An oscillator of frequency `680 Hz` drives two speakers . The speakers are fixed on a vertical pole at a distance `3 m` from each other as shown in Fig. 7.103. A person whose height is almost the same as that of the lower speaker walks towards the lower speaker in a direction perpendicular to the pole. Assuming that there is no reflection of sound from the ground and speed of sound is `v = 340 m//s` , answer the following questions.

How far is the person from the pole when he hears a minimum in sound intensity a second time ?

Options

A. `5.6 m`
B. `7.8 m`
C. `12.4 m`
D. `17.6 m`

Answer

A

Explanation

`Delta x = (3)/(2) lambda`
`D( 1 + (9)/( D^(2)))^(1//2) - D = (lambda)/(2)`
`D = 6 m "closest" 5.6 m`