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Learning Introductory Physics with Activities

Paul J. Emigh, Rebecka Tumblin, Kathryn Hadley, Danielle Skinner

Section 18.13 Interference in 2D

Subsubsection Activities

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Activity 18.13.1. Crests and Troughs.

The figure below shows two overlapping periodic circular waves, their sources separated by some known distance. The solid lines represent successive wave crests and the dotted lines represent wave troughs.
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Figure 18.13.1. Two overlapping circular waves.
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(a)

Locate several places on the diagram where two wave crests meet. Do these points correspond to constructive or destructive interference?
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(b)

Locate several places on the diagram where a wave crest meets a wave trough. Do these points correspond to constructive or destructive interference?
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Activity 18.13.2. Path-length Difference.

The figure from above has been reproduced below, with several points labeled A-F.
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Figure 18.13.2. Two overlapping circular waves with several points marked.
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(a)

For each labeled point, determine the value of the path length difference \(\Delta D\) as a multiple of the wavelength \(\lambda\text{.}\)
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(b)

For each labeled point, find at least two other points that have the exact save value of \(\Delta D\) as a multiple of the wavelength \(\lambda\text{.}\)
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The figure from above has been reproduced below, with all points with maximum constructive interference connected in orange and all points with complete destructive interference connected in black.
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Figure 18.13.3. Two overlapping circular waves with interference lines marked.
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