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KS4 Waves : Sound

KS4 Waves : Sound. Teacher’s Notes. A slide contains teacher’s notes wherever this icon is displayed - To access these notes go to ‘Notes Page View’ (PowerPoint 97) or ‘Normal View’ (PowerPoint 2000). Notes Page View. Normal View. Flash Files.

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KS4 Waves : Sound

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  1. KS4 Waves : Sound

  2. Teacher’s Notes A slide contains teacher’s notes wherever this icon is displayed - To access these notes go to ‘Notes Page View’ (PowerPoint 97) or ‘Normal View’ (PowerPoint 2000). Notes Page View Normal View Flash Files A flash file has been embedded into the PowerPoint slide wherever this icon is displayed – These files are not editable.

  3. What causes sound? Take a tuning fork and strike it against a block of wood, what do you observe? The tuning fork vibrates and you hear a sound. All sounds are caused by vibrations.

  4. Music What vibrates when you sing? Your voice-box. What vibrates when you play a violin? The strings

  5. The Bell-jar experiment What happens when the air is removed from the bell-jar? Sound waves are vibrations and so need a substance to travel through. With air inside, the sound can be heard. With nothing inside [a vacuum], the sound can’t be heard.

  6. Sound : How fast does it travel? You need a quiet open space at least 100m long to perform this investigation. STOP START > 100m 1) When you see the cymbals crash, press START. 2) When you hear the cymbals crash, press STOP.  Write your results in a table like this:

  7. Sound : How fast does it travel?  Calculate your average speed of sound : Av. = [try 1 + try 2 + try 3 + try 4]  4.  What errors could have crept into your results?

  8. Sound : What does it need to travel? • Sound waves need particles in order to travel. • The substance that the sound travels through affects the speed of sound greatly. Speed of sound [m/s]

  9. Travelling sound Sound travels by particles vibrating. To understand this better you need to remember what the particles look like in a solid, liquid and a gas: Which state does sound travel fastest through? Why? solid liquid gas In which state are the particles closest together? Sound travels fastest through solids because the particles are closer together than in a liquid and a gas, so the vibrations are more easily passed from particle to particle. solid In which state are the particles furthest apart? gas

  10. Sound : How fast does it travel? Most of us have seen thunder storms - which comes first, the thunder or lightning? The lightning gets to our eyes before the thunder reaches our ears. 1) Thunder & lightning are made at the same time so we deduce that light travels much faster than sound. 2) In fact light travels so fast that: the time between seeing the flash and hearing the bang = time taken for sound to travel.

  11. Reflection : Echoes You should remember that sound is produced by a vibration and travels as a longitudinal wave ………..and that sound travels at different speeds through different substances [or media] Sound waves reflect off hard, smooth surfaces to produce echoes.

  12. Using echoes What do we call reflected sound? An echo Which surfaces are the best at reflecting sound: HARD or SOFT ? How are echoes reduced in cinemas and theatres? By using soft materials on the walls such as curtains. Name two animals that use echoes? Bats and dolphins

  13. Reflection : Echoes  Stand at least 100m from a large, straight wall. 150m  Measure the distance from you to the wall.  Use a starting pistol [or clapper board] to make a sound.  Measure the time taken between firing the pistol and hearing the echo. START STOP Remember, this is ‘two way travel time’ [twtt]

  14. Reflection : Echoes The sound takes 0.92s to travel 300m. Remember the formula for speed? SPEED = DISTANCE  TIME v = 300  0.92 v = 326 m/s Repeat this several times to obtain an average. For the Higher Tier paper you will need to be able to change the subject of the formula.

  15. Reflection : Questions 120  450  28571 20 Which of these travel faster than the speed of sound in air?

  16. Studying sound Loudspeakers convert the signal from the signal generator into sound waves. The oscilloscope allows us to study the frequency and loudness of a sound. Signal generators can produce signals over a range of frequencies and of varying amplitudes.

  17. Pitch (or frequency) A high pitch sound A low pitch sound. The shorter/longer the wavelength of the wave on the trace; the lower/higher the frequency of the sound. The more waves you can see, the higher the pitch/frequency.

