Question

A tuning fork of frequency $200 \, Hz$ is in unison with a sonometer wire. Tension in the wire of sonometer is increased by $1\%$ without any change in its length. Find the number of beats heard in $9 \, s$ .

• A. $9$
• B. $3$
• C. $6$
• D. $12$

Answer 1

Answer: (A)

$f=\frac{1}{2 \pi }\sqrt{\frac{T}{\mu }}$
$\frac{\Delta f}{f}=\frac{1}{2}\frac{∆T}{T}$
$\Delta f=\frac{1}{2}\times \frac{1}{100}\times 200$
$\Delta f=1$
Beat frequency = 1
Number of beats in 9 second $=9\times 1=9$