Wave II (Sound) Teacher Version.pdf

CHAPTER 12 (Part 2) Sound Chapter 11 Sound 11.1 What is Sound? 11.2 Transmission of Sound 11.3 Reflection of Sound 11.4 Ultrasound 11.5 Pitch and Loudness 11.1 What is Sound? Learning Outcomes At the end of this section, you should be able to: describe how sound is ge...

CHAPTER 12 (Part 2) Sound Chapter 11 Sound 11.1 What is Sound? 11.2 Transmission of Sound 11.3 Reflection of Sound 11.4 Ultrasound 11.5 Pitch and Loudness 11.1 What is Sound? Learning Outcomes At the end of this section, you should be able to: describe how sound is generated by vibration; describe the mechanism by which sound travels. 11.1 What is Sound? Sound is a form of energy that is transferred from one point to another as a longitudinal wave. How is Sound Produced? How does a guitar produce sound? Click here for sound generator UR L Click here for sound generation in water 11.1 What is Sound? How is Sound Produced? Sound is a produced by vibrating sources placed in a medium. How does a Sound Wave Propagate? If a vibrating tuning fork is dipped into a glass of water, the water in the glass will splash out. This is because the water is displaced by the vibrating tuning fork. 11.1 What is Sound? How does a Sound Wave Propagate? The vibrating tuning fork displaces the molecules of the medium around it, which in turn displaces their neighbouring molecules. We have learnt in earlier part of the chapter that sound waves are longitudinal waves. This means that the direction of vibration of the medium’s molecules is parallel to the direction the wave travels. direction of wave motion direction of particle vibration 11.1 What is Sound? Click here for simulation of sound wave How does a Sound Wave Propagate? All longitudinal waves propagate as a series of compressions (C) and rarefactions (R). Compressions are regions where the medium’s density is higher than the surrounding density. Rarefactions are regions where the medium’s density is lower than the surrounding density. 11.1 What is Sound? How does a Sound Wave Propagate? 1 Layers of air are in undisturbed positions. 2 When the prongs push outwards, a region of compression is produced. 3 When the prongs move inwards, a region of rarefaction is produced. 4 ,5 The prongs continue to vibrate (move inward and outward) and a series of compressions and rarefactions is set up. How does sound propagate? Vibrating source disturbs the neighbouring molecules causing it to vibrate. The direction of vibration is parallel to the direction of sound wave A series of compression and rarefaction is formed This transfers energy from vibrating source to the target without a transfer of the medium / matter 11.1 What is Sound? Graphs of Sound Waves Pressure–distance graph 11.1 What is Sound? Graphs of Sound Waves 1 1 2 2 1 The amplitude A of a 2 The wavelength λ of the sound sound wave is the wave is the distance between maximum pressure the centres of two consecutive change. compressions or rarefactions. 11.1 What is Sound? Graphs of Sound Waves Displacement–distance graph  11.1 What is Sound? Graphs of Sound Waves Displacement Distance Compare the compression displacement–distance and pressure–distance Pressure rarefaction graphs of a sound wave. Surrounding air pressure Distance 11.1 What is Sound? Graphs of Sound Waves Displacement–time graph Chapter 11 Sound 11.1 What is Sound? 11.2 Transmission of Sound 11.3 Reflection of Sound 11.4 Ultrasound 11.5 Pitch and Loudness 11.2 Transmission of Sound Learning Outcomes At the end of this section, you should be able to: explain that sound needs a medium for transmission; explain that the speed of sound differs in solids, liquids and gases; describe a method for determining the speed of sound in air. 11.2 Transmission of Sound Can Sound be Transmitted Through a Vacuum? The electric bell is switched on and the air in the jar is slowly pumped out to create a vacuum. What do you think will be observed as the air is pumped out? 11.2 Transmission of Sound Can Sound be Transmitted Through a Vacuum? When the electric bell is on and the vacuum pump is off, you will hear the bell. When the vacuum pump is switched on, the sound of the bell becomes softer and softer until you can no longer hear it. Sound cannot travel through a vacuum. It needs a medium to travel from one point to another. 11.2 Transmission of Sound Medium of Transmission Sound needs a medium to travel from one point to another. It travels at different speeds in different media. Medium Air Water Iron Granite Approximate speed 300 1500 5000 5400 of sound/m s–1 Speed of sound < Speed of sound < Speed of sound in gas in liquid in solid AZ: Good to know but not tested! Click here for speed of sound in different medium Chapter 11 Sound 11.1 What is Sound? 