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Homework Help: Maximums on a Diffraction Grating

  1. Jul 31, 2013 #1
    1. The problem statement, all variables and given/known data

    Consider an array of parallel wires with uniform spacing of 1.40 cm between centers. In air at 20.0°C, ultrasound with a frequency of 35.6 kHz from a distant source is incident perpendicular to the array. (Take the speed of sound to be 343 m/s.)

    (a) Find the number of directions on the other side of the array in which there is a maximum of intensity. (State the number of angles for which there is a maximum of intensity. An angle above the horizontal and an angle below the horizontal count as two separate angles. If there is a maximum at the horizontal, it also counts as an angle.)

    (b) Find the angle for each of these directions relative to the direction of the incident beam. (State the angles corresponding to maxima of intensity for each value of m. If there does not exist a maximum of intensity for a given value of m, enter 'NONE' in the answer blank.)

    2. Relevant equations

    d sin θ = mλ

    3. The attempt at a solution

    I really have no idea. I know that this is a diffraction problem, but that's about it. I feel like giving the speed of sound is the hint in the question, but I don't see the relevance...
  2. jcsd
  3. Jul 31, 2013 #2


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    Homework Helper

    How do you get the wavelength λ from the speed of the wave and from its frequency?

  4. Jul 31, 2013 #3
    You are on the right track. It is useful to know the wavelength of the waves..... Can you get that from what you have been given?
  5. Jul 31, 2013 #4
    I got it, that helped me along. What was throwing me off was that for some reason I thought I needed to know how many lines there were. Thanks!
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