A point source emits sound equally in all directions in a non-absorbing medium. Two points $P$ and $Q$ are at a distance of $9$ meters and $25$ meters respectively from the source. The ratio of the amplitudes of the waves at $P$ and $Q$ is

If $L_1$ and $L_2$ are the lengths of the first and second resonating air columns in a resonance tube, then the wavelength of the note produced is

The phase difference corresponding to path difference of $x$ is

Two waves represented by

$y_1 = 10\,sin\,(2000\,\pi t + 2x)$

and ${y_2} = 10{\mkern 1mu} \,sin\,{\mkern 1mu} \left( {2000{\mkern 1mu} \pi t + 2x + \frac{\pi }{2}} \right)$ are superposed at any point at a particular instant. The resultant amplitude is ..... $unit$

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

A sound absorber attenuates the sound level by $20\, dB$. The intensity decreases by a factor of