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

Four different independent waves are represented by $(i)$ $y_1 = a_1 \sin \omega t$,$(ii)$ $y_2 = a_2 \sin 2\omega t$,$(iii)$ $y_3 = a_3 \cos \omega t$,and $(iv)$ $y_4 = a_4 \sin (\omega t + \frac{\pi}{3})$. With which two waves is interference possible?

Speed of a transverse wave on a straight wire (mass $6.0\; g$,length $60\; cm$,and area of cross-section $1.0\; mm^{2}$) is $90\; ms^{-1}$. If the Young's modulus of the wire is $16 \times 10^{11}\; Nm^{-2}$,the extension of the wire over its natural length is: (in $; mm$)

$A$ stretched uniform wire of length $L$ under tension $T$ is vibrating with fundamental frequency $n$. $A$ closed pipe of the same length $L$ is also vibrating with the same fundamental frequency $n$. If the tension $T$ is increased by $16 \,N$, the wire resonates with the $2^{\text{nd}}$ harmonic of the same closed pipe. The initial tension in the wire is: (in $\,N$)

$Assertion :$ 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.

$A$ pulse shown here is reflected from the rigid wall $A$ and then from the free end $B$. The shape of the string after these $2$ reflections will be