Question
A ripple tank has two locations (L1 and L2) that vibrate in tandem as shown below. Both L1 and L2 vibrate in a plane perpendicular to the page, creating a two-dimensional interference pattern.
Describe an experimental procedure to determine the speed of the waves created within the water, including all additional equipment that you would need. You may use the diagram below to help your description, or you may create one of your own. Include enough detail so that another student could carry out your experiment.
Final Answer
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Solution video
OpenStax College Physics for AP® Courses, Chapter 17, Problem 12 (Test Prep for AP® Courses)
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Video Transcript
This is College Physics Answers with Shaun Dychko. This situation reminds me of this picture from chapter 16 where we have two sound sources with the same frequency causing constructive and destructive interference depending on which part of the picture you look at. So when you have a compression wave or a point of compression in the sound from one source matching up with a compression from the other source, you have constructive interference and that occurs at points A, E, D and C. You also have constructive interference at this point B here but these are negative antinodes or rarefaction from one source meeting rarefaction from another source. So if you look at the interference pattern from the vibrators that are in this ripple tank, you should find a point that's similar to point E here and D and these peaks should occur at the same time and the distance between them is the wavelength and so this would be in our picture, it would be like this and this these would be two points of say compression or something analogous to compression or maximum height of the water wave and so using a ruler, measure the distance here— in this, it will be the wavelength— so the distance between two adjacent peaks. And then the next thing you need to know is the period of the wave and you can use a stopwatch to measure that and so we could observe a single peak here let's say we observe just this peak and it will become a significant trough and then a high peak and then a trough and then over and over again and measure the time it takes for ten peaks to occur— I just made up the number 10... some number of peaks— and then the period is going to be the total time that you have measured using a stopwatch divided by 10 and the wave speed then will be this wavelength you measure with the ruler in this first step and then divide that by the period.