4PH1

Sound

Waves

Exam Frequency Analysis

Past paper frequency (2018 to 2024)

This topic accounts for approximately 7% of your exam marks.

stable
Low
Stable7%

Speed of sound calculations, echo timing and ultrasound uses are standard shorter questions.

Pitch is set by frequency

  • The of a sound is how high or low it sounds to the ear
  • Pitch is determined by the of the vibrating source:
    • A vibration at a high frequency produces a high-pitched (treble) sound
    • A vibration at a low frequency produces a low-pitched (bass) sound
  • On the oscilloscope: a higher pitch shows more wave cycles in the same horizontal width, and a shorter peak-to-peak distance
Two oscilloscope traces on the same time base: the higher-pitched (red) wave completes one cycle in 6 squares while the lower-pitched (blue) wave takes 12 squares, so the higher-frequency sound packs more cycles into the same width.
Source: Loudness and pitch by Save My Exams

Loudness is set by amplitude

  • The of a sound is how strong it sounds to the ear
  • Loudness is determined by the of the wave (the size of the back-and-forth movement of the air):
    • A larger amplitude produces a louder sound
    • A smaller amplitude produces a quieter sound
  • On the oscilloscope: a louder sound shows a taller wave from the centre line, while a quieter one has a shorter trace
Two oscilloscope traces at the same frequency: the louder (blue) wave rises 4 squares from the centre line while the quieter (green) wave rises only 2 squares, showing that a larger amplitude means a louder sound.
Source: Loudness and pitch by Save My Exams

Independence

  • Pitch and loudness are independent properties of a sound wave; either can be changed without affecting the other
  • A single tuning fork struck softly and then struck hard produces the same pitch each time; the trace keeps the same horizontal spacing but the second strike gives a taller wave
  • A flute playing a high note quietly and a tuba playing a low note loudly differ in both pitch and loudness simultaneously, but the two properties are independent in principle
Exam tip

State the wave property that determines pitch (or loudness)

What comes up: a one-mark question asking which wave property determines the pitch of a sound.

Write: frequency. Give only one property — the mark scheme credits frequency alone and rejects any response that names more than one quantity.

Watch out: do not write "frequency and wavelength" or "frequency and amplitude" — the mark scheme explicitly rejects an answer that names more than one quantity/property.