Concepts

Resonance, standing waves

Overview

A metal plate, with salt sprinkled on top of it, is mounted on a mechanical oscillator that is powered by a function generator. At specific frequencies, the salt accumulates at certain locations of the plate, representing nodal lines for the standing wave patterns of the system.

Details

Equipment

• [1] Function generator
• [1] BNC-banana cable
• [1] Mechanical vibrator
• [1] Square metal plate
• [1] Round metal plate
• [1] Container of salt
• [1] Brush
• [1] Paper box-top
• Metal shims
• [1] Overhead earmuffs
• Disposable earplugs

Classroom Assembly

1. Place the mechanical vibrator in the paper box.
2. Lock the vibrator.
3. Place a plate on top of the mechanical vibrator.
4. Unlock the vibrator.
5. Connect the function generator to the mechanical vibrator.
6. Level the plate by putting metal shims under the mechanical vibrator. If the plate is level, it should make fairly symmetric salt patterns at resonance. (Optional)

Important Notes

• Wear ear protection while driving the plate at high amplitude.

Script

1. Distribute earplugs to the students who want them. Advise the other students they may want to cover their ears.
   
2. Sprinkle salt uniformly on top of the plate. Spread it around with the brush as required.
3. Turn on the function generator.
4. Adjust the frequency of the signal generator to a resonance.
5. Remove excess salt with a brush, if required.
6. Repeat 1-4 for other resonances.
7. Repeat the experiment using the other plate.

Additional Resources