14.Waves and Sound
medium

A tuning fork of frequency $392 Hz,$ resonates with $50 cm $ length of a string under tension ($T$). If length of the string is decreased by $2\%$, keeping the tension constant, the number of beats heard when the string and the tuning fork made to vibrate simultaneously is

A

$4$

B

$6$

C

$8$

D

$12$

Solution

(c) $n \propto \frac{1}{l}$ ==> $\frac{{\Delta n}}{n} = – \frac{{\Delta l}}{l}$ 

If length is decreased by $2\%$ then frequency increases by $2\%$ i.e., $\frac{{{n_2} – {n_1}}}{{{n_1}}} = \frac{2}{{100}}$ 

==> ${n_2} – {n_1} = \frac{2}{{100}} \times {n_1} = \frac{2}{{100}} \times 392 = 7.8 \approx 8.$

Standard 11
Physics

Similar Questions

Start a Free Trial Now

Confusing about what to choose? Our team will schedule a demo shortly.