Two identical sounds $S_1$ and $S_2$ reach at a point $P$ in phase. The resultant loudness at point $P$ is $n\,\, dB$  higher than the loudness of $S_1$. The value of $n$ is

During propagation of a plane progressive mechanical wave incorrect statement is

A string of mass $100\, gm$ is clamped between two rigid support. A wave of amptitude $2\, mm$ is generated in string. If angular frequency of wave is $5000\, rad/s$ then total energy of the wave in string is ..... $J$

When a wave travels in a medium, the particle displacement is given by : $y = a\,\sin \,2\pi \left( {bt - cx} \right)$ where $a, b$ and $c$ are constants. The maximum particle velocity will be twice the wave velocity if

The apparent frequency of a sound wave as heard by an observer is $10\%$ more than the actual frequency. If the velocity of sound in air is $330\, m/sec$, then 
$(i)$ The source may be moving towards the observer with a velocity of $30\,ms^{-1}$
$(ii)$ The source may be moving towards the observer with a velocity of $33\,ms^{-1}$
$(iii)$ The observer may be moving towards the source with a velocity of $30\,ms^{-1}$
$(iv)$ The observer may be moving towards the source with a velocity of $33\,ms^{-1}$

A cylindrical tube $(L = 120\, cm.)$ is resonant with a tuning fork of frequency $330\, Hz$. If it is filling by water then to get resonance again, minimum length of water column is  ...... $cm$  $(v_{air} = 330\, m/s)$