detecting Infra-red  Infra-red (IR) light has lower frequency and higher wavelength than visible light.  Has a heating effect on many things.  Affects a photographic plate.  Passes through fog. 7 by Elisa dem – CC-BY-SA-4.0  IR cameras are used by military to see in the dark and detect living organisms.  They are also used in medical imaging.

Greenhouse Effect  The Earth absorbs visible sunlight and reradiates it as IR.  Our atmosphere allows visible light to pass through it, but reflects some IR.  Emissions by modern society (particularly carbon dioxide) currently increases the amount of IR that the atmosphere reflects back.  This is called the greenhouse effect and is causing the planet to heat up over time. 8

Colours  Red, green, and blue are primary colours.  Other colours are produced by mixing these colours in different amounts.  Magenta, yellow, and cyan are secondary colours – they are produced by mixing primary colours in equal amounts. 9 by SharkD – public domain

Colours  Complementary colours are pairs of primary and secondary colours that add to produce white light. 10 by SharkD – public domain

Demonstrate Addition of Colours 1.Set up a ray box so that it produces light from three openings. 2.Using colour filters, colour each of the three light sources. 3.Using the mirrors on the ray box, mix colours, noting the resulting colours. 4.Pairs of primary colours produce secondary colours, and pairs of primary and secondary colours produce white light. 11

Uses of Colour Addition  Televisions, computer monitors, tablet computers etc. use colour addition to display.  Each pixel is a combination of a red, a blue, and a green sub-pixel.  Various technologies use different intensities of each colour to make all other colours.  Similarly, stage lighting often uses multiple coloured light sources to produce whatever colour is needed on the stage. 12 by Stan Zurek CC-BY-SA-3.0 by Nicky Nouse public domain

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Spectrometer  Turntable – free to rotate allowing gratings or slits to rotate.  Slit – narrows the beam entering the spectrometer.  Collimator – ensures the light leaves as a parallel beam.  Telescope – allows emergent beams to be examined. Has an angle scale attached that rotates with it.  This apparatus may be asked about in the wavelength of light experiment, where a sodium lamp is used instead of a laser. 14