Incident - Light, Colour, Vision

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The normal is an imaginary line drawn on a ray diagram perpendicular to, so at a right angle (90 degrees), to the boundary between two media.

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Yes! Refraction takes place as light crosses the boundary between one transparent medium and another with a different refractive index.

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Yes! Refraction takes place as light crosses the boundary between one transparent medium and another with a different refractive index.

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A human observer is a person who watches something from their own unique point of view.

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Yes! Light becomes diffused as it is transmitted through a medium or is reflected off its surface because of the effect of the scattering of light.

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Total internal reflection means that all the light propagating through a medium is reflected when it reaches its boundary.

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The reflectance of a surface refers to its effectiveness at reflecting light.

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Yes! The angle of incidence of a ray of light as it strikes a surface is always the same as the angle of reflection.

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In the field of optics, diffusion refers to the scattering of light as a result of reflection or transmission.

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No! Human vision relies on trichromacy which is not the same as the RGB colour system.

However, when red, green and blue light is mixed together in different proportions the human eye sees all the colours of the visible spectrum.

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A non-spectral colour is any colour that is not be produced by a single wavelength of visible light.

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Yes! The wavelength and speed of light a ray of light change as they travel through different media.

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The refractive index of a medium is calculated by dividing the speed of light in a vacuum by the speed of light as it propagates through another medium.

So the refractive index of a vacuum = 1 because the speed of light in a vacuum divided by the speed of light in a vacuum = 1.

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The angle between the electric and magnetic field is 90 degrees.

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Infrared and ultraviolet are forms of electromagnetic radiation with wavelengths just outside the visible spectrum.

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The unit used to measure wavelength is the metre.

Because the size of electromagnetic waves varies, different prefixes are used to aid measurement. Here are six examples: kilometre, centimetre, millimetre, micrometre, nanometre and picometre.

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The frequency of incident light is unchanged as it travels from air into glass so its colour remains the same.

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The unit used to measure the frequency of light is the hertz.

The frequency of visible light corresponds to a band of frequencies in the vicinity of 430–770 terahertz (THz)! There are a trillion (1,000,000,000,000) terahertz in a hertz!

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Yes! As the frequency of oscillations of an electromagnetic wave increases the wavelength decreases.

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Yes! Energy increases with frequency.

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Violet has the highest frequency of visible light.

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There are 1000 Kilohertz in one Hertz.

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The hertz is used to measure the frequency of electromagnetic waves!

Because the frequency of electromagnetic waves varies enormously, different prefixes are used to aid measurement. Here are four examples: Kilohertz, megahertz, gigahertz and terahertz!

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There are trillion (1,000,000,000,000) picometres in a metre.

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Yes! Gamma rays have the shortest wavelengths within the electromagnetic spectrum.

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Gamma rays have a shorter wavelength than radio waves.

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Yes! Waves with lower frequencies have longer wavelengths.

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The unit used to measure the wavelengths of visible light is the nanometre.

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In the case of light waves, to propagate means to travels through a medium in a particular direction.

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An electromagnetic wave is the result of the interaction of electric and magnetic fields.

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Yes! A wave with lower frequency has a longer wavelength.

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Gamma rays transport more energy than any other band of wavelengths within the electromagnetic spectrum.

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Gamma rays have the shortest wavelengths of any type of radiation within the electromagnetic spectrum.

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The unit used to measure wavelength is the metre. Because the size of electromagnetic waves varies, different prefixes are used to aid measurement. Here are six examples: kilometre, centimetre, millimetre, micrometre, nanometre and picometre.

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The range of wavelengths that correspond with green is between 570 – 495 nanometres.

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Red has the longest wavelength whilst violet has the shortest.

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Yes! Wavelength is measured in nanometres.

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Yes! The colour of visible light depends on its wavelength.

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Yes! A light wave is another name for an electromagnetic wave! But remember that not all forms of light are visible to the human eye.

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When white light strikes an object, its colour is determined by which wavelengths of light are absorbed and which wavelengths are reflected towards the observer.

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The ball is painted cyan! (Now check out the next question).

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Sunshine is important to human beings because without light we can’t see.

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Sunlight can be described in terms of both waves and particles.

