Experiment using Resonance Air column

Using the principle of resonance, the resonance air column equipment measures the sound velocity in room temperature air. Resonance happens at particular air column lengths when a tuning fork with a known frequency is struck and held above the air column. The velocity of sound in air can be computed by measuring these lengths.

Speed of sound: Resonance air column- Materials required

Resonance Air column apparatus: ( A long graduated glass tube with a movable water reservoir and a clamp stand to hold the resonance tube vertically).

Tuning forks of known frequencies (e.g., 256,288,340,412 and 512}

Rubber hammer or striker

Rubber Pad

Thermometer (For to measure the lab temperature) and

Water

Speed of sound: Resonance air column- Formula

Resonance Air Column Apparatus -Image

Resonance air column:Speed of sound-Experimental Setup

Using a clamp stand, position the resonance tube vertically.

Pour some water into the tube. The water reservoir can be moved up or down to change the water level.

Make sure there is no damage or dirt on the tuning fork.

Use the thermometer to determine the room temperature.

Speed of Sound: Resonance Air Column -Procedure

First Harmonic (First Resonance):

Holding the tuning fork horizontally just above the resonance tube’s open end, lightly strike it with the rubber hammer.

Move the reservoir downward to gradually reduce the water level in the tube. Keep an ear out for a sudden rise in resonance, or sound intensity.

First Resonating length

The air section over the water level is constrained(forced) with a tuning fork of suitable frequency. We get the main (first) resonance condition at a stature in which the natural frequency is equivalent to the forced frequency.

For a length of l1, we get the main(first) resonance condition (booming sound).

Second Resonance (Third Harmonic):

Continue lowering the water further until you hear another increase in sound intensity(booming sound) which is the second resonance.

Second Resonating Length

Further assuming we bring down the water level in the reverberation tube by changing the repository(reservoir) to get the subsequent (second) resonance condition.

The second resounding(resonating) length is taken as l2.

First and Second resonating length -Image

Repeat for Different Frequencies

Repeat the experiment for different frequencies and find the resonating lengths in each case to ensure accuracy.

Speed of sound- Resonance Air column – Tabular column

S.No.	Frequency of  the tuning fork                         Hz	First resonating  length l1                    cm	Second resonating length l2             cm	Speed of sound                  m/s
1.	256	32.0	96.0	327.68
2.	288	30.0	90.0	345.60
3.	320	28.0	84.0	358.40
4.	341	27.0	81.0	368.28
5.	384	25.0	75.0	384.00

Speed of sound: Resonance air column-Precautions:

Ensure the tuning fork is struck gently to avoid damage.

Measure the lengths l1 and l2 accurately.

Perform the experiment in a quiet environment to clearly hear the resonance.

Ensure the resonance tube is vertical to avoid errors in measurement.

Speed of sound: Resonance air column-Result

The velocity of sound in air at the lab temperature 26 degree Celsius(at the lab temperature) is found to be 356.79 m/s

Theoretical speed of sound at 26 degree Celsius is 346.6 m/s

The experimental value is slightly higher possibly due to errors like end correction,ambient conditions and tuning fork calibration

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