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3.3.4Stoichiometry

Pitch and Loudness — Cambridge IGCSE Chemistry 0620 Revision Notes & Topical Questions

5 min read 5 parts Lesson 26 of 28 Unit quiz

📚 Cambridge IGCSE Chemistry 0620 Hub / Topical Revision
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Part 1 of 5Pitch and Frequency

3.3.4 Pitch and Loudness

Pitch is how high or low a sound seems to a listener, and it is set by the frequency of the vibrating source.

High pitch
  • A sound produced by a high frequency of vibration has a high pitch, such as a whistle or a bird song.
Low pitch
  • A sound produced by a low frequency of vibration has a low pitch, such as a large bass drum.
Frequency
  • The number of complete waves passing a point each second, measured in hertz (Hz).
Period
  • The time for one complete wave to pass a point, found from T = 1 ÷ f and measured in seconds.

Part 2 of 5Loudness and Amplitude

Loudness depends on the amplitude of the wave, which is the maximum displacement from the rest position.

Loudness and Amplitude
Loudness
  • The loudness of a sound is related to the amplitude of the vibrations that produce it.
Large amplitude
  • A large amplitude gives a loud sound because the vibrating source moves through a greater distance.
Small amplitude
  • A small amplitude gives a quiet sound, and changing it does not alter the pitch of the note.
Oscilloscope
  • On an oscilloscope amplitude is shown as the height of the trace and the period as horizontal distance.
Change to the waveEffect on pitchEffect on loudness
Higher frequencyHigherNo change
Lower frequencyLowerNo change
Larger amplitudeNo changeLouder
Smaller amplitudeNo changeQuieter

Part 3 of 5Range of Hearing

Human hearing covers a fixed band of frequencies, with sounds outside it having special names.

1
Humans can normally hear sound with frequencies between about 20 Hz and 20 000 Hz.
2
Sound below 20 Hz is called infrasound, which people cannot hear, although some animals such as elephants can detect it.
3
Sound above 20 000 Hz is called ultrasound, which is used in medical scans and in industrial cleaning equipment.
4
The upper limit of hearing usually falls with age, so older people often cannot hear the highest pitches.

Part 4 of 5Worked Example

Question

  • An oscilloscope trace shows 5 complete waves in a time of 0.010 s.
  • Calculate the frequency of the sound.

  1. Frequency is the number of complete waves produced each second, so f = number of waves ÷ time taken.
  2. Substitute the valuesf = 5 ÷ 0.010 s.
  3. f = 500 Hz.

Answer The frequency is 500 Hz, which lies inside the human hearing range, so the sound would be audible with a fairly high pitch.

Part 5 of 5Exam Checklist & Tips

3.3.4 – Key Points for the Exam

  • Pitch How high or low a sound is perceived to be, set by its frequency.
  • Loudness How loud a sound is perceived to be, set by the amplitude of the wave.
  • Frequency The number of complete waves passing a point per second, in hertz.
  • Amplitude The maximum displacement of a wave from its rest position.
  • Infrasound Sound with a frequency below the range of human hearing, under 20 Hz.
  • Ultrasound Sound with a frequency above the range of human hearing, over 20 000 Hz.

Common Mistakes

  • Saying a louder sound has a higher pitch; loudness depends on amplitude while pitch depends on frequency.
  • Confusing amplitude with frequency or wavelength when describing a wave on an oscilloscope.
  • Using a period in milliseconds without converting to seconds before calculating frequency.
  • Describing ultrasound as sound that people can hear because it is high pitched.

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