Sound waves

Question 1

Why does the sound exiting the Quinche’s tube vary as the movable tube is slow pulled out?

Answer 1

• initially the path difference is 0, resultant displacement is at its maximum
• as the movable object is moved out, path difference increases, the waves are no longer in phase and displacement and loudness decreases
• When path difference is half the wavelength, the two are in aniphase and the sound is at its quitest
• as the path difference continues to increase, the two waves become more in phase and the sound gets louder

Question 2

What is the equation for the minimum distance moved for the sound detectede to be detected at its quitest?

Answer 2

path difference = 2 (d₂ - d₁) = 2 (distance moved by moveable tube) = one half wavelength

distance moved by moveable tube = path difference / 2