Resonance air column apparatus
resonance air column apparatus consists of a glass tube G about one metre in
length (Fig.) whose lower end is connected to a reservoir R by a rubber tube.
glass tube is mounted on a vertical stand with a scale attached to it. The
glass tube is partly filled with water. The level of water in the tube can be
adjusted by raising or lowering the reservoir.
vibrating tuning fork of frequency n is held near the open end of the tube. The
length of the air column is adjusted by changing the water level. The air
column of the tube acts like a closed organ pipe. When this air column
resonates with the frequency of the fork the intensity of sound is maximum.
longitudinal stationary wave is formed with node at the water surface and an
antinode near the open end. If l1 is the length of the resonating
e is the end correction.
length of air column is increased until it resonates again with the tuning
fork. If l2 is the length
of the air column.
λ/4 = l2 +e ????..(2)
equations (1) and (2)
= (l2 - l1)
velocity of sound in air at room temperature
= nλ = 2n (l2 ? l1) ...(4)
antinode is not exactly formed at the open end, but at a small distance above
the open end. This is called the end correction.
l1 + e = λ/4
+ e = 3λ4
is found that e = 0.61r, where r is the radius of the glass tube.