Sound

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GCSE Physics double award notes

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  • Play ‘F1 BBC 2009 intro’ video clip If there was one common noise that was associated with a car driving past at a high speed it would have to be ‘neeee yyyyooooo’. From that high pitch of the car coming towards you to the low pitch when its speeding off in the other direction. But why is that sound created? Here we have the RB6 F1, Red Bull’s new car launched for the new 2010 season, Mark Webber and Sebastian Vettel who will race in the car for the first time at Bahrain on 13th March
  • Sound travels as a wave, the energy of a vibration is passed along by a longitudinal wave where the air particles experience different pressures, to form compressions and rarefrations. We can use a wavefront diagram to represent these features of a wave (picture one, the sound being emitted from an stationary object). No matter where the listener would be standing the wave passing by would have the same frequency and wavelength. The only thing that the listener might observe is that the further away they are the softer the sound is. For an object creating a sound and also moving while emitting that sound, the listener would have a very different experience (picture two). If the listener is standing in front of the moving object, what is different about the waveform and explain why? (The wavelength is smaller and frequency is greater, this is because the waves are closer together when they reach the listener). What if they are standing behind the loud moving object, again what is different and why? So the sound heard depends on the position of the listener - when the frequency is high or wavelength is short, a high pitch is experienced and for a low frequency, a low pitch is experienced. http://www.lon-capa.org/~mmp/applist/doppler/d.htm http://paws.kettering.edu/~drussell/Demos/doppler/ doppler.html
  • Breaking the sound barrier is when the moving object actually goes faster than the speed of sound - it travels in front of the sound that it emitting. Space shuttles and fighter jet often break the sound barrier and a loud sonic boom indicates the plane is going faster than the sound. Sonic boom is an impulsive noise similar to thunder. It is caused by an object moving faster than sound, about 750 miles per hour at sea level. An aircraft traveling through the atmosphere continuously produces air-pressure waves similar to the water waves caused by a ship's bow. When the aircraft exceeds the speed of sound, these pressure waves combine and form shock waves which travel forward from the generation or "release" point. The sound heard on the ground as a "sonic boom" is the sudden onset and release of pressure after the buildup by the shock wave or "peak overpressure." The change in pressure caused by sonic boom is only a few pounds per square foot, about the same pressure change we experience on an elevator as it descends two or three floors, in a much shorter time period. It is the magnitude of this peak overpressure that describes a sonic boom.
  • One other demo to show the Doppler effect is to spin around an egg timer using a piece of string while it is making a sound – this change in tone or pitch is caused by the different sound waves that each the listener. Some are bunched together, high frequency with a short wavelength and some are spread out, low frequency with a long wavelength.
  • Make use of the video camera hooked up to the data projector. Gather round, lets check out what the CRO is all about. This piece of kit translates the sound wave which hit the drum or diaphragm of the microphone into an electrical signal which is then displayed on the screen. The screen represents a graph of the sound wave where the x-axis indicates time and the y-axis indicates the displacement of the microphone’s diaphragm. Loud speaker with ping-pong ball set on top. Recognise that when a sound is produced it is a vibration of the cone, slowed way down it is possible to see the vibration. What is the relationship between the sound produced and the trace on the CRO? Turn the volume up and down - loudness linked to amplitude Change the number of vibrations per second of the speaker - pitch linked to frequency, wavelength on the trace Back to the speaker hooked up to signal generator, what is the lowest/highest sound that is possible for us to hear? Fill out the notes from the worksheet
  • Sound travels as a wave so there are some common behaviours that we understand by applying what we know about our previous study of wavefronts – in the last lesson, what characteristic of waves did we apply to a sound wave? Amplitude, vibration needed, type of wave (longitudinal) frequency. What will happen when a sound wave hits a surface? It will reflect, bounce off and move away at another angle (equal to that which it was moving towards that surface). Echoes http://www.acoustics.salford.ac.uk/schools/teacher/index.html
  • Is the energy of reflected sound equal to the energy of the incident sound? Why?
  • Ultra-sound Sonography- real time, unlike x-ray radiation, see the movement of the tissue, painless, non-harmful. Scans of- liver gallbladder spleen pancreas kidneys bladder uterus, ovaries, and unborn child (fetus) in pregnant patients eyes thyroid and parathyroid glands scrotum (testicles) Used to -assess damage after a heart attack, guide procedures such as needle biopsies or breast cancer (Process of removing tissue from living patients for diagnostic) http://www.radiologyinfo.org/en/info.cfm?pg=genus&bhcp=1 http://videos.howstuffworks.com/discovery-health/14521-human-atlas-ultrasound-video.htm (after the first 13 seconds…) Notes on previous handout to be filled in!
  • Sonography - real time, unlike x-ray radiation, see the movement of the tissue, painless, non-harmful. Scans of- liver gallbladder spleen pancreas kidneys bladder uterus , ovaries , and unborn child ( fetus ) in pregnant patients eyes thyroid and parathyroid glands scrotum ( testicles ) Used to -assess damage after a heart attack, guide procedures such as needle biopsies or breast cancer (Process of removing tissue from living patients for diagnostic) http://www.radiologyinfo.org/en/info.cfm?pg=genus&bhcp=1
  • Why do bats have eyes?
  • Measuring Speed of sound - Using the cards, re-arrange the order of Tim and Moby’s investigation
  • Sum of attempts = 2.236 s Average time = 0.4472 s S = d / t = 134 / 0.4472 = 299.6 m/s
  • Sound

