SOUND Self-Learning Package Click to proceed

Learning Objectives (a) describe the production of sound by vibrating sources (b) describe the longitudinal nature of sound waves in terms of the processes of compression and rarefaction (c) explain that a medium is required in order to transmit sound waves and the speed of sound differs in air, liquids and solids (d) describe a direct method for the determination of the speed of sound in air and make the necessary calculation (e) relate loudness of a sound wave to its amplitude and pitch to its frequency (f) describe how the reflection of sound may produce an echo, and how this may be used for measuring distances (g) define ultrasound and describe one use of ultrasound, e.g. quality control and pre-natal scanning

Previously in Waves... O You have learned that O A wave is a disturbance which transfers energy from one place to another without the transfer of matter O A longitudinal wave is a wave where the wave direction is parallel to the direction of vibrations O The frequency of a wave is the number of complete waves produced per second O The wavelength of a wave is the shortest possible distance between any two points in phase O The wave speed is the distance travelled by the wave per second O Wave speed = frequency x wavelength or v = f λ

In this lesson… O You will learn about a specific example of longitudinal waves: sound waves O You will also learn about the properties and applications of sound waves

How are Sound Waves formed? O Like all other waves, sound waves require a vibrating source O In a guitar or violin, the vibrating source are strings. In a drum or loudspeaker, the vibrating source is a thin membrane. O [For own research] What is the vibrating source for a flute?

Properties of Sound O Since sound is a longitudinal wave, it has compressions and rarefactions O In most cases, sound is travelling through air. In such cases, it is the air molecules which are vibrating, and air molecules form compressions and rarefactions O Air Pressure is highest at a compression, and lowest at a rarefaction (see Marshall Cavendish textbook pg 288 for diagram)

Properties of Sound O Sound cannot travel through vacuum, because there are no particles to vibrate O The link below shows an experiment of a ringing bell inside a bell jar. Air is first pumped out of the bell jar (creating a vacuum) and then allowed back into the bell jar. q0Gw q0Gw

Properties of Sound O Even though a sound wave is a longitudinal wave, it may be picked up by a microphone and converted into electrical signals O These electrical signals can then be converted into a transverse wave in an oscilloscope (see link below) O xI_GA xI_GA

Properties of Sound O The speed of sound in air is approximately 300 ms -1. O You are required to be able to describe an experiment to measure the speed of sound. Refer to Marshall Cavendish textbook pg 292 Investigation 15.1 O Sound may also pass through liquids and solids, but the speed of sound is not the same for each. O Sound travels fastest in solids and slowest in air.

Properties of Sound O The amplitude of a sound wave relates to the loudness of the sound O A loud sound has higher amplitude, a soft sound has lower amplitude O The frequency of a sound wave relates to the pitch of the sound O A high pitched sound has high frequency, a low pitched sound has low frequency

Echoes O Sound waves can get reflected upon hitting a surface O These reflections are called echoes O Echoes may be used to measure distances. This is the concept behind sonar (see Marshall Cavendish textbook pg 294 Worked Example 15.2)

Ultrasound O Ultrasound is sound with frequencies above the upper limit of human range of audibility (need to memorize definition) O In other words, ultrasound is sound waves with frequency so high they cannot be detected by the human ear. O They are used in quality control and pre- natal scanning (see Marshall Cavendish textbook pg 297)

Summary O Sound Waves are longitudinal waves with compressions and rarefactions O A medium (air, liquid or solid) is required for sound waves to pass through O Loudness is related to amplitude; pitch is related to frequency O Echoes are reflections of sound waves O Quality control and pre-natal scanning are applications of ultrasound

Assignment O Click on the link below to do your holiday assignment for the topic of SOUND O /forms/d/1bz_dC19Nr17dWJEinKE7Rm0hj 1AEwz7eTJSpaUDEK5M/viewform?usp=sen d_form /forms/d/1bz_dC19Nr17dWJEinKE7Rm0hj 1AEwz7eTJSpaUDEK5M/viewform?usp=sen d_form O Deadline: 31 Dec :59pm. Marks will be deducted for late submission. O Please note that you also need to complete your assignment for the other topic: ELECTROMAGNETIC SPECTRUM

THANK YOU [Press ‘Esc’ to exit] Please complete the learning package for ELECTROMAGNETIC SPECTRUM if you have not already done so