Physics 122 Week 7
Standing Waves
Standing Slinky Wave
Have a student hold one end of the slinky, and then oscillate the other end to create various standing waves.
Standing Wave from Speaker
Attach one end of the string to a fixed pole secured to the desk, connect the other end to a pole and clamp the speaker to it close to that end. Using a frequency generator various standing waves can be created, but make sure the string is level!
Standing Wave Model
The red beads illustrate the superposition of the black wave drawn on the background, and the wave created by the green beads from pushing the cut out through the housing.
Resonance Cavities and Beats
Rijke Tubes
This is a great demo to heat things up in your lectures.... Hold the cardboard tube over a lit Bunsen burner, and lower it until the air inside begins to resonate. Two can be used in tandem to create beats. ** If using two burners, make sure to always light both when the gas is turned on.**
Resonance in Open-Closed Tube
After striking a tuning fork (512 Hz), hold it a few cm above an open-ended tube in water. Raise/lower the tube until a standing wave is created resonating with the tuning fork.
Resonance in Open-Open Tube
Just like above, but sliding the inner tube back and forth varies tube length. You can even measure the tube length and show students how to mathematically predict the next resonant length!
Large Resonance Tube
After hooking up a speaker to a function generator and placing it at the tube's opening, you can lengthen the air column until you hear resonance! Use the ruler printed on the white column to get quantitative data to help predict the next resonant location.
Driven Resonator
Attaching a motor to this spring supported table allows it to resonate with the attached hacksaw blades. Make sure to press it firmly to the counter or it will start to wiggle away!
Dual Function Generator with Speakers
- Nodes and Antinodes: When both speakers are plugged into the same output, their sound waves will interfere within the classroom. Have your students walk around to locate the nods and anti-nodes, or pick up the speakers and rotate them.
- Beats: Plug each speaker into a separate output, and adjust frequencies to create beats.
-Destructive Interference: Plug both speakers into the same output, but switch the leads for one of the speakers. Then, face the speakers towards each other.
Beat Bars
Adjust the clamps on each tuning fork in order to change their frequency. Once they are close to the same height, strike the forks on the opposite side of the clamp to hear some beats!
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