Question

A fork A has frequency 2% more than the standard fork and B has a frequency 3% less than the frequency of same standard fork. The forks A and B when sounded together produced 6 beats/s. The frequency of fork A is

• A. 116.4 Hz
• B. 120 Hz
• C. 122.4 Hz
• D. 238.8 Hz

Answer 1

Answer: (C)

The frequency of A
$n_A=n+\frac{2}{100}n$
and the frequency of B
$n_B=n-\frac{3}{100}n$
According to question
$n_A-n_B=6$
$(n+\frac{2}{100}n)-(n-\frac{3}{100}n)=6$
or $\frac{5}{100}n=6$
$\Rightarrow n=\frac{600}{5}=120Hz$
The frequency of A
$n_A=(n+\frac{2}{100}n)=120+\frac{2}{100}\times 120$
$=122.4Hz$