Klank - Graad 10 [CAPS]
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Module by: Luca Lategan, Free High School Science Texts Project. E-mail the authorsEdited By:
Luca Lategan, Free High School Science Texts ProjectTranslated By:
Luca Lategan, Free High School Science Texts Project
Based on: Sound - Grade 10 (11) [CAPS] by Rory Adams, Free High School Science Texts Project, Mark Horner, Heather Williams Inleiding
Nou dat ons die basiese beginsels van longitudinale golwe bespreek het, is ons gereed om klankgolwe meer volledig te bestudeer.
Het jy al ooit gewonder oor hoe ongelooflik jou gehoor is? Dit is eintlik heel merkwaardig. In jou omgewing is daar baie verskillende tipes klank: toeters, ’n laggende baba, ’n blaffende hond en tog kan jou brein hulle almal op een of ander manier verwerk. Alhoewel al hierdie dinge vir jou ingewikkeld mag klink, word dit eintlik nogal eenvoudig sodra jy ’n baie maklike feit geleer het. Klank is bloot ’n golf, daarom kan jy alles wat jy van golwe af weet gebruik om klank te verstaan.
Eienskappe van ’n Klankgolf
Aangesien klank ’n golf is, kan ons die eienskappe van klank in verband bring met dié van golwe. Die basiese eienskappe van klank is: toonhoogte, hardheid en toon. Figuur 1: Toonhoogte en hardheid van klank. Klank B het 'n laer toonhoogte (laer frekwensie) as klank A en is sagter (kleiner amplitude) as klank C.
(a) (b) (c) Toonhoogte
Die frekwensie van 'n klankgolf is wat jou oor as toonhoogte verstaan. 'n Hoër frekwensie klank het 'n hoër toonhoogte en 'n laer frekwensie klank het 'n laer toonhoogte. In figuur 1 het klank A 'n hoër toonhoogte as klank B. Byvoorbeeld: die skril gekwetter van 'n voëltjie sal 'n hoë toonhoogte hê, maar die diep gebrul van 'n leeu sal 'n lae toonhoogte hê.
Jou oor kan 'n wye reeks frekwensies bespeur (optel). Frekwensies van 20 tot 20 000 Hz is hoorbaar deur die menslike oor. Enige klank met 'n frekwensie onder 20 Hz staan bekend as 'n infraklank en enige klank met 'n frekwensie bo 20 000 Hz word 'n ultraklank genoem.
tabel 1 gee 'n aanduiding van die gehoorbestek van party diere in vergelyking met die mens.
Tabel 1: Omvang van frekwensies
onderste frekwensie (Hz)
boonste frekwensie (Hz)
Ondersoek: Bestek van Golflengtes
Deur van die inligting in tabel 1 gebruik te maak, bepaal die onder- en bogrense van golflengtes wat elke spesie kan hoor. Neem aan dat die spoed van klank in lug 344 m s-1-1 is.
Die amplitude van ’n klankgolf word bepaal deur sy hardheid of volume. ’n Groter amplitude beteken ’n harder klank en ’n kleiner amplitude beteken weer ’n sagter klank. In figuur 1 is klank C harder as klank B. Die vibrasie van ’n bron bepaal die amplitude van die golf. Bronne stuur energie deur die medium met behulp van vibrasies. Meer energieke vibrasies lei tot groter amplitudes. Hoe groter die amplitude, hoe groter is die agressie waarmee die molekules heen-en-weer beweeg.
Daar is ook ander fasette wat die hardheid van ’n klank beïnvloed. Een van hulle is die sensitiwiteit van die oor. Die menslike oor is meer sensitief vir sommige frekwensies as ander. Die volume wat ons waarneem hang dus van beide die amplitude van ’n klankgolf én of die frekwensie in die omvang lê waar die oor min-of-meer sensitief is.
Toonhoogte is ’n maatstaf van die kwaliteit van ’n klankgolf. Byvoorbeeld: die kwaliteit van die klank wat in ’n spesifieke musikale instrument gelewer word hang af van watter harmoniese tone daarop gesuperponeer (geplaas) is en in watter verhoudings. Harmoniese tone verwys na klankgolwe wat in ooreenstemming met mekaar is en word bepaal deur die staande golwe wat in die instrument geproduseer word. Hoofstuk (Verwysing) sal die fisika agter musiek in groter besonderhede bespreek.
