Purpose: To demonstrate standing waves in an air column.

A sets of telescoping, nested tubes with a cap to close the end; tuning fork set, mallet.

Clamp the large tube to the desktop. Calculate the possible lengths of a closed air column for standing waves of 1000 Hz in room-temperature air. Note that the first few harmonics need a tube shorter than is possible with the given apparatus. For the lowest harmonic for which the resonant length exceeds that of the large tube, move the inner tubes back and forth in the vicinity of the calculated length while holding the vibrating tuning fork near the open end. There should be a noticeable rise in loudness near resonance. Do the same for higher harmonics. Discuss the mechanism of reflection of waves from the closed end of the tube.

Ask students if standing waves would occur if the end were open. Most will probably think not. Demonstrate that standing waves do occur with comparable intensity. Discuss standing waves in an open pipe, calculate the resonant lengths, and demonstrate agreement.

References:

Manual: None