To Find Velocity Of Sound By Resonance Air Column Method

APPARATUS REQUIRED:-

• Turning fork
• Rubber pad
• Resonance apparatus.

THEORY

A vibrating tuning fork held slightly above the free end of the resonance tube forces the air columns in it to vibrate and sets up stationary waves in it. While adjusting the length of the air columns a position will be obtained when the intensity of the sound will be maximum. This will occur when the frequency of the vibrating air columns will be the Same as that of the tuning fork. There will be the same as that of the tuning fork. There will be an antinode at the open end and node at the closed end. In this a position for the 1st resonance.

V=μf (L₁N). --- (i) 

where,

•  v velocity of sound.
• f frequency of the turning fork.
• L₁ length of the first resonance air columns.
• N end Condition (0.3d, d is the internal diam- eter of tube)

for the second resonance 

    V = (4f)/3 * (L₂ + N)

3V = 4f ( L₂ + N ) --- (ii)

where,  L₂ = length of the and resonance

from i & ii. By Subtraction,

   V = 2f(L₂ - L₁)

This gives the velocity of sound in the lab to convert it into velocity in dry air at NTP,

we have,

Ve = v  sqrt((p - 0.375f) / p) *  (1 - 1/2 * at)

where,

• P= alm pressure in cm in lab.
• f = aq tension at the lab temperature.  
• Alpha =  coefficient of linear expansion.
• t = lab temperature.

PROCEDURE

• The tuning tuning fork was struck against a rubber pad and was held slightly above free end of the tube. The water level was an approximate resonance was adjusted fill was obtained with the smallest length of the air coloumn.
• The length of the air coloumn was adjusted properly. by raising lowering the water level till maximum resonance was obtained. This was adjusted resonance once by gradually increasing the length of air column and next decreasing it.
• These operations were repeated at least three times.The mean air column. was taken as the 1st resonance
• The length of the air column was gradually increased fill the second resonance was heard. The mean was taken as in (iii) Then the velocity  was calculated by using the above formula.
• The Barometer reading was taken. The lab. temp was noted. The aq. tension at lab temperature was found out from the physical tables. Then "V" was calculated

OBSERVATION

• Barometer reading = 74 cm of Hg
• laboratory temperature = 29°c 
• Coefficient of linear expansion (Alpha) = 1/273

OBSERVATION TABLE

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