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Where does light come from? The SUN!! The sun is a star located 1.50 x 108, or 1 Astronomical Unit., away from Earth. It provides energy in the form of light through a process called nuclear fusion. Nuclear fusion occurs when two atoms that naturally repelled each other are pulled together by a superior force and the atoms fuse together. The sun’s enormous gravitational force pulls hydrogen atoms together where they fuse to form a helium atom. We then get energy in the form of light and heat. • The sun provides the energy that enables life on Earth. Properties of Light • Light travels in straight lines: Laser • Light travels VERY FAST – 3.0 x 10^8m/s = 300,000 kilometres per second. At this speed it can go around the world 7.5 times in one second. • Light travels much faster than sound. For example: 1) Thunder and lightning start at the same time, but we will see the lightning first. 2) When a starting pistol is fired we see the smoke first and then hear the bang. • We see things because they reflect light into our eyes: Homework • Luminous and non-luminous objects A luminous object is one that produces light. A non-luminous object is one that reflects light. • Shadows Shadows are places where light is “blocked”: Properties of Light summary 1) Light travels in straight lines 2) Light travels much faster than sound 3) We see things because they reflect light into our eyes 4) Shadows are formed when light is blocked by an object History • Unlike heat energy which requires a and sound (a physical substance) to move, light does not • Light is transferred through radiation in a vacuum at the speed of light (3.0X108 m/s) • Light is therefore classified as an Electromagnetic Wave Modern electromagnetic waves • Today we have identified many types of electromagnetic waves which makes up our electromagnetic spectrum. Eureka Video - Radiation Spectrum Modern View Continued As we decrease wavelength, we increase frequency and energy The Visible Light Spectrum • Different colours have different wavelengths! The Surprising Universe • Today Scientists use different portions of the electromagnetic spectrum to collect and analyze data about stars and galaxies • This provides them with completely different views compared with using visible light only http://spaceplace.nasa.gov/en/kids/sirtf1/sirtf_action.shtml The Surprising Universe Essential Knowledge, Skills, and Processes • Analyze the effects of a prism on white light and describe why this occurs. Explain why a rainbow occurs. Answer: different colors have different wavelengths which bend differently as they pass through the prism. http://www.physicslessons.com/exp33.htm Colour • White light is not a single colour; it is made up of a mixture of the seven colours of the rainbow. We can demonstrate this by splitting white light with a prism: This is how rainbows are formed: sunlight is split up by raindrops. The colours of the rainbow: • Red • Orange • Yellow • Green • Blue • Indigo • Violet Prisms • What happens when you place two prisms next to each other? http://micro.magnet.fsu.edu/primer/java/scienceopticsu/newton/ Adding colours • White light can be split up to make separate colours. These colours can be added together again. • The primary colours of light are red, blue, green: Adding blue and red makes magenta (purple) Adding red and green makes yellow Adding blue and green makes cyan (light blue) Adding all three makes white again Colour Adding and Subtracting • http://www.physicslessons.com/exp35.htm Seeing colour • The colour an object appears depends on the colours of light it reflects For example, a red book only reflects red light: White light Only red light is reflected A pair of purple pants would reflect purple light (and red and blue, as purple is made up of red and blue): Purple light A white hat would reflect all the colours: White light Using coloured light • If we look at a coloured object in coloured light we see something different. For example, consider a soccer uniform: Shirt looks red White light Shorts look blue • In different colours of light this uniform would look different: Red Shirt looks red light Shorts look black Shirt looks black Blue light Shorts look blue Using filters • Filters can be used to “” out different colours of light: Red Filter Magenta Filter