Compare sound amplitude loudness frequency and pitch
Read time traces while changing one property at a time and distinguish graph amplitude from peak-to-peak height.
Section 3.4 · Sound
Exam scope and assessment notes
Core and Extended · Physics 0972, 2026–2028. Follow the selected spectrum or sound section. Diagrams illustrate stated ideal models and supplied data. Written practice is self-checked. Human subject-teacher review, supervised practical competence and cumulative assessment remain pending. Cambridge states that IGCSE 0972 has the same subject content as IGCSE 0625, with 9–1 grading. This StudyForA pathway maps the 2026–2028 syllabus only. This 9–1 graded qualification is available only in a limited number of administrative zones. Confirm that your centre can enter you for this code and exam series with Cambridge International. Cambridge has published a separate syllabus for 2029. StudyForA has not reconciled that version yet; this page supports exams in 2026, 2027 and 2028 only.
Before you begin
- Read an oscillation time trace.
- Distinguish amplitude from a complete-cycle count.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
A trace spans −2 to +2 units about zero. What is its amplitude?
What you will learn
- Relate amplitude to loudness under matched conditions.
- Relate frequency to pitch and read each property separately.
Change amplitude without changing frequency
A greater sound-wave amplitude generally corresponds to a louder sound at the same receiving conditions. Amplitude is the maximum magnitude from equilibrium or the reference value, not the full peak-to-peak span. A trace ranging from −2 to +2 units has amplitude 2 units and peak-to-peak span 4 units.
Comparisons should use the same source–receiver geometry, medium and measurement settings. Moving closer or changing microphone gain can increase a recorded amplitude without changing the emitted source frequency. Perceived loudness also depends on the listener and frequency; the school comparison holds those conditions suitably matched.
Count repetitions to compare pitch
Higher frequency corresponds to higher pitch within the audible range. A trace with four complete cycles in 0.010 s has frequency 400 Hz. A trace with eight in the same interval is 800 Hz, a higher pitch even if its displacement amplitude is unchanged.
A graph can change amplitude and frequency independently. Compare vertical excursion for amplitude and repeats per same time interval for frequency. A loud bass sound can have greater amplitude but lower frequency than a quiet high-pitched sound.
Pause and explain
Which change raises pitch without changing the stated amplitude?
Worked example
Trace A has amplitude 2 units and four cycles in 0.010 s. B has amplitude 1 unit and eight cycles in that time. Compare under matched conditions.
Show the worked solution
- A has greater amplitude and is generally louder.
- A has 400 Hz; B has 800 Hz.
- B has the higher pitch despite smaller amplitude.
Answer A is generally louder; B is higher pitched under the stated comparison.
Try a topic test
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Test this topic →From guided practice to a new situation
Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
A sound trace's amplitude doubles while frequency remains fixed. State the expected loudness and pitch changes under matched conditions.
Give me a hint
Treat the two properties separately.
Compare my reasoning
- Amplitude becomes greater.
- The sound is generally louder.
- Frequency is unchanged, so pitch is unchanged.
Generally louder; unchanged pitch.
Look for these in your work
- State both properties.
- Retain matched conditions.
A trace contains six complete cycles in 0.015 s. Calculate frequency.
Give me a hint
Count cycles per second rather than vertical height.
Compare my reasoning
- Count = 6 and time = 0.015 s.
- f = 6/0.015.
- f = 400 Hz.
400 Hz.
Look for these in your work
- Use complete cycles.
- State hertz.
A closer microphone records a larger amplitude with the same cycle rate. Must the source pitch have risen?
Give me a hint
Compare arrival amplitude and temporal repetition separately.
Compare my reasoning
- Receiver position can change amplitude.
- The measured cycle rate remains unchanged.
- No pitch increase follows from the amplitude change.
No; the unchanged frequency indicates unchanged pitch in this model.
Look for these in your work
- Identify the changed receiver condition.
- Do not infer frequency from amplitude.
Common mistakes
- Amplitude is half the peak-to-peak span.
- Louder does not mean higher pitch.
- Use the same time interval and receiver conditions.
What can you explain now?
Does doubling amplitude alone double frequency?
Compare with the explanation
No.
Amplitude and temporal repetition rate are independent properties in the model.
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Make it stick
Read amplitude and frequency separately, explain loudness and pitch, and state the comparison conditions.
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.