If two waves of the same frequency and same amplitude,on superimposition,produce a resultant disturbance of the same amplitude,the phase difference between the waves is

Two identical coherent sound sources $R$ and $S$ with frequency $f$ are $5 \,m$ apart. An observer standing equidistant from the sources at a perpendicular distance of $12 \,m$ from the line $RS$ hears maximum sound intensity. When the observer moves parallel to the line $RS$ to a position directly in front of one of the sources,the sound intensity is a minimum. $A$ possible value of $f$ is close to ............ $Hz$ (the speed of sound is $330 \,m/s$).

Two waves with same amplitude and frequency superpose at a point. The ratio of resultant intensities when they arrive in phase to that when they arrive $90^{\circ}$ out of phase is $\left[\cos \frac{\pi}{2}=0\right]$

Two waves are simultaneously passing through a string and their equations are:
${y}_{1} = {A}_{1} \sin {k}({x} - {vt}), {y}_{2} = {A}_{2} \sin {k}({x} - {vt} + {x}_{0}).$
Given amplitudes ${A}_{1} = 12 \, {mm}$ and ${A}_{2} = 5 \, {mm}$,${x}_{0} = 3.5 \, {cm}$,and wave number ${k} = 6.28 \, {cm}^{-1}$. The amplitude of the resulting wave will be $...... \, {mm}$.

Two generators $S_1$ and $S_2$ produce water waves of equal frequency. $A$ point $P$ is located such that $(S_1P - S_2P)$ is equal to half a wavelength. When operated alone,$S_1$ produces an oscillation of amplitude $2a$ at $P$,while $S_2$ produces an oscillation of amplitude $a$. If the generators are operated in phase,which graph correctly shows the resultant oscillation at $P$?

Two waves are superimposed whose ratio of intensities is $9: 1$. The ratio of maximum and minimum intensity is