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Homework Help: Applying principle of superposition to draw resultant shapes. Please help!

  1. Apr 9, 2012 #1
    1. The problem statement, all variables and given/known data

    Apply the principle of superposition to draw the resultant shape when each of the sets of pulses shown interferes. (Draw the diagrams so that the horizontal midpoints of the pulses coincide.)

    2. Relevant equations

    Please check this website: http://myclass.peelschools.org/sec/11/22607/Lessons/Unit 4 Sound/Review Chapter 6.pdf and look at #20, page 2. I have to do every diagram but I want to learn and so letter a.

    3. The attempt at a solution

    Do I draw amplitude arrows going down.. eek, I'm so confused, please help!
  2. jcsd
  3. Apr 9, 2012 #2
    I think there are a variety of ways to do problems like this. Though it's been a while since I did this kind of thing so perhaps someone has a better way.

    To get a better understanding, note that the first (big) pulse is:

    Length/Pulse Width: 6 units
    Height/Amplitude: 3 units

    The second pulse has:

    Length/Pulse Width: 3 units
    Height/Amplitude: 1.5 units

    it's also in the negative y-axis.

    Both these pulses are traveling towards each other in the x-axis.

    So what is essentially going to happen when they combine; what would you expect the resultant pulse to look like? Bigger than the first pulse? Smaller?

    Remember, if both these pulses were on the positive y-axis heading towards each other, they would add to each other, but since one is in negative and the other is in the postive, the resultant would be a subtraction. The question asks what it would look like at the mid-point of their intersection/superposition.

    Read through the concept of constructive and destructive interference:


    It might also help to do (b) and (c) first before doing (a), those are somewhat simpler to understand.
    Last edited: Apr 9, 2012
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