    1. 1. Sound <ul><li>GCSE Physics </li></ul>
    2. 2. Aims of the lesson <ul><ul><ul><ul><ul><li>To recall how a sound wave is created and travels through a medium </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><li>To state how different sounds can be produced and relate this to the frequency and amplitude of the wave </li></ul></ul></ul></ul>
    3. 4. Doppler Effect
    4. 5. Going Super Sonic
    5. 7. Cathode Ray Oscilloscope
    6. 8. Wave Animation
    7. 9. Complete the CRO traces Original Frequency x2 of Original Frequency x2 and ½ amplitude of Original Exactly the same sound (only a couple of seconds later)
    8. 10. <ul><li>To recall that sound can bounce off surfaces </li></ul><ul><li>To describe how sound waves can be used to detect objects both in industry and medicine </li></ul>Aims of the lesson
    9. 13. Echoes <ul><li>An echo is a reflected sound. When sound is reflected off a plane (or flat) surface- </li></ul><ul><li>Angle of incidence = Angle of reflection </li></ul>Some of the energy of the incident wave will be absorbed when it is reflected by a surface.
    10. 14. Example <ul><li>A fishing boat sends out a pulse of ultra sound. The reflected pulses are detected after 0.8 s and 1.4 s. The speed of ultrasound in water is 1500 m/s. </li></ul><ul><li>Calculate 1.) the depth of the sea bed and 2.) the depth of the shoal of fish. </li></ul>1. Distance x 2 = Speed x Time = 1500 x 1.40 = 2100m 2. Distance x 2 = Speed x Time = 1500 x 0.8 = 1200m The sound travels double the distance so… Distance to sea bed = 2100 / 2 = 1050m Distance to shoal of fish = 1200 / 2 = 600m
    11. 15. http://www.radiologyinfo.org/en/info.cfm?pg=genus&bhcp=1
    12. 16. How is ultrasound used? <ul><li>Ultrasound (> 20000 Hz) like all sound is reflected different amounts by different materials. </li></ul><ul><li>A receiver can be used to detect the amount of ultrasound reflected or lost from a signal. </li></ul><ul><li>A computer can then be used to build up an image of these ultrasound signals. </li></ul><ul><li>This is how ultrasound is used in prenatal scanning and industrial quality control. </li></ul>
    13. 17. <ul><li>How do these animals use sound to aid them? </li></ul>Page 89 and 90
    14. 18. Measuring Speed of sound
    15. 19. The results are in… <ul><li>Using this set of results, calculate the speed of sound in air- </li></ul><ul><li>The exact speed of sound is 330m/s, what errors in the experiment could account for a lesser value? </li></ul>Time (s) 0.425 0.462 0.470 0.432 0.447 Attempt 1 2 3 4 5 Distance = 134m

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