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Too much ultra-violet radiation causes sunburn.

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Yes! The energy that the sun emits is called electromagnetic radiation.

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No! Light only becomes visible when it strikes a medium or object.

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No! The visible spectrum is just the small part of the electromagnetic spectrum our eyes are tuned to.

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Because different wavelengths of light are reflected off the surface of objects. Every surface has unique properties.

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Wavelengths visible to the eye are in a band between approximately 390 to 700 nanometres.

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Yes! Visible light is a form of electromagnetic radiation.

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Red, orange, yellow, green, blue and violet are the bands of colour we see in a rainbow.

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Red is the band of colour with the longest wavelength.

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Violet is the band of colour with the shortest wavelength.

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nm is shorthand for nanometre.

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Rainbows produce spectral colours as sunlight is refracted by raindrops.

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The invisible band of wavelengths next to red is infrared.

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Yes! Each wavelength of light corresponds with a different colour seen by an observer.

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The unit of measurement for wavelengths of visible light is the nanometre (nm).

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When wavelengths of light corresponding with red, green and blue are projected at equal intensity onto a dark surface it appears white to an observer.

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White light contains all the wavelengths of the visible spectrum at equal intensity.

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Yes! Because the Sun radiates light at all wavelengths of the electromagnetic spectrum it therefore also emits light at all wavelengths of the visible spectrum.

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The Sun radiates light at all wavelengths of the electromagnetic spectrum.

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Yes! As the frequency of oscillations of an electromagnetic wave increase the wavelength decreases.

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Yes! Energy increases with frequency.

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Hertz. Kilohertz. Megahertz. Gigahertz. Terahertz.

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A light wave in a vacuum travels at 300,000 kilometres (km) per second! Or to be exact, 299,792 km/sec.

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Yes! A wave-cycle can be measured from any point on a wave to the same point on the next wave.

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The lowest point in the oscillation of a wave is called the trough.

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Yes! light waves propagate through a vacuum in a straight line.

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Blue and violet are two of the colours with the shortest wavelengths.

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Red and orange are two of the colours with the longest wavelengths.

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Some estimates of the number of colours the human eye can distinguish between run into the millions.

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Yes! Every wavelength of light corresponds with a different colour.

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Our eyes are tuned to visible light – the visible part of the electromagnetic spectrum.

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Names for solar radiation include solar energy and light.

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The sun emits electromagnetic radiation.

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The sun generates energy as a result of thermonuclear fusion.

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The star at the centre of our solar system is called the Sun.

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Gamma rays have a higher frequency than any type of electromagnetic radiation.

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Gamma rays transport more energy than any other form of electromagnetic radiation.

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Shorter wavelengths = Higher frequency.

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Lower frequency = Longer wavelengths.

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Yes! The speed of light is affected by the medium through which it propagates.

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The maximum speed of light occurs in a vacuum! Light travels in air at 99% of the speed of light in a vacuum.

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No! Both crown glass and diamonds are slow media because they significantly reduce the speed of light.

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No! The colour of a ray of light remains the same because frequency doesn’t change as light travels through different media.

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Millimetres, centimetres, metres and kilometres are all used to measure the wavelengths of radio waves.

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RGB refers to the colours red, green and blue. These are the primary colours used by the RGB colour model to mix wavelengths of light to produce a palette of as many as 16 million colours.

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ROYGBV refers to red, orange, yellow, green, blue and violet. ROYGBV are the spectral colours associated with rainbows and the diffusion of white light.

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The visible spectrum is the small part of the electromagnetic spectrum our eyes are tuned to.

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White light is the name for light containing all the wavelengths of the visible spectrum.

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A continuous spectrum is produced by an inclusive band of wavelengths of light between any two points on the electromagnetic spectrum.

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Additive primary colours are three wavelengths of light that produce white when combined together in equal proportions.

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Red, green and blue are the three additive primary colours used in the RGB colour model.

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Yes! Every spectral colour corresponds with a single wavelength of visible light.

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The visible spectrum includes all the wavelengths of light the human eye is sensitive to and results in the colours we see between red and violet.

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Additive primary colours are three wavelengths of light that produce white when combined together in equal proportions.

