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?

$A$ travelling wave is partly reflected and partly transmitted from a rigid boundary. Let $a_i, a_r$ and $a_t$ be the amplitudes of the incident wave,reflected wave,and transmitted wave,and $I_i, I_r$ and $I_t$ be the corresponding intensities. Choose the correct alternative.

$A$ point source is emitting sound waves of intensity $16 \times 10^{-8} \text{ W m}^{-2}$ at a distance of $1 \text{ m}$ from the source. The difference in intensity (magnitude only) at two points located at distances of $2 \text{ m}$ and $4 \text{ m}$ from the source respectively will be . . . . . . $\times 10^{-8} \text{ W m}^{-2}$.

As a wave propagates:

The amplitudes of two waves are in the ratio $5 : 2$. If all other conditions for the two waves are the same,what is the ratio of their energy densities?

If the ratio of the amplitude of two waves is $4 : 3$,then the ratio of their maximum and minimum intensity will be: