A Method of Determining the Frequency of a Tuning Fork

Abstract

IN an experiment performed in this laboratory on the determination of surface tensions of liquids by the method of ripples, a tuning fork, provided with a dipper and slits on the two prongs, was used to produce the ripples as well as to illuminate the surface of the liquid by intermittent light, obtained by passing a narrow beam of sunlight through these slits and reflecting it on the surface by a plain mirror. It thus became necessary to determine accurately the frequency of the tuning fork with all its encumbrances. Evidently the ordinary graphic method could not be used without introducing more complications and thus altering the frequency, and means were not available of utilising the stroboscopic method. The frequency was, therefore, determined in terms of the length, or the time of vibration, of a simple pendulum hung in front of the slits of the prongs. The light, after passing the two prong slits, passed immediately above the bob of the pendulum, illuminating a small cross which connected the bob to the suspending thread. The light ultimately fell on a drum round which could be wrapped an ordinary photographic film.