SOUNDSelf-Learning Package

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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 = fλ

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 SoundO Since sound is a longitudinal wave, it

has compressions and rarefactionsO 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 SoundO 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. http://www.youtube.com/watch?v=ce7AMJdq0Gw

Properties of SoundO 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 http://www.youtube.com/watch?v=0uNHMsxI_GA

Properties of SoundO 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 SoundO The amplitude of a sound wave

relates to the loudness of the soundO A loud sound has higher amplitude, a

soft sound has lower amplitudeO The frequency of a sound wave

relates to the pitch of the soundO A high pitched sound has high

frequency, a low pitched sound has low frequency

EchoesO Sound waves can get reflected upon

hitting a surfaceO These reflections are called echoesO Echoes may be used to measure

distances. This is the concept behind sonar (see Marshall Cavendish textbook pg 294 Worked Example 15.2)

UltrasoundO 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)

SummaryO Sound Waves are longitudinal waves

with compressions and rarefactionsO 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 wavesO Quality control and pre-natal scanning

are applications of ultrasound

AssignmentO Click on the link below to do your

holiday assignment for the topic of SOUND

O https://docs.google.com/a/preshigh.edu.sg/forms/d/1bz_dC19Nr17dWJEinKE7Rm0hj1AEwz7eTJSpaUDEK5M/viewform?usp=send_form

O Deadline: 31 Dec 2014 11:59pm. 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

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