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Measurement of the Velocity of Sound by a Resonance Tube

المؤلف:  GEORGE A. HOADLEY

المصدر:  ESSENTIALS OF PHYSICS

الجزء والصفحة:  p-205

2025-11-16

629

It is possible to compute the velocity of sound in air by measuring the length of the air column in the resonance tube, and combining this properly with the number of vibrations per second. A convenient form of tube and support for this measurement is shown in, Fig. 1. The glass tube A is connected by a flexible rubber tube to a similar glass tube fastened to the movable wooden arm B. This arm moves with so much friction that it will stay in any position. The support for the tuning fork is so arranged that forks of various lengths may be held in position. By pouring water into the tube and moving B toward or from the vertical position, the length of the air column in A can be so fixed that it will give a maximum reënforcement to the sound of the fork. When this is carefully determined, the length of the air column can be read on the millimeter scale

back of A, which is graduated from the position of the fork as zero. To find the velocity of sound from this measurement it must be remembered that since the pulse of air first given out by the fork must go to the bottom of the tube and back, that is, twice the length of the tube, while the fork is making half of a complete vibration, it will go four times that length while the fork is making a complete vibration. This means that the wave length of the fork is 4 times the length of the air column. Calling the length of the air column I and substituting the value 4 l in Formula

we have v = 4 lN. Experiments with tubes of different diameters, however, show that a correction must be made for the diameter; that is, in order to get correct results a certain fraction of the diameter must be added to the length of the air column to give one fourth of the actual wave length. Lord Rayleigh finds this fraction to be nearly four tenths the diameter. Including this correction in the formula, we have