Die gehalte (timbre of klanktint) van ’n gehoorde klank is afhanklik van die patroon van die inkomende vibrasies, dus, die vorm van die klankgolf. Wanneer die vibrasies meer onreëlmatig is, sal die vorm van die klankgolf ru wees en sal die klank wat gehoor word ook growwer klink.
Die spoed van klank is afhanklik van die medium waarin dit beweeg. Klank beweeg vinniger in vastestowwe as in vloeistowwe en vinniger in vloeistowwe as in gasse. Hierdie verskynsel is danksy die feit dat die digtheid van vastestowwe hoër is as dié van vloeistowwe wat beteken dat die deeltjies nader aan mekaar is en die geluid makliker oorgedra kan word.
’n Ander faktor wat die spoed beïnvloed is die temperatuur van die medium. Hoe warmer die medium is, hoe vinniger beweeg die deeltjies en dus sal die klank ook vinniger deur die medium beweeg. Wanneer ons ’n stof verhit, het die deeltjies in daardie stof meer kinetiese energie en sal dit vibreer of vinniger beweeg. Daarom kan klank vinniger en makliker deur warm stowwe gelei word.
Klankgolwe is drukgolwe. Die spoed van klank sal dus deur die druk van die medium waardeur dit gaan beïnvloed word. By seevlak is die lugdruk hoër as hoog bo-op ’n berg. Klank sal vinniger by seevlak beweeg, waar die druk hoog is, as by plekke hoog bo seespieël.
Definition 1: Spoed van klank
Die spoed van klank in lug, by seevlak, ’n temperatuur van 21∘∘C en onder normale atmosferiese omstandighede is 344m s-1-1.
Klank frekwensie en amplitude
Bestudeer die volgende diagram wat ’n musieknoot voorstel. Teken nou in jou werkboek die kurwes wat elk van die volgende klanke voorstel:’n hoër toonhoogte harder sagterFiguur 2
Fisika van die oor en gehoor
Figuur 3: Diagram van die menslike oor.
Die menslike oor word in drie hoof afdelinge verdeel: die buite-, middel en binne-oor. Laat ons nou die reis volg wat ’n klankgolf neem vanaf die pinna (buitenste deel) na die gehoorsenuwee (diepste deel) wat seine na die brein deurstuur. Die pinna is die deel van die oor waaraan ons tipies dink wanneer ons na die oor verwys. Sy hoof funksie is om ’n invallende klankgolf te versamel en op die gehoorkanaal te fokus. Die klankgolf beweeg dan deur die gehoorkanaal tot dit by die oordrom uitkom. Skommelings in die druk van die klankgolf veroorsaak dat die oordrom vibreer. Daar is drie verskriklike klein beentjies in die middeloor, die hamer (malleus), aambeeld (inkus) en stiebeuel (stapes). Hierdie beentjies stuur die klanksein deur ’n ovaal venster wat die begin is van die binneoor. Vanaf hierdie ovaal venster word die klankgolwe oorsein deur die vloeistof in die binneoor en vertolk as klanke deur die brein. Die binne-oor, gemaak van die halfsirkelvormige kanale, die koglea en die gehoorsenuwee, is gevul met vloeistof. Hierdie vloeistof laat die liggaam toe om vinnige bewegings op te spoor en balans te behou. Die slak-vormige koglea is oortrek met meer as 25 000 haaragtige senuweeselle. Verskillende senuselle vibreer teen verskillende frekwensies. Wanneer ’n senusel vibreer, stuur dit elektriese impulse na die gehoorsenuwee. Hierdie impulse word na die brein gestuur deur die gehoorsenuwee en geïnterpreteer as klank.
Ultraklank is klank met ’n frekwensie van hoër as 20 kHz. Sommige diere, soos honde, dolfyne en vlermuise, het ’n bo-grens hoër as dié van die menslike oor en hul kan ultraklank hoor.
Die mees algemene gebruik van ultraklank is om beelde mee te skep wat industriële en mediese toepassings het. Die gebruik van ultraklank om beelde mee te skep is gebaseer op die refleksie en deurstuur van ’n golf by ’n grens. Soos ’n ultraklank golf binne ’n voorwerp beweeg wat uit verskillende materiale bestaan, soos die liggaam, sal grense bereik word, byvoorbeeld tussen been en spiere, spiere en vet, elke keer word ’n deel daarvan gereflekteer en ’n ander word deurgestuur. Gereflekteerde strale word bespeur en word gebruik om ’n beeld van die objek te skep.
