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Light and Sound

Light and Sound. In this unit: Properties of light Reflection Colours Refraction Properties of sound Hearing. Laser. Part 1 – Properties of Light. Light travels in straight lines:. Light travels VERY FAST – around 300,000 kilometres per second.

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Light and Sound

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  1. Light and Sound • In this unit: • Properties of light • Reflection • Colours • Refraction • Properties of sound • Hearing

  2. Laser Part 1 – Properties of Light • Light travels in straight lines:

  3. Light travels VERY FAST – around 300,000 kilometres per second. At this speed it can go around the world 8 times in one second.

  4. Thunder and lightning start at the same time, but we will see the lightning first. • Light travels much faster than sound. For example: • 2) When a starting pistol is fired we see the smoke first and then hear the bang.

  5. We see things because they reflect light into our eyes: Homework

  6. Properties of Light summary • Light travels in straight lines • Light travels much faster than sound • We see things because they reflect light into our eyes

  7. Part 2 - Reflection Normal • Reflection from a mirror: Reflected ray Incident ray Angle of reflection Angle of incidence Mirror

  8. Angle of incidence = Angle of reflection • The Law of Reflection In other words, light gets reflected from a surface at ____ _____ angle it hits it. The same !!!

  9. Clear vs. Diffuse Reflection • Smooth, shiny surfaces have a clear reflection: Rough, dull surfaces have a diffuse reflection. Diffuse reflection is when light is scattered in different directions

  10. Using mirrors • Two examples: 2) A car headlight 1) A periscope

  11. Refraction Refraction is when waves ____ __ or slow down due to travelling in a different _________. A medium is something that waves will travel through. When a pen is placed in water it looks like this: In this case the light rays are slowed down by the water and are _____, causing the pen to look odd. The two mediums in this example are ______ and _______. Words – speed up, water, air, bent

  12. The Behavior of Waves 10.3 Diffraction • Diffraction occurs when an object causes a wave to change direction and bend around it. • Refraction occurs when waves pass through an object, • Diffraction occurs when waves pass around an object.

  13. The Behavior of Waves 10.3 Diffraction • Waves also can be diffracted when they pass through a narrow opening. • After they pass through the opening, the waves spread out.

  14. The Behavior of Waves 10.3 Reaction of light waves 1. bounce off/ be reflected. 2. If the object is transparent, can be refracted as they pass through 3. The waves can bend around the object.

  15. 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.

  16. The colours of the rainbow: • Red • Orange • Yellow • Green • Blue • Indigo • Violet

  17. Homework 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

  18. A pair of purple trousers 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 seven colours: White light

  19. Using coloured light • If we look at a coloured object in coloured light we see something different. For example, consider a football kit: Shirt looks red White light Shorts look blue

  20. Red light Shirt looks red • In different colours of light this kit would look different: Shorts look black Shirt looks black Blue light Shorts look blue

  21. Other sound effects… • Like light, sound can be… • Reflected – sound reflections are called ______. • Refracted – this is why you might sound strange if you try talking underwater

  22. The Behavior of Waves 10.3 Interference • two or more waves overlap and combine to form a new wave, the process is called interference. Interference occurs while two waves are overlapping.

  23. The Behavior of Waves 10.3 1. Constructive Interference • In constructive interference, the waves add together.

  24. The Behavior of Waves 10.3 2. Destructive Interference • In destructive interference, the waves subtract from each other as they overlap.

  25. Section Check 10.3 Question 1 State the law of reflection. Answer

  26. Section Check 10.3 Question 2 __________ is the bending of a wave caused by a change in its speed as it moves from one medium to another. A. diffraction B. diffusion C. refraction D. reflection

  27. Section Check 10.3 Question 3 Which is the means by which you can hear around corners? A. diffraction B. diffusion C. reflection D. refraction

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