The intensity level at a distance of $200 \ cm$ from a sound source is $80 \ dB$. If there is no loss of acoustic power in the air and the threshold intensity of hearing is $10^{-12} \ W/m^2$,what is the intensity level at a distance of $400 \ cm$ from the source (in $dB$)?

As a wave propagates,which of the following statements is correct?

$A$ 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?

Which of the following statements is correct?

$A$ 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 $A$)

As a wave propagates: