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An ultrasound machine in a hospital uses a sound source at 19.00000MHz. [3 marks] Assuming that...

An ultrasound machine in a hospital uses a sound source at 19.00000MHz.

  1. [3 marks] Assuming that the speed of the ultrasound in the body is same as water (1440 m/s), determine the wavelength in the body.
  2. [6 marks] If blood cells are moving towards the sound source at a speed of 0.8 m/s, at what frequency do the crests of the sound wave pass through the blood cell?
  3. [5 marks] What is the frequency of the sound waves reflected back towards the source by the blood cells?
  4. [6 marks]
    1. If the sound level intensity is 17.0 dB at a point d1 = 6.8 cm from the source, what is the sound intensity at that point in W/m2. (We can assume that 0 dB is referenced to 10-12 W/m2).
    2. Assume that sound is emitted from a point source, so that the intensity decreases quadratically with distance. What is the intensity level in dB at a point d2 = 2.0cm from the source?
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