Equipment:

• Function Generator
• Oscilloscope
• Resonating Tube Setup, including speaker, microphone (in tube) and amplifier

Demo:

This device is used to demonstrate sound resonance, determine the speed of sound, and show the acoustics of musical wind instruments.

The plexiglass column, 1.5 m long and 7 cm in diameter, is filled with water. Water is slowly released by a valve (D). A speaker (A) at the top is set for a frequency between 500-700 Hz. A powerful functional generator controls this frequency. The ruler on the back is magnified by water and helps to determine the points where the sound reaches maximum intensity. A microphone (B) attached below the speaker and connected to the oscilloscope through an amplifier (C) makes the determination of resonant points more accurate. After resonances are noted, and the wavelength is measured (see picture to the left), it is easy to calculate the speed of sound.

To show the audience how the organ tubes and other musical wind instruments work, the plexiglass column is used without water, and a microphone slides slowly down the column showing nodes and anti-nodes on the oscilloscope screen.

Note: Make sure that the microphone stays dry when performing experiments with water.

Explanation: