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8 marksProperties of Waves

CAPE Physics Unit 1 · 2010 · Paper 2 · Question 5(b)(iii)

Figure 7 shows a loudspeaker connected to an audio-frequency signal generator/amplifier set up in front of a large flat wall. A small microphone detects regions of low and high intensity between the speaker and the wall.

When the signal generator is set at 165 Hz how far from the wall is the last maximum intensity position? [Velocity of sound = 330 m s⁻¹]

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Other parts of this question

  1. 5(a)(i)Explain what is meant by 'threshold of hearing' and 'threshold of pain'.[1 mark]
  2. 5(a)(ii)What property of the human ear makes the decibel (dB) scale particularly useful?[1 mark]
  3. 5(a)(iii)Write down an expression that relates the sound intensity I, to the intensity level β, in dB.[1 mark]
  4. 5(a)(iv)What is the intensity level of a sound with intensity 3.82 mW m⁻²?[1 mark]
  5. 5(a)(v)Figure 6 is drawn for a typical human ear. Suggest how the figure might change as a person ages.[7 marks]
  6. 5(b)(i)Explain why there are positions between the speaker and the wall where intensity is a minimum and why these minima do NOT actually have zero intensity.[1 mark]
  7. 5(b)(ii)The points labelled X on Figure 7 are the only three points of minimum intensity detected at a certain frequency setting. What is the frequency?[1 mark]

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