4.2 Properties of Visible Light Key Terms Light Reflection Refraction spectrum Visible light Wave model of light Why study waves? Waves transmit energy/ a way of energy to travel. Light is a form of energy. We can use a wave model to describe how light travels. Light is a type of wave you can see. (c) McGraw Hill Ryerson 2007

How does light travel? A model is a way of representing something in order to understand it better and to make predictions. (c) McGraw Hill Ryerson 2007

4.2 Properties of Visible Light A model is a way of representing something in order to understand it better and to make predictions. The wave model of light describes light as a type of wave that travels through empty space. Light transfers energy from one location to another, such as from the Sun to the Earth. A form of wave energy we can see is Visible light. See pages 144 - 145 (c) McGraw Hill Ryerson 2007

4.2 Properties of Visible Light Light transfers energy from one location to another, such as from the Sun to the Earth. A form of wave energy we can see is Visible light. See pages 144 - 145 (c) McGraw Hill Ryerson 2007

What’s happening here? When running on the beach and hit the water, can you run the same speed. Air is a medium, so is water. (c) McGraw Hill Ryerson 2007

Refraction of Light When light passes through different mediums (materials), its speed (frequency) changes, causing the light waves to bend. The bending of waves due to a change in its speed (frequency) is called refraction. Light waves refract (bend) when they pass from one material to another. (c) McGraw Hill Ryerson 2007

A light wave also refracts when it passes through a Prism. Refraction of Light A light wave also refracts when it passes through a Prism. (c) McGraw Hill Ryerson 2007

Colour Activity Play with prisms Colour Wheel (c) McGraw Hill Ryerson 2007

What colour(s) do you see when the colour wheel spins? Regroup What colour(s) do you see when the colour wheel spins? What colour(s) do you see when you shine a light through a prism? (c) McGraw Hill Ryerson 2007

At one time people believed that colour was something added to light. Story of Isaac At one time people believed that colour was something added to light. When white light struck a green leaf, people believed that leaf was adding green to the light. Story of Isaac. At one time people thought colour was something added to light. Green leaf added green to the light. (c) McGraw Hill Ryerson 2007

Producing Visible Spectrum In the 17th century, Sir Isaac Newton did an experiment to prove that light contains colours. He used a prism to separate white light into a spectrum of colours. Story of Isaac. At one time people thought colour was something added to light. Green leaf added green to the light. (c) McGraw Hill Ryerson 2007

When white light travelled through the prism, he saw bands of colour. Isaac Newton When white light travelled through the prism, he saw bands of colour. He observed each colour refracted at different angles. He concluded that the prism was not the source of the colours, that the different colours were already present in the white light. (c) McGraw Hill Ryerson 2007

Producing Visible Spectrum He then used a reverse prism to combine the colours into white light again. Story of Isaac. At one time people thought colour was something added to light. Green leaf added green to the light. (c) McGraw Hill Ryerson 2007

Producing Visible Spectrum He showed that colour was a part of visible light. He proposed that white light, such as sunlight, is the result of mixing together all the different colours of light. (c) McGraw Hill Ryerson 2007

Producing the Visible Spectrum A prism causes white light to split into a spectrum. White light, such as sunlight, is the result of mixing together all the different colours of light. See page 147 (c) McGraw Hill Ryerson 2007

Summary Isaac Newton proved visible light was all colours by passing a beam of light through a prism, and finding the white light separated into its component colours because each colour has different wavelengths. Each wavelength refracts differently, allowing them to separate. (c) McGraw Hill Ryerson 2007

Longer wavelengths are refracted less than shorter wavelengths. White Light White light is made up of waves of different wavelengths and frequencies. The different wavelengths are refracted by different amount, causing them to separate. Longer wavelengths are refracted less than shorter wavelengths. (c) McGraw Hill Ryerson 2007

Colours of the Rainbow When white light is separated into its different colours, this band of colour is called the visible spectrum. The seven most visible colours of the spectrum are: Red, Orange, Yellow, Green, Blue, Indigo, Violet. (ROY G BIV) See page 146 (c) McGraw Hill Ryerson 2007

Which colour has the longest wavelength? (c) McGraw Hill Ryerson 2007

The colour red has the longest wavelength and lowest frequency. The colour violet has the shortest wavelength and highest frequency. (c) McGraw Hill Ryerson 2007

Activity 4-6 p149 Lights, CD, filters (c) McGraw Hill Ryerson 2007

Reflection occurs when light bounces off an object. Colour and Reflection Reflection occurs when light bounces off an object. When white light strikes an object, some colours are reflected and some are absorbed. Only the reflected colours can be seen. For example, yellow cloth reflects yellow and absorbs all other colours. See page 148 (c) McGraw Hill Ryerson 2007

ADDITIVE PRIMARY COLOURS Only three colours of light are needed to produce all the colours of the rainbow: red, green and blue. They are called the three additive primary colours because adding all three together in proper amounts will make white light. Yellow, Magenta and Cyan. (c) McGraw Hill Ryerson 2007

Additive Primary Colours The light of two additive primary colours will produce a secondary color. The three secondary colours are yellow, cyan, magenta. (c) McGraw Hill Ryerson 2007

Check your Understanding p151 #1, 2, 3, 4, 5, 6a, 9, 10, 12 Homework Check your Understanding p151 #1, 2, 3, 4, 5, 6a, 9, 10, 12 (c) McGraw Hill Ryerson 2007