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Spectral colours are all the colours between red and violet that can be produced by a single wavelength of light. Sunlight is composed of spectral colours.

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A typical human eye will respond to wavelengths between 390 to 700 nanometers.

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Yes! Each colour in a rainbow between red and violet is a spectral colour.

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No! The colours produced by mixing RGB primary colours are not spectral colours because they are not produced by a single wavelength of light.

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RGB is a colour model used to produce a full palette of colours by mixing red, green and blue light sources in different proportions.

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Secondary colours are the colours produced by mixing pairs of primary colours in equal proportions. The RGB secondary colours are cyan, magenta and yellow.

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Yes! ROYGBV are all spectral colours and so each can be produced by a single wavelength of light between 480 and 700 nanometres.

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Yes! ROYGBV are all spectral colours and so can be produced by a single wavelength of light.

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Yes! Spectral colours can be combined together to produce orange, yellow and violet in the correct proportions.

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Cone cells are the light-sensitive neurons in the retina at the back of our eyeballs.

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When red (660 nm), green (525 nm) and blue (460 nm) colours of light are projected at the same intensity onto a neutral coloured surface they produce white.

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Cyan, magenta and yellow are the three primary colours used for digital printing. They are subtractive primaries, so mixed together they produce black.

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When wavelengths corresponding with red, green and blue are projected onto a neutral coloured surface they produce white.

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Red, green and blue are the three primary colours in the RGB colour model.

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There are 6 tertiary colours in the RGB colour model! They result from mixing a primary and secondary colour. So a tertiary colour is produced by mixing red-yellow or green-cyan etc.

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An RGB colour wheel is a way of exploring the relationship between red, green and blue primary colours when they are mixed to produce secondary and tertiary colours etc.

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Spectral colours are the colours produced by different wavelengths of light. Sunlight and rainbows are composed of spectral colours. RGB colour is an additive colour model in which red, green and blue light is combined in various proportions to produce the appearance of other colours.

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Red and green are the two primary colours of light that together make yellow.

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When spectral colours are arranged in a diagram, the order in which they appear corresponds with their wavelength and so their place in the visible part of the electromagnetic spectrum.

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A computer screen uses the RGB colour model. Each pixel contains three tiny semiconductors that produce red, green and blue light! The colour we see changes as the intensity of light produced by each semiconductor increases or decreases!

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Because a colour wheel demonstrates the effect of mixing different proportions of the three RGB primary colours – red, green and blue!

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Cyan is a secondary colour in the RGB colour model!

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In the RGB colour model green and blue are the two primary colours that together make cyan!

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Yes! Cyan is a spectral colour with a wavelength of around 510 nanometres (nm).

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Magenta is a secondary colour in the RGB colour model.

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A printer that uses CMYK inks adds black (K) ink to cyan, magenta and yellow to produce deeper blacks.

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No! There is no single wavelength in the visible spectrum that corresponds with magenta.

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Cyan is a primary colour in the CMY colour model.

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Blue and red are the two primary RGB colours that together make magenta!

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When wavelengths corresponding with red, green and blue are projected onto a neutral coloured surface in equal proportions they produce white.

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Inks corresponding with the three CMY primary colours produce black during printing because each colour subtracts from the wavelengths of light reflected off the paper towards an observer.

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Overlapping wavelengths of light corresponding with cyan, magenta and yellow make white because, when reflected off a neutral coloured surface, each adds more wavelengths to the reflected light.

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There are three primary colours in an RGB colour wheel.

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There are twelve tertiary colours in an RGB colour wheel with eighteen colours.

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Yes! All RGB colour wheels start with the three primary colours: red green and blue.

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Yes! There are always secondary colours between primary colours.

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No! Because of the way colour wheels divide up when using decimal or hexadecimal notation, the intermediary colours between secondaries do not always include tertiary colours. Tertiary colours are produced by using equal proportions of secondary colours.

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Yes! Every colour on a colour wheel is produced by mixing equal proportions of the colours on either side.

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Red, green and blue are the three primary colours used when building an RGB colour wheel.

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Cyan, magenta and yellow are the three secondary colours when building an RGB colour wheel.

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Yes! Equal proportions of primary colours are used to produce secondary colours.

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Yes! Every colour in a colour wheel can be produced by mixing different proportions of red, green and blue primary colours.