  18. Oscilloscope traces Which trace represents the highest pitched sound? A B ‘A’ is the highest pitched sound because it has the shortest wavelength/most number of waves visible.

  19. Loudness A quiet sound A loud sound The larger/smaller the amplitude of the wave on the trace; the louder/quieter the sound. The bigger the waves you can see, the louder the sound.

  20. Oscilloscope traces Which trace represents the loudest sound? A. B. ‘B’ is the loudest sound because it has the largest amplitude, the larger the amplitude the more energy a wave has, the more energy it has, the louder the sound.

  21. Wave animation

  22. Sound : What can I hear? Increase the frequency of the signal provided by a signal generator whilst keeping the volume the same. 20 The lowest frequency I can hear is ________ Hz The highest frequency I can hear is ________ Hz 20 000

  23. Sound : Are we all the same? You have just found your hearing range - could everyone hear exactly the same frequencies as you? We all have slightly different hearing ranges but almost 1 in 5 people suffer some sort of hearing loss. Temporary hearing loss may be caused by ear infections and colds and hearing recovers. Permanent hearing loss and deafness can be present at birth or occur if the ear is damaged or diseased.

  24. Sound : Are we all the same? Hearing Loss [dB] Hearing is tested using an audiometer and the results are shown on an audiogram.

  25. Sound : Hearing Ranges bats pigeons humans mice elephants moths Which animal can hear the lowest frequency? Which animal can hear the highest frequency? moths pigeons

  26. Sound : The ear 1. Sound waves are collected by the ear lobe or pinna. 6. The auditory nerve takes the signals to the brain. 4. The small bones [ossicles] amplify the vibrations. 3. The waves make the ear drum vibrate. 5. The cochlea turns the vibrations into electrical signals. 2. The waves travel along the ear canal.

  27. Sound : How loud are sounds? 150 140 120 100 80 60 40 20 10 0 Personal stereo Aircraft overhead Permanent ear damage Loud bell A circular saw at 2m Quiet countryside Pin being dropped Can just be heard

  28. What is noise? What you might not consider noise, loud music for example, other people might! A noise is any unwanted sound. What are the effects of noise? 1. _________ 2. _________ 3. _________ 4. _________ Deafness Vomiting Headaches • How can you reduce the effects of loud noise? • _________________ • _________________ • ____________________ _____________________ Nausea Ear protectors Double glazing Putting noisy machinery in insulated rooms

  29. Using Sound Waves : Ultrasound Our ears can’t detect frequencies above 20 kHz. Sound above 20 kHz is called ULTRASOUND.

  30. Using Sound Waves : Ultrasound Ultrasound has many uses, especially in medicine where it is used to scan the fetus. 10 weeks 20 weeks Why do doctors use ultrasound to scan the foetus and not X rays which give a clearer picture? X rays are more energetic and penetrating and are a lot more dangerous, they could cause damage to the growing baby.

  31. Using Sound Waves : Ultrasound Use the internet or research books to find out about other uses of ultrasound. These search terms should help: scans ultrasonic toothbrush dolphin bats jewellery cleaning kidney stones ultrasonic cleaning echo location SONAR

  32. How ultrasound is used? Ultrasound like all sound is reflected different amounts by different materials. A receiver can be used to detect the amount of ultrasound reflected or lost from a signal. A computer can then be used to build up an image of these ultrasound signals. This is how ultrasound is used in prenatal scanning and industrial quality control.

  33. 20 Hz 200 Hz 2 000 Hz 20 000 Hz What is the upper range of human hearing? 

  34. Vibrations Reflections Refractions Heat What causes all sounds? 

  35. Liquid Vacuum Solid Gas Which of the following can sound not travel through? 

  36. 6000m 375m 750m 3000m A ship releases an echo sounding and 4 seconds later receives a signal from the seabed, how deep is the sea? (speed of sound in water is 1500 m/s) 

  37. Prenatal scanning Quality control in industry Cleaning delicate machinery Cooking food Which of the following is not a use of ultrasound? 

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