Opmerking: Interesting Fact: Ultrasound generator/speaker systems are sold with claims that they frighten away rodents and insects, but there is no scientific evidence that the devices work; controlled tests have shown that rodents quickly learn that the speakers are harmless.
Ships on the ocean make use of the reflecting properties of sound waves to determine the depth of the ocean. A sound wave is transmitted and bounces off the seabed. Because the speed of sound is known and the time lapse between sending and receiving the sound can be measured, the distance from the ship to the bottom of the ocean can be determined, This is called sonar, which stands fromSoundNavigationAndRanging.
Exercise 1: SONAR
A ship sends a signal to the bottom of the ocean to determine the depth of the ocean. The speed of sound in sea water is 1450m.s-1m.s-1If the signal is received 1,5 seconds later, how deep is the ocean at that point?
Stap 1. Identify what is given and what is being asked:: s=1450m.s-1t=1,5sthereandback∴t=0,75sonewayd=?s=1450m.s-1t=1,5sthereandback∴t=0,75sonewayd=?(1) Stap 2. Calculate the distance:: Distance=speed×timed=s×t=1450m.s-1×0,75s=1087,5mDistance=speed×timed=s×t=1450m.s-1×0,75s=1087,5m(2)
belangrik: Advanced Section: This section is more advanced than required and is best revisited for interest only when you are comfortable with concepts like power and logarithms.
The unit of intensity is thedecibel(symbol: dB). This reduces to an SI equivalent ofW m-2W m-2.
The average threshold of hearing is10-12W m-210-12W m-2. Below this intensity, the sound is too soft for the ear to hear. The threshold of pain is1.0W m-21.0W m-2. Above this intensity a sound is so loud it becomes uncomfortable for the ear.
Notice that there is a factor of10121012between the thresholds of hearing and pain. This is one reason we define the decibel (dB) scale.
The intensity in dB of a sound of intensityII, is given by:
Tabel 2: Examples of sound intensities.
Notice that there are sounds which exceed the threshold of pain. Exposure to these sounds can cause immediate damage to hearing. In fact, exposure to sounds from 80 dB and above can damage hearing over time. Measures can be taken to avoid damage, such as wearing earplugs or ear muffs. Limiting exposure time and increasing distance between you and the source are also important steps for protecting your hearing.
Sound waves are longitudinal waves Thefrequencyof a sound is an indication of how high or low thepitchof the sound is. The human ear can hear frequencies from 20 to 20 000 Hz.Infrasoundwaves have frequencies lower than 20 Hz.Ultrasoundwaves have frequencies higher than 20 000 Hz. Theamplitudeof a sound determines itsloudnessor volume. Thetoneis a measure of thequalityof a sound wave. The speed of sound in air is around 340 m.s-1-1. It is dependent on the temperature, height above sea level and the phase of the medium through which it is travelling. Sound travels faster when the medium is hot. Sound travels faster in a solid than a liquid and faster in a liquid than in a gas. Sound travels faster at sea level where the air pressure is higher. The intensity of a sound is the energy transmitted over a certain area. Intensity is a measure of frequency. Ultrasound can be used to form pictures of things we cannot see, like unborn babies or tumors. Echolocation is used by animals such as dolphins and bats to “see” their surroundings by using ultrasound. Ships use sonar to determine how deep the ocean is or to locate shoals of fish.
