TY - JOUR
AB - Prof. Fleming exhibited an apparatus for the production of vibrations on strings loaded or unloaded. This method is an improvement on that of Melde, in which transverse vibrations are created on a string attached to the prong of a tuning fork.Melde's method has the disadvantage that it is not possible to put great tension on the string without stopping the fork, or to use very heavy or loaded strings without using forks of great size. Moreover, the frequency cannot be varied except by changing the fork.In the Author's method the vibrations are produced on a string by attaching one end to the shaft of a small continuous-current motor of about 1/8 H.P. The motor has on one end of its shaft a mechanism for counting revolutions, and on the other end a disc which has a crank pin inserted in its outer face, and to this pin is attached a light crankshaft connected at its outer extremity with a rocking lever. The string is fastened to a hook on the crankshaft near to the crank pin.The other end of the string is attached to a fixed point which can be moved by means of a screw, in some cases a spring balance being interposed to measure the tension.When the motor is started the string has a circular motion given to its end which is equivalent to two simple harmonic motions at right angles to each other.If the tension is rightly adjusted the string then vibrates in sections, and the number of sections can be adjusted by altering the tension. The distance from node to node can then easily be measured and the frequency determined from the speed of the motor. In this way the velocity of the wave is measured, and can be compared with the velocity determined by taking the square root of the quotient of the tension by the linear density of the string.A number of tables were exhibited showing the velocity of the wave motion on strings of various kinds confirming the known laws of string vibrations.This method is particularly useful in studying the properties of loaded strings. Strings made of flexible cotton cord can be loaded with glass or wooden beads and set in vibration. In this manner it can be shown experimentally that when the wave length on the string extends over a distance of more than 8 or 10 loads, the string vibrates as if the loading matter were uniformly distributed, but the string cannot propagate vibrations when the half wave length approaches equality to the distance between two loads.It is also possible to show by this apparatus very prettily the reflection of a wave at a load placed at any point on the string, and also that this reflection is reduced by tapering off the loading.We can thus imitate with this loaded vibrating string all the phenomena of inductive loading in telephone cables on the Pupin system.The theory of the vibrations of a loaded string has been studied by many mathematicians - for example, by Lagrange, Lord Rayleigh, Prof. P. G. Tait, and a very interesting Paper was published on the subject by Mr. Charles Godfrey in the "Philosophical Magazine" for April, 1898.This method of causing a string to vibrate by a motor affords a simple method of demonstrating all the laws of vibrating strings to a class
TI - An Experimental Method for the Production of Vibrations on Strings illustrating the Properties of Loaded or Unloaded Telephone Cables
JF - Proceedings of the Physical Society of London
DO - 10.1088/1478-7814/26/1/306
DA - 1913-12-01
UR - https://www.deepdyve.com/lp/iop-publishing/an-experimental-method-for-the-production-of-vibrations-on-strings-Goe401meOh
SP - 61
VL - 26
IS - 1
DP - DeepDyve
ER -