A sound wave of wavelength 32 cm enters the tube at S as shown in the figure. Then the smallest radius r so that a minimum of sound is heard at detector D is

Options

A. 7 cm
B. 14 cm
C. 21 cm
D. 28 cm

Answer

B

Explanation

Path difference `= pi r - 2r`
The path difference for minimum sound is `(lamda)/(2)`,
`(lamda)/(2) = r [pi -2]`
`16 = r xx ((22)/(7) - 2)`
`16 = r xx ((22 - 14)/(7))`
`16 = r xx (8)/(7)`
`r = 2 xx 7 = 14m`