Question
Discuss the theory of Quincke's tube to demonstrate the interference of sound wave.
Solution
i) The Quincke's tube consists of a U-tube D1 that can slide into another U-tube D2 as shown in the figure.
ii) The tube D2 has two openings.
iii) At one opening a source of sound is placed and at second opening the interference is observed.
iv) Place a vibrating tuning fork near end A and hear the sound at end C.
v) The sound waves travel through tube along path ABC and ADC.
vi) The wave reaching the point C is resultant of two waves.
vii) The intensity of wave at C depends on the path difference x = ADC – ABC.
i.e.
; for maximum sound
and
; for minimum sound
viii) Also when the tube D1 is gradually slid inwards or outwards, the change of intensity can be observed and positions of maximum and minimum can be noticed at regular interval of time.
ix) Let for the position of D1, the intensity of sound is maximum.
x) On moving the tube by a distance
, the intensity of sound changes to a minimum and moving the tube by 
the intensity remains maximum.
ii) The tube D2 has two openings.
iii) At one opening a source of sound is placed and at second opening the interference is observed.
iv) Place a vibrating tuning fork near end A and hear the sound at end C.
v) The sound waves travel through tube along path ABC and ADC.
vi) The wave reaching the point C is resultant of two waves.
vii) The intensity of wave at C depends on the path difference x = ADC – ABC.
i.e.
; for maximum sound and
; for minimum sound viii) Also when the tube D1 is gradually slid inwards or outwards, the change of intensity can be observed and positions of maximum and minimum can be noticed at regular interval of time.
ix) Let for the position of D1, the intensity of sound is maximum.
x) On moving the tube by a distance
, the intensity of sound changes to a minimum and moving the tube by the intensity remains maximum.
