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14.0Sound

Overview: Sound: Properties, Detection and the Physics of Music — American System Physics Revision Notes & Topical Questions

5 min read 7 parts Lesson 2 of 5 Unit quiz

📚 American System Physics Hub / Topical Revision
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Lesson summary

Describe properties of sound.Sound cannot travel through a vacuum.Sound travels faster in solids than gases.A 10 dB increase is ten times the intensity.Timbre depends on the mix of harmonics.The human ear hears about 20 Hz to 20 000 Hz.Describe properties of sound.Explain the Dop…

  • A tube closed at one end is 0.25 m long. Fundamental frequency (v = 340 m/s)?
  • Two tuning forks: 440 Hz and 444 Hz. Beat frequency?
  • Sound wave
  • Doppler effect
  • Identify / Describe (FRQ)
  • Explain / Justify (FRQ)

Section 1 of 7Overview: Sound: Properties, Detection and the Physics of Music

14.1 Sound: Properties, Detection and the… concept map: Strings, A tube closed at one end is 0, Two tuning forks: 440 Hz and, Sound wave, Pitch
Visual guide to the key ideas explained in this lesson.
Ultrasound (> 20 kHz) is used in medical imaging.
Echolocation uses reflected sound.
Sonic booms occur when a source exceeds the speed of sound.
Strings
Strings fn = nv/2L.
Tuning uses beats to match frequencies.

Section 2 of 7Process & sequence

1
Identify the source frequency.
2
For Doppler: approaching raises observed frequency, receding lowers it.
3
For pipes, match length to allowed wavelengths.
4
Find frequency from f = v/λ.
5
For beats, subtract the two frequencies.

Doppler effectwrite these steps in this order; each step is a marking point.

1
Source emits waves
2
Source moves
3
Waves bunch ahead
4
Higher pitch ahead
5
Lower pitch behind

Section 3 of 7Compare

Speed of sound
MediumApprox. speed (m/s)
Air (20 °C)343
Water1500
Steel5900
Resonant pipes
PipeResonant lengthsHarmonics present
Closed at one endλ/4, 3λ/4, 5λ/4Odd only
Open both endsλ/2, λ, 3λ/2All
Decibel scale
SounddB
Whisper20
Conversation60
Rock concert110
Pain threshold120

Section 4 of 7Worked examples

1A tube closed at one end is 0.25 m long. Fundamental frequency (v = 340 m/s)?
  • λ = 4L = 1.0 m; f = 340 Hz.
2Two tuning forks
440 Hz and 444 Hz. Beat frequency?
  • 4 Hz.

Section 5 of 7Key terms

Section 6 of 7Command terms

Command terms
Identify / Describe (FRQ)
A short, specific statement; describing requires relevant characteristics, not a single word.
Explain / Justify (FRQ)
Give the cause-and-effect reasoning or evidence; a restated fact does not score.
Calculate
Show setup, substitution and the answer with units.
Predict
State the expected outcome; add a reason only if asked to justify.
MCQ technique
Read every option; eliminate distractors that are true statements but do not answer the question; watch for NOT/EXCEPT.

Section 7 of 7Exam technique

Keywords the mark scheme looks for in this lesson

Keywords the mark scheme looks for in this lesson
Sound wave · Pitch · Loudness · Doppler effect · Resonance · Fundamental · Harmonics · Beats
Learn each definition in the Key words tab exactly; a missing keyword in a definition usually loses the mark.

How to get full marks (examiner guidance)

1
Answer exactly what is asked; extra correct material does not earn credit, and contradictory statements can cancel credit (AP FRQ).
2
Use precise vocabulary (e.g. “active site”, “concentration gradient”, “allele”), never “it/stuff/things”.
3
Show units and working in calculations.
4
In MCQs, predict the answer before reading the options, then eliminate.

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