Interference wave have solution need explanation

  1. 1. The problem statement, all variables and given/known data
    In Fig. 17-35, sound with a 46.4 cm wavelength travels rightward from a source and through a tube that consists of a straight portion and a half-circle. Part of the sound wave travels through the half-circle and then rejoins the rest of the wave, which goes directly through the straight portion. This rejoining results in interference. What is the smallest radius r (cm) that results in an intensity minimum at the detector? (Take the speed of sound to be 343 m/s.)

    2. Relevant equations
    3. The attempt at a solution

    i have the solution...what i don't understand is WHY the path length difference equals 23.2??? don't see how or why it's half the wavelength???
  2. jcsd
  3. Hootenanny

    Hootenanny 9,676
    Staff Emeritus
    Science Advisor
    Gold Member

    HINT: A minimum means that destructive interference has occured ...
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