Melde's Vibrating String, 3B22.10

Topic and Concept:

• Wave Motion, [:WaveMotion#StandingWaves: 3B22. Standing Waves]

Location:

• Cabinet: [:WavesSoundCabinet: Waves and Sound] (WS)

• Bay: (A4)

• Shelf: #1

attachment:MeldesString01-400.jpg

Description:

The Pasco driver controlled by a function generator vibrates an elastic cord. By varying the driving frequency and amplitude, one can produce standing waves. The nodes and the antinodes can be seen better by using strobe lights.

Setup:

1. Take the small ring stand with the elastic cord wrapped around it. Unwrap enough cord to stretch the cord across the lecture bench.
2. With the Pasco vibrator, take the looped end of the cord, string in through the forked tip, and attach to the base set screw that is typically used to hold rods. This will anchor the cord.
3. Place a lead brick in front of the vibrator to prevent the cord from pulling or tipping the the vibrator.
4. Place the strobe at each end of the cord in such a way that the strobe light are aimed at the cord and NOT at the students.

Cautions, Warnings, or Safety Concerns:

1. Strobe Lights can bother students with epilepsy. This warning should be stated in class before doing the demonstration.

Demonstration:

Set the function generator so that the cord vibrates at it's fundamental frequency. This frequency depends on the tension of the cord and will differ every time this demonstration is set up. Vary the driving frequency and amplitude to show the other modes of a standing wave fixed at both ends. Point out the nodes and the antinodes. Use the strobe lights to make the vibrating cord stand still or make it roll in slow motion.

References:

1. List any references

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