Chapter Objectives and Summaries
for the Oxford University Press text by Walding, Rapkins and Rossiter:-
" NEW CENTURY Senior Physics - Concepts in Context "
CHAPTER 16 Sound, music and audio technology.
Knowledge of subject matter
- Describe different ways of producing sound.
- Explain how sound travels through a medium as a longitudinal wave.
- Give examples of vibating objects that produce sound.
- Calculate the speed of sound at different temperatures.
- Describe an experiment to show that sound cannot ravel through a vacuum.
- Describe the reflection, refraction, diffraction and interference of sound.
- Explain the cause of echoes.
- Use the terms 'frequency', 'pitch', 'loudness' and 'quality' to describe different sounds.
- Describe a simple method for estimating the speed of sound. Indicate the speed of sound in different media.
- Describe the factors affecting the frequency of the note emitted by a vibrating string or air column.
- State the meaning of the terms: free and forces vibrations, resonance,fundamental, harmonic, overtone, end correction, beats, beat frequency.
- Distinguish between a closed and open pipe.
- Explain how microphones and loudspeakers work in terms of wave motion.
- Determine the frequency of sound from an oscilloscope trace.
- Explain the Doppler Effect and how a siren works.
- Distinguish between consonance and dissonance. Explain the musical scale.
- Discuss the intensity of sound and the decibel scale. Indicate the intensity in decibels of common sounds.
- Quantify, interpret and discuss the problem of noise pollution.
- Explain how different types of hi–fi equipment work. Distinguish between mono and stereo systems.
- Interpret and discuss factors that affect the acoustics of a room.
- Discuss examples of sound technology.
- Discuss the importance of recording and reproducing sound in our daily lives. Name devices used to record and reproduce sound.
- Interpret the sonic spectrum.
COMPLEX REASONING PROCESSES
- Solve complex problems on acoustics, strings and pipes.
CHAPTER 16 SUMMARY
- Sound is a form of energy produced by vibrating objects.
- Sound travels by means of longitudinal mechanical waves that require a medium for propagation.
- Human ears can detect sound between 20 Hz and 20 000 Hz but the higher level decreases with age.
- Sound waves can be reflected, refracted, diffracted and interfere.
- The pitch of a sound refers to the frequency of the sound. High pitch is the same as high frequency.
- The loudness of a sound refers to the amplitude of the wave or the energy carried by the wave.
- The quality of sounds refers to the mixture of frequencies produced by a musical instrument. The resultant waveform produced is made up of the fundamental frequency and a number of harmonics.
- Ultrasound are sounds that have frequencies above human hearing range.
- Ultrasound has many uses especially in medicine, sonar and by many animals.
- Musical sounds are produced by standing waves being set-up in musical instruments. The frequency of sound produced depends on the standing wave patterns.
- The frequency of sound waves produced by strings depends on the tension of the string, the length of the string and the mass per unit length of the string. The frequency produced in a string is expressed by the mathematical formula:
f = 1/2.L .(T/M)½
Where: f is the is the frequency of the note produced in Hz,
L is the length of the string in metres,
T is the tension in the string in newtons, and
M is the mass per unit length in kg m-1.
- Resonance is the effect that occurs when a body vibrates at its natural frequency.
- Beats are produced when two slightly different frequencies of sound occur at the same time. The difference between the two frequencies determines the beat frequency.
- The absolute intensity of sound is a measure of the sound energy carried by waves per second through an area of one metre square. It is measured in watts per square metre ( W m-2). The relative intensity level (b) is a measure of relative intensity compared to a reference level. It is measured in decibels (dB).
b = 10 log (I/Io). Where I is the intensity of the sound in W m-2, and Io is taken as the threshold of hearing (10-12 W m-2).
- Modern sound technology employs the use of microphones, amplifiers, loud speakers.
- Hi-Fi equipment usually consists of tuners, amplifiers, record players, CD players, and speaker systems.
- The Doppler effect is the change in frequency experienced when there is relative movement between the source and the receiver. The apparent frequency is given by the formula:
f1 = f.(v ±vo)/(v ±vs)
where:f1 is the apparent frequency
f is the frequency of waves produced by the stationary source,
v is the velocity of the waves,
vs is the velocity of the waves,
and vo is the velocity of the object.
- Sonic booms occur when planes break the sound barrier.
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