Question

Two loud speakers L${}_1$and L${}_2$ , driven by a common oscillator and amplifier, are arranged as shown. The frequency of the oscillator is gradually increased from zero and the detector at D records a series of maxima and minima. If the speed of sound is 330 m/s then the frequency at which the first maximum is observed is :

• A. 165 Hz
• B. 330 Hz
• C. 495 Hz
• D. 660 Hz

Answer 1

The correct option is B 330 Hz

$L_{1}D=40m$

$L_{2}D=\sqrt{(40{)}^2+(9{)}^2}=\sqrt{1681}=41m$

$L_{2}D-L_{1}D=1m$

$\therefore$ first maximum occurs when $\lambda =L_{2}D-L_{1}D$

$\Rightarrow \frac{v}{\phi }=1m$

$f=v=330Hz$