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KS4 Waves : Sound © Boardworks Ltd 2003 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. © Boardworks Ltd 2003 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. © Boardworks Ltd 2003 Music What vibrates when you sing? Your voice-box. What vibrates when you play a violin? The strings © Boardworks Ltd 2003 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. © Boardworks Ltd 2003 Sound : How fast does it travel? You need a quiet open space at least 100m long to perform this investigation. STOP START 00:0000 34 > 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: © Boardworks Ltd 2003 Sound : How fast does it travel? Try Distance [m] Time [s] Speed [m/s] 1. 100 0.34 294 2. 3. 4. Calculate your average speed of sound : Av. = [try 1 + try 2 + try 3 + try 4] 4. What errors could have crept into your results? © Boardworks Ltd 2003 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. 7000 6000 6000 5000 5000 4000 3000 2000 1450 1000 330 350 Air at 0 C Air at 30 C 0 W ater Concrete Steel Material © Boardworks Ltd 2003 Travelling sound Sound travels particles vibrating. Which statebydoes sound travel fastest through? To understand this betterWhy? you need to remember what the particles look like in a solid, liquid and a gas: solid liquid gas In whichtravels Sound state are fastest the through particlessolids closest because together? the particles are closer together than in a liquid and a gas,solid so the vibrations are more easily passed from apart? particle to particle. In which state are the particles furthest gas © Boardworks Ltd 2003 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. © Boardworks Ltd 2003 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. © Boardworks Ltd 2003 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 © Boardworks Ltd 2003 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 START STOP between firing the pistol and hearing the echo. Remember, this is ‘two way travel time’ [twtt] © Boardworks Ltd 2003 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. © Boardworks Ltd 2003 Reflection : Questions Distance [m] Time [s] Speed [m/s] Small aeroplane 600 5 120 Jet fighter 900 2 450 Meteorite 10,000 0.35 28571 Cheetah 50 2.5 20 Which of these travel faster than the speed of sound in air? © Boardworks Ltd 2003 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. © Boardworks Ltd 2003 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. © Boardworks Ltd 2003 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. © Boardworks Ltd 2003 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. © Boardworks Ltd 2003 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. © Boardworks Ltd 2003 Wave animation © Boardworks Ltd 2003 Sound : What can I hear? Increase the frequency of the signal provided by a signal generator whilst keeping the volume the same. 20 Hz The lowest frequency I can hear is ________ 20 000 Hz The highest frequency I can hear is ________ © Boardworks Ltd 2003 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. © Boardworks Ltd 2003 Sound : Are we all the same? Hearing is tested using an audiometer and the results are shown on an audiogram. 80 70 Hearing Loss [dB] 60 50 optimal hearing 40 impaired hearing 30 20 10 0 0 2000 4000 6000 8000 Frequency of sound [Hz] © Boardworks Ltd 2003 Sound : Hearing Ranges Hearing Ranges of Animals bats pigeons humans mice elephants moths 1,000,000 100,000 10,000 1,000 100 10 1 0 Which animal can hear the lowest highest frequency? Frequency [Hz] pigeons moths © Boardworks Ltd 2003 Sound : The ear 1. Sound waves are collected by the ear lobe or pinna. 3. The waves 2. The waves travel along the make the ear drum vibrate. ear canal. 6. The auditory nerve takes the signals to the brain. 4. The small bones [ossicles] amplify the vibrations. 5. The cochlea turns the vibrations into electrical signals. © Boardworks Ltd 2003 Sound : How loud are sounds? Aircraft overhead 150 140 120 Personal stereo Permanent ear damage Loud bell 100 A circular saw at 2m 80 60 40 Quiet countryside 20 Pin being dropped 10 0 Can just be heard © Boardworks Ltd 2003 What is noise? A noise is any unwanted sound. What are the effects of noise? 1. Deafness _________ 2. Vomiting _________ 3. Headaches _________ 4. Nausea _________ What you might not consider noise, loud music for example, other people might! How can you reduce the effects of loud noise? Ear protectors 1._________________ Double glazing 2._________________ Putting noisy machinery 3.____________________ in insulated rooms _____________________ © Boardworks Ltd 2003 Using Sound Waves : Ultrasound Our ears can’t detect frequencies above 20 kHz. Sound above 20 kHz is called ULTRASOUND. © Boardworks Ltd 2003 Using Sound Waves : Ultrasound Ultrasound has many uses, especially in medicine where it is used to scan the fetus. 10 weeks 20 weeks Why doare doctors ultrasound to scan the and foetus X rays more use energetic and penetrating areand a lotnot more X rays whichthey givecould a clearer picture? dangerous, cause damage to the growing baby. © Boardworks Ltd 2003 Using Sound Waves : Ultrasound Use the internet or research books to find out about other uses of ultrasound. These search terms should help: bats © Boardworks Ltd 2003 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. © Boardworks Ltd 2003 What is the upper range of human hearing? A. 20 Hz B. 200 Hz C. 2 000 Hz D. 20 000 Hz © Boardworks Ltd 2003 What causes all sounds? A. Vibrations B. Reflections C. Refractions D. Heat © Boardworks Ltd 2003 Which of the following can sound not travel through? A. Liquid B. Vacuum C. Solid D. Gas © Boardworks Ltd 2003 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) A. 6000m B. 375m C. 750m D. 3000m © Boardworks Ltd 2003 Which of the following is not a use of ultrasound? A. Prenatal scanning B. Quality control in industry C. Cleaning delicate machinery D. Cooking food © Boardworks Ltd 2003