Two vibrating tuning forks produce waves given by ${y_1} = 4\sin 500\pi t$ and ${y_2} = 2\sin 506\pi t.$  Number of beats produced per minute is

Which of the following is correct ?

A person speaking normally produces a sound intensity of $40\, dB$ at a distance of $1\, m$. If the threshold intensity for reasonable audibility is $20\,dB$, the maximum distance at which he can be heard clearly is ..... $m$

The transverse displacement of a string (clamped at its both ends) is given by $y(x,t) = 0.06$ $sin\, (2\pi x /3)\, cos\, (120\, \pi t)$. All the points on the string between two consecutive nodes vibrate with

The length of open organ pipe is $L$ and fundamental frequency is $f$. Now it is immersed into water upto half of its length now the frequency of organ pipe will be

Dependence of disturbances due to two waves on time is shown in the figure. The ratio of their intensities $I_1 / I_2$ will be