Question

During superposition of two sound waves of nearly equal frequencies, the beat frequency is defined as the

• A. sum of frequencies of interfering waves
• B. number of times the resultant intensity becomes maximum or minimum in one second
• C. average of frequencies of interfering waves
• D. mean of square of frequencies of interfering waves

Answer 1

The correct option is B number of times the resultant intensity becomes maximum or minimum in one second

Beats are produced when two sound waves of slightly different frequencies superimpose.
The beat frequency is,
$f_b=|f_1-f_2|$, and
The beat period,
$T_b=\frac{1}{f_b}$

From the figure, we can see that, in one beat period, there is one maximum or one minimum intensity.
So, beat frequency is the number of times the resultant intensity becomes maximum or minimum in one second.