11.2 Transmission of Sound 11.3 Reflection of Sound 11.4 Ultrasound 11.5 Pitch and Loudness 11.3 Reflection of Sound Learning Outcomes At the end of this section, you should be able to: explain how an echo is formed; describe the use of echoes in measuring distances. 11.3 Reflection of Sound Why do you hear echoes when you shout in an empty room? 11.3 Reflection of Sound How are Echoes Formed? An echo is formed when a sound is reflected off a hard, flat surface such as a large wall. An echo is the repetition of a sound due to the reflection of sound. AZ: What is the difference between echo and reverberation? 11.3 Reflection of Sound Echoes obey the laws of reflection. The angle of incidence i is equal to the angle of reflection r.  11.3 Reflection of Sound Uses of Echoes The depth of the sea can be measured using echoes. How? Speed of 2 × depth of sea sound in sea = time taken Click here for video on simulation of echolocation The ship sends out a pulse of sound (a signal). By noting the time taken for the sound to be reflected back to the ship, and with knowledge of the speed of sound in the sea, we can calculate the depth of the sea. 11.3 Reflection of Sound Uses of Echoes Echoes can be used to measure large distances (like the depth of the sea); detect the location of objects (i.e. echolocation). Echolocation used to detect the location of fish Chapter 11 Sound 11.1 What is Sound? 11.2 Transmission of Sound 11.3 Reflection of Sound 11.4 Ultrasound 11.5 Pitch and Loudness 11.4 Ultrasound Learning Outcomes At the end of this section, you should be able to: state what ultrasound is; describe how ultrasound is used in quality control and prenatal scanning. 11.4 Ultrasound What Sounds are Audible? The human ear is capable of detecting sounds in a certain range of frequencies. This range of frequencies is called the range of audibility. For humans, this range is from 20 Hz (lower limit) to 20 000 Hz (upper limit). 11.4 Ultrasound Spectrum of Sound Frequencies Humans cannot hear low frequency sounds (infrasound) and high frequency sounds (ultrasound). Ultrasound is sound with frequencies above the upper limit of the human range of audibility. 11.4 Ultrasound Uses of Ultrasound Quality control Ultrasound can be used to check for cracks and cavities in concrete slabs and metal pipes. 1 Transmitter emits ultrasound 2 Ultrasound passes through the concrete and is received by a sensor. 3 The presence and location of defects are identified by comparing the ultrasound emitted with the ultrasound received. 11.4 Ultrasound Uses of Ultrasound Prenatal scanning Ultrasound can be to obtain images of structures in the body. It is used, instead of X-rays, to examine the development of foetuses because it does not harm the foetus. Chapter 11 Sound 11.1 What is Sound? 11.2 Transmission of Sound 11.3 Reflection of Sound 11.4 Ultrasound 11.5 Pitch and Loudness 11.5 Pitch and Loudness Learning Outcome At the end of this section, you should be able to: relate the loudness and pitch of a sound to the amplitude and frequency of the sound wave respectively.  11.5 Pitch and Loudness Click here for sound generator Pitch Click here for video on pitch vs loudness Pitch is related to the frequency of a sound wave. The higher the frequency, the higher the pitch. Recall that the frequency of a wave is the number of complete waves produced per second. Question Which sound has the lower pitch — sound A or sound B? Sound A Sound B 11.5 Pitch and Loudness Loudness Loudness is related to the amplitude of a sound wave. The larger the amplitude, the louder the sound. Recall that the amplitude of a wave is the maximum displacement of a point from its rest position. Question Which sound is louder — sound A or sound B? Sound A Sound B  Chapter 11 Sound Sound production transmission echoes Produced by a Transfers energy Can be properties vibrating source from one point to reflected off a another via a hard surface series of Longitudinal wave compressions Pitch an loudness Applications and rarefactions frequency – Pitch is related to the Measure large range frequency of the distances sound wave. Requires a Detect location – Loudness is related medium for of objects to the amplitude of propagation the sound wave. 20 Hz – 20 kHz >20 kHz The speed of propagation Human audible Ultrasound depends on the medium: range used in quality Vgas < vliquid < vsolid control and prenatal scanning