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Sound and Light QuickTime™ and a decompressor are needed to see this picture. Yr 8 Science In This Topic you should be able to: Describe and identify energy changes in situations involving light and sound Describe sound as a form of energy requiring a medium (matter) to travel through Describe light energy as a form of energy requiring a no medium to travel through Explain the difference between a noise and a musical note Describe how musical instruments work and how music is recorded Explain the difference between reflection and refraction Understand how lenses work Explain why objects have colour Facts! More than 90% of the information we receive reaches our senses as a type of energy detected by our eyes (light energy) or ears (sound energy). It takes 8 minutes for the light to travel from the sun to Earth but only a millionth of a second to travel a football field. Measuring sound Try these things at home QuickTime™ and a decompressor are needed to see this picture. QuickTime™ and a decompressor are needed to see this picture. Measuring Sound The frequency of sound (measured in Hertz) is also called the pitch. An example of a high pitched sound ________________ An example of a low pitched sound ________________ This frequency is a measure of the vibrations per second. A sound with a high pitch has more vibrations and the waves are closer together! http://www.youtube.com/watch?v=lKaQzgwxy Vg - Octave Wave Forms Mozzie Ringtones Your teacher will play a variety of frequencies starting at 8000 hertz and increasing to 18,000 hertz. List each frequency and tick whether you can hear it. E.g. 8000 Hz 18,000 Hz Qu i ck Ti me ™a nd a de co mp re ss or a re ne ed ed to s ee th i s pi c tu re. Quic kTime™ and a dec ompres sor are needed to see this pic ture. The speed that sound travels at is much slower than (about 1/3rd km a second) that of light (300,000 km a second). A timer who stands a long way from the starter’s gun will start timing when he sees smoke rather than listening to the sound. Can you think of another example of when we see something and hear the associated sound after? We often hear thunder after the lightening even though they occur at the same time! Every 3 seconds you count between thunder and lightening, tells you that the lightening struck a km away QuickTime™ and a decompressor are needed to see this picture. The Sound of music Noise is a jumble of many sounds. Musical notes are more regular sounds that are pleasing to the ears. These are controlled vibrations in musical instruments. Every musical instruments produces vibrations and has a resonator to produce longer sounds. Musical instruments Choose an instrument Prepare a one page report on how it operates (This can be done in pairs but each student must write a report) Include: A Diagram Detailed description of the parts How sound is produced Which parts vibrate and which parts resonate How the pitch of a note is changed The frequency range How the volume is controlled How to tune the instrument Brainstorm: what instruments do you know? What categories? Percussion Drums, bongos, cymbals, Triangle, clap sticks, chimes Strings Guitar, violin, cello, banjo, piano, bouzki, bass guitar Wind Flute, trumpet, trombone, didgeridoo, bagpipes, piccolo, BENDING AND BOUNCING LIGHT EXPERIMENT What happens when light meets different substances? Clear glass Frosted glass Wood Equipment: A ray box, materials (above) Results Substance Clear Glass Frosted Glass Wood What you can see through the substance? What happened to the Beam of light? Conclusion When light travels through clear glass the beam remains on the same path and is not scattered. When light hits wood it is absorbed, however some light must be reflected because we can see it. When light travels through frosted glass it lost intensity (some light was blocked) and the light was scattered and bent off its original path. QuickTime™ and a decompressor are needed to see this picture. Electromagnetic Spectrum Visible light is part of the Electromagnetic spectrum All light EM waves travel at the speed of light The Wavelength is the distance between two crests of the waves The Amplitudes is the height of the wave. Benefits and Dangers! What do we uses EM waves for? -Transmitting sound and picture signals on Radio waves eg TV’s and Radios. - Heating food in a microwave - Seeing broken bones in an X-ray -Keeping warm using heaters and flames which project infrared rays What are the dangers of EM waves? -Long term exposure to X-rays or Gamma Rays can cause cancers -Skin cancers including melanomas are caused by UV Rays How a Camera works QuickTime™ and a decompressor are needed to see this picture. Thinking activity Using these facts and the diagram of a camera describe how you think a simple camera works: Film is coated in a light-sensitive chemical that changes colour when exposed to light A lens is a curved piece of glass or plastic which focuses light into a single point A shutter in a camera moves very quickly allowing only a split-second exposure to light Every thing we can see has light reflecting off of it. Negatives What do you notice on these negatives? QuickTime™ and a d eco mpres sor are nee ded to s ee this picture . QuickTime™ and a d eco mpres sor are nee ded to s ee this picture . QuickTime™ and a decompressor are needed to see this picture. PHOTOGRAPHS Negatives- The original film material which shows light parts of a photo dark and vice versa. Silver Nitrate crystals go dark when they are exposed to light. An aperture is the size of the hole which allows light into a camera. If a photo has too much light let through the aperture it is considered as over-exposed If a photo is too dull and has too little light coming through its aperture we call it underexposed. In 1666, Isaac Newton discovered that white (visible light) was made up of a spectrum of colours (the rainbow or ROYGBIV) When light was passed through a triangular prism he demonstrated this spectrum. Light through a prism QuickTime™ and a decompressor are needed to see this picture. QuickTime™ and a decompressor are needed to see this picture. What is occurring when we see green grass? What about when light travels through a coloured translucent material like red cellophane?