PhysicsLAB Lab
Directions: Constructive and Destructive Interference

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Shown below in Step 1 are two independent waves (one pink and one blue) traveling through the same medium in the same direction - towards the right. The waves have different amplitudes and wavelengths. Since they are simultaneously traveling through the same medium, their wave actions will interact, or interfere, with each other.
 
Step 1
 
When these waves actually travel through the medium, we do not see the original pink and blue waves, we see the interference, or resultant, wave shown below in green in Step 2. In your lab, all of your waves will be presented in the form of Step 2 with the interference, or resultant, wave already calculated and marked.
 
Step 2
 
To determine in which regions the waves are reinforcing each other (constructive interference) and in which regions they are canceling each other (destructive interference), we must first shade in the resultant green wave to the x-axis as shown below in Step 3.
 
Step 3
 
In order to determine where the regions of constructive and destructive interference begin and end, we must mark the entrance and exit points for each of the original waves (pink and blue) with the shaded regions. These points have been marked with dots in the diagram shown below is Step 4.
 
Step 4
 
Next we connect the dots with vertical lines to delineate each region as shown in Step 5.
 
Step 5
 
Finally, we mark the region as either a "C" for constructive, or a "D" for destructive as shown in Step 6. A region is labeled as constructive if the original wave amplitudes are "inside the shading" and reinforce each other by either both acting to move the medium up or both act to move the medium down. A region is labeled as destructive if the original wave amplitudes are "outside the shading" illustrating that they pull the medium in opposite directions.
 
Step 6
 
Notice that the regions of constructive and destructive interference alternate with respect to each other.
 



 
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