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© Boardworks Ltd 2003 A slide contains teacher’s notes wherever this icon is displayed - To access these notes go to ‘Notes Page View’ (PowerPoint 97)

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Presentation on theme: "© Boardworks Ltd 2003 A slide contains teacher’s notes wherever this icon is displayed - To access these notes go to ‘Notes Page View’ (PowerPoint 97)"— Presentation transcript:

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2 © Boardworks Ltd 2003

3 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). Normal ViewNotes Page View Teacher’s Notes Flash Files A flash file has been embedded into the PowerPoint slide wherever this icon is displayed – These files are not editable.

4 © 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.

5 © Boardworks Ltd 2003 Music What vibrates when you sing? Your voice-box. What vibrates when you play a violin? The strings

6 © Boardworks Ltd 2003 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. The Bell-jar experiment What happens when the air is removed from the bell-jar?

7 © Boardworks Ltd 2003 Sound : How fast does it travel? You need a quiet open space at least 100m long to perform this investigation. > 100m START STOP 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:

8 © Boardworks Ltd 2003  Calculate your average speed of sound : Av. = [try 1 + try 2 + try 3 + try 4]  4.  What errors could have crept into your results? Sound : How fast does it travel?

9 © Boardworks Ltd 2003 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] Sound : How fast does it travel?

10 © Boardworks Ltd 2003 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: solidliquidgas In which state are the particles closest together? In which state are the particles furthest apart? solid gas Which state does sound travel fastest through? Why? 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.

11 © 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.

12 © 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

13 © 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

14 © Boardworks Ltd 2003 Reflection : Echoes Stand at least 100m from a large, straight wall 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  Remember, this is ‘two way travel time’ [twtt] STARTSTOP 150m

15 © Boardworks Ltd 2003  The sound takes 0.92s to travel 300m Remember the formula for speed? SPEED = DISTANCE  TIME v = 300  0.92 v = 326 m/s For the Higher Tier paper you will need to be able to change the subject of the formula Repeat this several times to obtain an average Reflection : Echoes

16 © Boardworks Ltd 2003 Reflection : questions Which of these travel faster than the speed of sound in air?

17 © Boardworks Ltd 2003 Studying sound Signal generators can produce signals over a range of frequencies and of varying amplitudes. Loudspeakers convert the signal from the signal generator into sound waves. The oscilloscope allows us to study the frequency and loudness of a sound.

18 © 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.

19 © Boardworks Ltd 2003 Oscilloscope traces Which trace represents the highest pitched sound? AB ‘A’ is the highest pitched sound because it has the shortest wavelength/most number of waves visible.

20 © Boardworks Ltd 2003 Loudness A quiet sound. A louder 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.

21 © Boardworks Ltd 2003 Which trace represents the loudest sound? AB ‘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. Oscilloscope traces

22 © Boardworks Ltd 2003 Wave animation

23 © 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.  The lowest frequency I can hear is ________ Hz  The highest frequency I can hear is ________ Hz

24 © 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. This changes with age. A baby has a wider range than an older person.  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.

25 © Boardworks Ltd 2003 Sound : Are we all the same?  Hearing is tested using an audiometer and the results are shown on an audiogram. Hearing Loss [dB]

26 © Boardworks Ltd 2003 Sound : Hearing Ranges Animal Which animal can hear the lowest frequency? pigeons Which animal can hear the highest frequency? moths

27 © Boardworks Ltd 2003 Sound : The ear 1. Sound waves are collected by the ear lobe or pinna. 2. The waves travel along the ear canal. 3. The waves make the ear drum vibrate. 4. The small bones [ossicles] amplify the vibrations. 5. The cochlea turns the vibrations into electrical signals. 6. The auditory nerve takes the signals to the brain.

28 © Boardworks Ltd 2003 Sound : The ear 1.Sound waves are collected by the ear lobe or pinna. 2.The waves travel along the ear canal. 3.The waves make the ear drum vibrate. 4.The small bones (ossicles) amplify the vibrations. 5.The cochlea turns these into electrical signals. 6.The auditory nerve takes the signals to the brain

29 © Boardworks Ltd 2003 Sound : The ear

30 © Boardworks Ltd 2003 Sound : How loud are sounds? Permanent ear damage Can just be heard Aircraft overhead Personal stereo A circular saw at 2m Loud bell Pin being dropped Quiet countryside

31 © Boardworks Ltd 2003 What is noise? A noise is any unwanted sound. What you might not consider noise, loud music for example, other people might. What are the effects of noise? 1._________ 2._________ 3._________ 4._________ Nausea Vomiting Headaches Deafness How can you reduce the effects of loud noise? 1._________________ 2._________________ 3.___________________ _______________ Ear protectors Putting noisy machinery in insulated rooms Double glazing

32 © Boardworks Ltd 2003 What is the upper range of human hearing? A.20 Hz B.200 Hz C Hz D Hz

33 © Boardworks Ltd 2003 What causes all sounds? A.Vibrations B.Reflections C.Refractions D.Heat

34 © Boardworks Ltd 2003 Which of the following can sound not travel through? A.Liquid B.Vacuum C.Solid D.Gas

35 © 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

36 © 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


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