LecDem Blog

Details

Published: 08 May 2020

• physics
• mechanics
• simulation
• oscillations & waves

.Welcome back! This week, we’re looking at one of our particularly popular and versatile demonstrations, the Ripple Tank.

 The Physics Demonstration Facility has two versions of this demo, so we can reach as many audiences as possible. We have a table top version for outreach events and local classrooms, and a portable version to reach out-of-building locations. These ripple tank demonstrations can both be used to highlight a variety of wave phenomena.

A properly set up ripple tank with its various accessories, can illustrate many different aspects of the physics of waves – single and double point source circular waves, plane waves, interference, diffraction through openings and around obstacles. With a movable mount and careful planning, it can even show the Doppler effect!

Some of this is hard to do at home, but fortunately, there are options. Simulators exist that can carry out at least some of the experiments you might usually use the ripple tank for. You can take screenshots of them to illustrate lectures, or send the link to students to experiment with at home.

There are several different ripple tank simulators, such as this versatile one from Paul Falstad: http://www.falstad.com/ripple/ 

• When first opened, the simulator defaults to emulating a tank of water with a single oscillating source in it. It is tinted a cerulean color for easy viewing, but can be switched to several different color schemes via a drop-down menu. If you prefer the traditional view, #4 on that menu is a greyscale view that closely approximates the familiar shadow projection of the tabletop ripple tank.

• A checkbox below this allows the simulation to be frozen and restarted; another lets you shift to an angled three-dimensional view that can be more difficult to see on small screens, but can be helpful in clarifying complex wave behaviour.

• Sliders adjacent to this let you vary the frequency of the oscillation, and turn on damping.

• Other sliders let you adjust aspects of the simulation process, changing the speed, brightness, and resolution of the simulation box; these are best left alone unless you are struggling with making it work on a slower computer or are having difficulty clarifying complex wave behaviour at an interface.

• In addition to the preprogrammed oscillators, you can excite the simulated ripple tank manually by clicking on it, just like dipping your finger into the water of a real ripple tank.

• A variety of oscillation sources and tank configurations can be selected from the Example dropdown menu. Some likely to be useful for our purposes include:

1. Single Source and Double Source for circular waves from point sources

2. Plane Wave (which does show edge effects at the sides of the “tank”)

3. Single Slit and Double Slit which show diffraction via a plane wave striking a barrier with one or two holes and producing the expected circular waves and interference pattern

4. Obstacle (with a single source circular wave and a small rectangular barrier)

5. Doppler Effect 1 (with a moving source of circular waves).

• For more complex uses, you can also modify the simulation. By right-clicking in the simulation box, you can place additional sources, barriers, and refracting elements. You can also right-click on existing elements and delete them, allowing you to clear the screen and produce an empty “tank” to create your own experiment in.

• You can also place “probes” that will display the wave pattern at that point in a movable oscilloscope-style box. This can be valuable as a challenge for students, to predict the pattern that a probe would read at a given point, or to construct a simulation to produce a particular result.