Question

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

Answer 1

The correct option is D 256 - 5 Hz

$t_1=256Hz$

For turning fork, where $f_2-f_1=\pm 5$

$f_2=$ frequency of piano

$f_2=(256+5)Hz$ or $(256-5)Hz$

When tension is increased the beat frequency decreases to $2$ beats per second. If we assume that frequency of piano string is $261Hz$. Then on increasing tension frequency, more than $261Hz$. But it is given that beat frequency decreases, therefore $261Hz$ is not post.

$\therefore (256-5)Hz$