Two superimposing waves are represented by the equations $y_1 = 2 \sin 2 \pi(10 t - 0.4 x)$ and $y_2 = 4 \sin 2 \pi(20 t - 0.8 x)$. The ratio of $I_{\max}$ to $I_{\min}$ is ........

Which of the following statements is incorrect?

Fill in the blanks:
$(i)$ For humans,the minimum wavelength of a sound wave in the audible range is nearly ...... .
$(ii)$ Only ...... waves can be propagated by a fluid medium.
$(iii)$ The distance travelled by a travelling wave having wavelength $\lambda$ and periodic time $T$,in one second is ...... .

$Assertion :$ Sound waves cannot travel in vacuum but light can travel in vacuum.
$Reason :$ Sound waves are longitudinal waves and they cannot be polarised but electromagnetic waves are transverse and they can be polarised.

Two speakers connected to the same source of fixed frequency are placed $2.0 \ m$ apart in a box. $A$ sensitive microphone placed at a distance of $4.0 \ m$ from their midpoint along the perpendicular bisector shows maximum response. The box is slowly rotated until the speakers are in line with the microphone. The distance between the midpoint of the speakers and the microphone remains unchanged. Exactly five maximum responses are observed in the microphone in doing this. The wavelength of the sound wave is .... $m$

$A$ clamped string is oscillating in the $n^{th}$ harmonic,then