Choose a word from column B that best describes the concept in column A.Tabel 3Column AColumn Bpitch of soundamplitudeloudness of soundfrequencyquality of soundspeed waveform A tuning fork, a violin string and a loudspeaker are producing sounds. This is because they are all in a state of:compression rarefaction rotation tension vibration What would a drummer do to make the sound of a drum give a note of lower pitch?hit the drum harder hit the drum less hard hit the drum near the edge loosen the drum skin tighten the drum skin What is the approximate range of audible frequencies for a healthy human?0.2 Hz→→200 Hz 2 Hz→→2 000 Hz 20 Hz→→20 000 Hz 200 Hz→→200 000 Hz 2 000 Hz→→2 000 000 Hz X and Y are different wave motions. In air, X travels much faster than Y but has a much shorter wavelength. Which types of wave motion could X and Y be?Tabel 4 XYAmicrowavesred lightBradioinfra redCred lightsoundDsoundultravioletEultravioletradio Astronauts are in a spaceship orbiting the moon. They see an explosion on the surface of the moon. Why can they not hear the explosion?explosions do not occur in space sound cannot travel through a vacuum sound is reflected away from the spaceship sound travels too quickly in space to affect the ear drum the spaceship would be moving at a supersonic speed A man stands between two cliffs as shown in the diagram and claps his hands once.Figuur 5Assuming that the velocity of sound is 330 m.s-1-1, what will be the time interval between the two loudest echoes?1616s 5656s 1313s 1 s 2323s A dolphin emits an ultrasonic wave with frequency of 0,15 MHz. The speed of the ultrasonic wave in water is 1 500 m.s-1-1. What is the wavelength of this wave in water?0.1 mm 1 cm 10 cm 10 m 100 m The amplitude and frequency of a sound wave are both increased. How are the loudness and pitch of the sound affected?Tabel 5 loudnesspitchAincreasedraisedBincreasedunchangedCincreasedloweredDdecreasedraisedEdecreasedlowered A jet fighter travels slower than the speed of sound. Its speed is said to be:Mach 1 supersonic isosonic hypersonic infrasonic A sound wave is different from a light wave in that a sound wave is:produced by a vibrating object and a light wave is not. not capable of travelling through a vacuum. not capable of diffracting and a light wave is. capable of existing with a variety of frequencies and a light wave has a single frequency. At the same temperature, sound waves have the fastest speed in:rock milk oxygen sand Two sound waves are traveling through a container of nitrogen gas. The first wave has a wavelength of 1,5 m, while the second wave has a wavelength of 4,5 m. The velocity of the second wave must be:1919the velocity of the first wave. 1313the velocity of the first wave. the same as the velocity of the first wave. three times larger than the velocity of the first wave. nine times larger than the velocity of the first wave. Sound travels at a speed of 340 m s-1-1. A straw is 0,25 m long. The standing wave set up in such a straw with one end closed has a wavelength of 1,0 m. The standing wave set up in such a straw with both ends open has a wavelength of 0,50 m.calculate the frequency of the sound created when you blow across the straw with the bottom end closed. calculate the frequency of the sound created when you blow across the straw with the bottom end open. A lightning storm creates both lightning and thunder. You see the lightning almost immediately since light travels at3×108m s-13×108m s-1. After seeing the lightning, you count 5 s and then you hear the thunder. Calculate the distance to the location of the storm. A person is yelling from a second story window to another person standing at the garden gate, 50 m away. If the speed of sound is 344 m s-1-1, how long does it take the sound to reach the person standing at the gate? A piece of equipment has a warning label on it that says, "Caution! This instrument produces 140 decibels." What safety precaution should you take before you turn on the instrument? What property of sound is a measure of the amount of energy carried by a sound wave? How is intensity related to loudness? Person 1 speaks to person 2. Explain how the sound is created by person 1 and how it is possible for person 2 to hear the conversation. Sound cannot travel in space. Discuss what other modes of communication astronauts can use when they are outside the space shuttle? An automatic focus camera uses an ultrasonic sound wave to focus on objects. The camera sends out sound waves which are reflected off distant objects and return to the camera. A sensor detects the time it takes for the waves to return and then determines the distance an object is from the camera. If a sound wave (speed = 344 m s-1-1) returns to the camera 0,150 s after leaving the camera, how far away is the object? Calculate the frequency (in Hz) and wavelength of the annoying sound made by a mosquito when it beats its wings at the average rate of 600 wing beats per second. Assume the speed of the sound waves is 344 m s-1-1. How does halving the frequency of a wave source affect the speed of the waves? Humans can detect frequencies as high as 20 000 Hz. Assuming the speed of sound in air is 344 m s-1-1, calculate the wavelength of the sound corresponding to the upper range of audible hearing. An elephant trumpets at 10 Hz. Assuming the speed of sound in air is 344 m s-1-1, calculate the wavelength of this infrasonic sound wave made by the elephant. A ship sends a signal out to determine the depth of the ocean. The signal returns 2,5 seconds later. If sound travels at 1450 m.s-1-1in sea water, how deep is the ocean at that point?
This work is licensed by Luca Lategan and Free High School Science Texts Project under a Creative Commons Attribution License (CC-BY 3.0), and is an Open Educational Resource. Last edited by Luca Lategan on May 8, 2011 3:19 pm -0500. Add to a lens