$A$ 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 ... $m$.

If the separation between the screen and the source is increased by $2\%$,what would be the effect on the intensity?

$A$ stationary point source of sound emits sound uniformly in all directions in a non-absorbing medium. Two points $P$ and $Q$ are at a distance of $4 \ m$ and $9 \ m$ respectively from the source. The ratio of amplitudes of the waves at $P$ and $Q$ is

$A$ point source emits sound equally in all directions in a non-absorbing medium. Two points $P$ and $Q$ are at distances of $2 \ m$ and $3 \ m$ respectively from the source. The ratio of the intensities of the waves at $P$ and $Q$ is:

$A$ 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.

Two waves represented by the following equations are travelling in the same medium: $y_1 = 5\sin 2\pi (75t - 0.25x)$ and $y_2 = 10\sin 2\pi (150t - 0.50x)$. The intensity ratio $I_1/I_2$ of the two waves is: