The figure shows a snapshot of a travelling sine wave along a string. Four elemental portions $a, b, c,$ and $d$ are indicated on the string. Which elemental portion$(s)$ has/have the maximum potential energy?

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 $dB$)?

The clocktower ("ghantaghar") of Dehradun is famous for the sound of its bell, which can be heard, albeit faintly, up to the outskirts of the city $8 \,km$ away. Let the intensity of this faint sound be $30 \,dB$. The clock is situated $80 \,m$ high. The intensity at the base of the tower is ............. $\,dB$.

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:

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

Which property distinguishes progressive waves from stationary waves?