Two small speakers are separated by a distance of 7 cm, as shown. The speakers a

Question

Two small speakers are separated by a distance of 7 cm, as shown. The speakers are driven in phase with a sine wave signal of frequency15 kHz. A small microphone is placed a distance 1.4 m away from the speakers on the axis running through the middle of the two speakers, and the microphone is then moved perpendicular to the axis. Where does the microphone record the first minimum of the interference pattern from the speakers as measured from the axis? The speed of sound in air is 343 m/s.

( ) m (from axis)

and the first maximum

( )m (from axis)

Explanation / Answer

Constructive interference condition: d*sin(theta1) = m*lamda ,m =0,1,2

Destructive interference condition:d*sin(theta2) =(m+1/2)*lamda ,m =0,1,2,

lamda= (343/15) *10^-3=0.02286

7*10^-2* sin(theta1)= 0.02286

sin(theta1)=19.067

distance from axis is L*tan(theta1)=0.483 mts-------maxima

7*10^-2* sin(theta2)= 1.5*0.02286

theta2=29.33

distance from axis is L*tan(theta2)=0.7866 mts

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