Experiment 14
Resonance and the Velocity of Sound

Objectives
To use resonance conditions to measure wavelengths and speed of sound waves. 

Introduction
Sound is a wave phenomenon and so the usual relation 

v = λf

holds for frequency, wavelength and velocity.  In a tube closed at one end, standing waves occur when the tube length is ¼ λ, 3 λ/4, 5 λ/4, etc.  These lengths then define the "resonance conditions" where the sound is strongly reinforced because of the constructive superposition of transmitted and reflected waves down the tube.  They occur only when a node occurs at the closed end and an antinode at the open end.

In this experiment we will alter the length of a tube by changing the water level in the tube.  The water closes one end of the tube.

Procedure

 1)            With the tuning fork clamped above the tube so the motion of the prongs is vertical, find as many positions as possible where resonance occurs.  Each position should be located as precisely as possible by passing it several times in both directions.

 2)            Record the temperature in the room.

 3)            Repeat Procedures 1 and 2 outside.  Take the apparatus outside and allow it to warm.  After a few minutes, raise the water level as high as possible to push out any inside air remaining in the tube.

 4)            Find the velocity of sound for each repetition of Procedure 1 and check your values against known values calculated from the formula