To investigate the resonant frequency of the fundamental mode of vibration of air in a container

Procedure

This experiment can be investigated by using a resonance tube, and a set of tuning forks. The volume of air in the tube can be changed by moving the inner tube up and down. The width of the inner tube will not change throughout the whole experiment- making it a fair test. Also different tuning forks can be used to give a varied range of frequencies so that I see how the fundamental mode is affected by the change in frequency. The fundamental mode is formed at ?/4 (one quarter of the wavelength), and the next mode is formed at 3?/4 (3 quarters of the wavelength), but only the fundamental mode is going to be investigated.

Pipes in a pipe organ work on this basis. Air enters at the foot of the pipe, moves against a narrow slit or flue, and begins to vibrate as it passes across a sharp lip set in the pipe above the flue. This initial vibration causes all the air in the pipe to vibrate, producing a musical tone. The pitch of the note depends on the length of the pipe (the volume of air). Some flue pipes are closed at the top; "stopped" pipes produce pitches one octave lower than the pipes of the same length. This could also be investigated in the experiment, but not by using the resonance tube.

Method

The volume of air will be measured by calculating the cross-sectional area of the inner tube and then measure the length of the tube, which is not submerged in the water. Multiplying the two values together will give the volume of air in the tube. The cross-sectional area of the inner tube will remain constant throughout the whole experiment. The fundamental mode of vibration will be found when the note of the tuning fork is amplified- creating the stationary wave.

The tuning fork will be placed just over the top of the inner tube and the tube will then be moved up and down until the fundamental mode is found. This will be repeated with different tuning forks for different frequencies. Both of the tubes will have to be made from glass or some other form transparent material in order to see where the water level is, so that the volume of air can be measured accurately.

Care will have to be taken so that the inner tube is not just suddenly dropped, be cause it will be made out of glass and likely to break. Also there must be care taken when handling water- not to spill it o the floor because it could make the floor slippery and be careful not to take the water near any electrical equipment.

Anthony Quinn