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3.3.2Stoichiometry

Sound and Oscilloscopes — Cambridge IGCSE Chemistry 0620 Revision Notes & Topical Questions

5 min read 4 parts Lesson 24 of 28 Unit quiz

📚 Cambridge IGCSE Chemistry 0620 Hub / Topical Revision
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Curriculum Equation Key Wave Speed & Doppler Effect FormulasFast Exam Solution
v = f × λ | f_obs = f × (v ± v_o) / (v ∓ v_s) | T = 1 / f
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Section 1 of 4Reading the Display

3.3.2 Sound and Oscilloscopes

An oscilloscope draws a sound wave as a trace, so the screen axes have different meanings from a real wave diagram.

Horizontal axis
  • The horizontal axis is the time base, so a full cycle of the trace can be used to measure the time period.
Vertical axis
  • The height of the trace from the centre line is related to the amplitude of the sound wave.
Number of waves
  • The number of complete waves across the screen is related to the frequency of the sound.
Longitudinal display
  • A longitudinal sound wave is displayed as a transverse-looking trace, even though the air particles move parallel to the wave.

Section 2 of 4Pitch and Loudness

Pitch and Loudness
Pitch
  • Pitch depends on frequency, so a sound with a higher frequency has a higher pitch.
Loudness
  • Loudness depends on amplitude, so a sound with a larger amplitude is louder.
Changing frequency
  • Changing the frequency alone changes the pitch of the sound but not its loudness.
Hearing range
  • Humans can hear frequencies from 20 Hz to 20 000 Hz, with infrasound below and ultrasound above this range.

Section 3 of 4Comparing Two Traces

1
Find the time period of each trace by measuring the time for one full wave across the grid.
2
A trace with a shorter time period has a higher frequency and therefore a higher pitch.
3
A trace with a greater height from the centre line has a larger amplitude and is therefore louder.
4
Compare the two traces for both spacing and height before drawing any conclusion about the sounds.

Section 4 of 4Exam Checklist & Tips

3.3.2 – Key Points for the Exam

  • Oscilloscope A device that displays a rapidly changing signal, such as a sound wave, as a trace on a screen.
  • Time base The horizontal scale of an oscilloscope, used to measure the time period of a wave.
  • Amplitude The maximum displacement of a wave from its rest position, which determines the loudness of a sound.
  • Pitch How high or low a sound is perceived to be, which depends on its frequency.
  • Infrasound Sound with a frequency below 20 Hz, which humans cannot hear.
  • Ultrasound Sound with a frequency above 20 000 Hz, which humans cannot hear.

Common Mistakes

  • Assuming that a wave with a larger amplitude has a higher pitch; amplitude affects loudness, not pitch.
  • Confusing loudness with pitch when comparing two traces.
  • Describing a sound of 25 000 Hz as audible; frequencies above 20 000 Hz are ultrasound.
  • Treating the time base as the vertical scale; the time base is the horizontal axis.

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