Question

Two longitudinal sinusoidal pressure waves, one having lower frequency of $2Hz$ and both travelling in same direction through the same medium as shown in the figure are superimposed. Then beat frequency detected by a detector as a result of the superposition is:

• A. $1Hz$
• B. $2Hz$
• C. $3Hz$
• D. $4Hz$

Answer 1

The correct option is D $4Hz$

$\frac{f_1}{f_2}=\frac{V/2l}{V/6l}=3$

$\Rightarrow$ $f_1=3f_2=6Hz$ ..... $(\because f_2=2Hz)$

$\Rightarrow$ beat frequency $=f_1-f_2=6-2=4Hz$