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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. A luminous object is one that produces light. A non-luminous object is one that reflects light. • Luminous and non-luminous objects Luminous objects Reflectors

  7. Rays of light Shadows are places where light is “blocked”: • Shadows

  8. 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 • Shadows are formed when light is blocked by an object

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

  10. 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 !!!

  11. 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

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

  13. 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.

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

  15. 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 and green: Adding blue and red makes magenta (purple) Adding blue and green makes cyan (light blue) Adding red and green makes yellow Adding all three makes white again

  16. 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

  17. 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

  18. 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

  19. 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

  20. Homework Some further examples:

  21. Red Filter Magenta Filter Using filters • Filters can be used to “block” out different colours of light:

  22. Investigating filters

  23. Red Blue Green White Yellow Cyan Magenta

  24. 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

  25. Sound – The basics We hear things when they vibrate. If something vibrates with a high frequency (vibrates very ______) we say it has a _____ pitch. If something vibrates with a low frequency (vibrates ______) we say it has a ____ pitch. The lowest frequency I could hear was… Words – slowly, low, high, quickly

  26. Drawing sounds… This sound wave has a _____ frequency: This sound wave has a ___ _frequency:

  27. Drawing sounds… This sound wave has a _____ amplitude (loud): This sound wave has a _____ amplitude (quiet):

  28. Hearing problems • Our hearing range can be damaged by several things: • Too much ear wax! • Damage to the auditory nerve • Illness or infections • Old age (not like Mr Richards)

  29. 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

  30. The Ear Label your diagram with the following: These bones are vibrated by the eardrum This tube carries the sound towards the eardrum This part is used to help us keep our balance This part “picks up” the vibrations This part of the ear contains many small hairs with turn vibrations into an electrical signal This part connects the ear to the mouth This part “channels” the sound towards the ear drum

  31. The Ear