Question

When tuning forks $A$ and $B$ are sounded together, $5$ beats per second are heard. The frequency of $A$ is $250\text{Hz}$. On loading fork $A$ with wax, $2$ beats per second are produced with fork $B$. The frequency of fork $B$ is -

• A. $255\text{Hz}$
• B. $320\text{Hz}$
• C. $245\text{Hz}$
• D. $420\text{Hz}$

Answer 1

The correct option is C $245\text{Hz}$

Given :

Initial frequency of tuning fork $A$, $f_A=250\text{Hz}$
Number of beats per second $=5$

$\therefore |f_A-f_B|=5\text{Hz}$.

After loading fork $A$ with wax, the frequency of fork $A$ will decrease.

Now, number of beats per second $=2$

Since, the number of beats per second decreases with the decrease in frequency of fork $A$.

$\therefore f_A-f_B=5\text{Hz}$

$\Rightarrow f_B=f_A-5=250-5=245\text{Hz}$