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6 marksPhysics of the Ear and Eye

CAPE Physics Unit 1 · 2007 · Paper 2 · Question 6(b)(iii)

A loudspeaker at a concert generates 1 x 10⁻² W m⁻² at a distance of 20 m from the speaker at a frequency of 1 kHz.

Given that the intensity (in W m⁻²) of the sound is inversely proportional to the distance, x, from the speaker (I ∝ 1/x²), find the distance at which the intensity level will be at the pain threshold of 120 dB. [Threshold intensity of hearing = 1 x 10⁻¹² W m⁻², Velocity of sound = 340 m s⁻¹]

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Other parts of this question

  1. 6(a)(i)Explain how such a wave may be formed from two progressive waves, CLEARLY indicating any conditions that MUST be fulfilled.[2 marks]
  2. 6(a)(ii)Compare the amplitudes of particle vibrations at A, B and C and the phases at B and C.[3 marks]
  3. 6(a)(iii)Give the THREE subjective sensations of sound and state what objective quantities are associated with them.[3 marks]
  4. 6(b)(i)Calculate the wavelength of the waves emitted by the loudspeaker.[3 marks]
  5. 6(b)(ii)What is the intensity level at 20 m?[3 marks]

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