Question

A fork $P$ of unknown frequency gives six beats per second when sounded with another fork $Q$ of frequency $260\text{Hz}$. The fork $P$ is now loaded with a piece of wax and again six beats per second is heard, then frequency of fork $P$ is

• A. $260\text{Hz}$
• B. $254\text{Hz}$
• C. $266\text{Hz}$
• D. $250\text{Hz}$

Answer 1

The correct option is C $266\text{Hz}$

Beats frequency $=f_P-f_Q$
$f_P-260=\pm 6$
$f_P=260\pm 6$
Thus possible frequency of fork $P$ are $260\pm 6=266\text{Hz or}254\text{Hz}$,
As frequency decreases on loading, therefore original frequency of fork $P$ is $266\text{Hz}$.