$A$ 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 ... $m$.

There is a long linear source of sound whose power is $P$ and length is $L$. At point $A$,the sound level is $80 \ dB$. Then at point $B$,the sound level will be .... $dB$.

$A$ musical instrument $X$ produces sound waves of frequency $n$ and amplitude $A$. Another musical instrument $Y$ produces sound waves of frequency $\frac{n}{3}$. The waves produced by $X$ and $Y$ have equal energies. The amplitude of waves produced by $Y$ will be (in $A$)

$A$ surface of area $S$ is placed perpendicular to the direction of travel of a plane wave. The energy per unit time intercepted by the surface is $E$ when the amplitude of the wave is $A$. The area of the surface is reduced to $\frac{1}{2} S$ and the amplitude of the wave is increased to $2A$. What is the energy per unit time intercepted by this smaller surface?

The 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

The displacement-time graphs for two sound waves $A$ and $B$ are shown in the figure. The ratio of their intensities $I_A/I_B$ is equal to: