Question

A tuning fork of known frequency 256 Hz makes 5 beats per second with the vibrating string of a piano. The beat frequency decreases to 2 beats per second when the tension in the piano string is slightly increased. The frequency of the piano string before increasing the tension was

• A. (256+2) Hz
• B. (256-2) Hz
• C. (256-5) Hz
• D. (256+5) Hz

Answer 1

Answer: (C)

(256-5) Hz

Answer 2

$t _{1}= 2 5 6 H z$ For turning fork, where $f _{2}- f _{1}=\pm 5$ $f _{2}=$ frequency of piano $f _{2}=( 2 5 6 + 5 ) H z$ or $( 2 5 6 - 5 ) H z$ When tension is increased the beat frequency decreases to 2 beats per second. If we assume that frequency of piano string is $261 Hz$. Then on increasing tension frequency, more than $261 Hz$. But it is given that beat frequency decreases, therefore $261 Hz$ is not post. $\therefore( 2 5 6 - 5 ) H z$