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The wavelength of an electromagnetic wave is a measurement of the length of a single oscillation of the wave.

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The frequency of an electromagnetic wave is a measurement of the number of wave oscillations passing a given point in a given period of time.

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Frequency of an electromagnetic wave in a vacuum is calculated by dividing the speed of light by the wavelength of the wave.

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Yes! The speed of light depends on the optical density of the medium it is propagating through.

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300,000 kilometres per second.

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A ray is a narrow beam of light from a point light source. In a ray diagram, a light ray is a way of tracing the motion of light, including its direction of travel, and what happens when it encounters different media.

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Incident light refers to incoming light that is travelling towards an object or medium.

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Reflection takes place when incoming light strikes the surface of a medium, some wavelengths are obstructed, and the wavefront bounces off and returns into the medium from which it originated.

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Refraction refers to the way light changes speed and direction as it travels across the interface between one transparent medium to another.

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A medium is any transparent material through which an electromagnetic wave propagates (plural media).

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As light travels from a fast medium such as air to a slow medium such as water it bends toward ‘the normal’ and slows down. As light passes from a slow medium such as diamond to a faster medium such as glass it bends away from ‘the normal’ and speeds up.

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Snell’s law deals with changes in the angle of incidence and angle of refraction as light travels through different media.

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Refractive index (index of refraction) is a measure of how much slower light travels through a given medium than through a vacuum.

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The refractive index of a medium is calculated by dividing the speed of light in a vacuum by the speed of light in another medium.

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When light crosses a boundary into a medium with a high refractive index (eg. diamond = 2.42) there is a significant change in direction.

When light crosses a boundary into a medium with a low refractive index (eg. water = 1.333) there is a less significant change in direction.

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Index of refraction is the other term used for refractive index.

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Snell’s law is the other term used for the law of refraction.

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In mathematics, the sine of an angle within a triangle is produced by calculating the ratio of the length of the side that is opposite that angle to the length of the longest side of the triangle (the hypotenuse).

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The angle of refraction as light crosses their boundary.

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Chromatic dispersion refers to the way that light separates into its component wavelengths (and so colours), under certain conditions.

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Every wavelength of light is affected to a different degree by the refractive index of a material and as a result changes direction by a different amount when passing from one medium (such as air) to another (such as glass).

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Yes! As light crosses the boundary from one medium to another through which it travels more slowly, then it will bend towards the normal.

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The angles of incidence and reflection are measured between each ray and the normal.

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Yes! Light travels faster in air than in glass.

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Yes! Every wavelength of light is affected to a different degree by the refractive index of a material and as a result, changes direction by a different amount when passing from one medium to another.

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The wavelength of incident light decreases as it travels from air into glass.

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Magenta is a primary colour in the CMY colour model.

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Red, yellow and blue primary colours produce a dark brown when mixed together because each colour subtracts from the wavelengths of light reflected towards an observer.

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Both are subtractive colour models. Subtractive colour models such as CMY or RYB are used for mixing paints, pigments, inks and dyes.

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Red, yellow and blue are the three primary colours used with the RYB colour model.

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The RYB colour model is a subtractive colour model widely used for mixing artists paints and introducing colour to children. It is well suited to powder, acrylic and oil paints.

How to use the Colour Finders

Use a desktop or laptop computer to view these Colour Finders
Select the Colour Finder you want to explore
The Colour Finder will open in the Image Library
Select the Finder again to open it as a PDF in your Browser
Select FULL-SCREEN MODE in your Browser
Use arrow keys [< or >] to move from page to page

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The frequency of a wave is a measurement of the number of waves passing a given point in a given period of time!

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Other names for sunlight include daylight, sunshine, visible light, light and electromagnetic radiation!

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All forms of light travel at 299,792 kilometres per second in a vacuum (almost 300,000 km/sec)!

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The largest unit used to measure the wavelength of electromagnetic waves is the kilometre!

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There are six secondary colours in an RGB colour wheel with six colours!

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Orange, green and purple are the RYB secondary colours.

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A subtractive colour model helps to make sense of what happens when different coloured pigments (eg. paints, inks, dyes or powders) are mixed together to produce other colours.

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