$Assertion :$ 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.

$A$ narrow tube is bent in the form of a circle of radius $R,$ as shown in the figure. Two small holes $S$ and $D$ are made in the tube at positions at a right angle to each other. $A$ source placed at $S$ generates a wave of intensity $I_0$ which is equally divided into two parts: one part travels along the longer path,while the other travels along the shorter path. Both the waves meet at the point $D$ where a detector is placed. If a minimum is formed at the detector,then the magnitude of the wavelength $\lambda$ of the wave produced is given by:

Match the following List-$I$ with List-$II$.

List-$I$	List-$II$
$(A)$ Transverse wave	$(i)$ Vibrations parallel to the direction of propagation
$(B)$ Longitudinal wave	$(ii)$ Vibrations perpendicular to the direction of propagation
$(C)$ Beats	$(iii)$ Superposition of waves travelling in the opposite directions
$(D)$ Stationary waves	$(iv)$ Superposition of waves travelling in same direction

The correct answer is

$A$ vibrating string of length $\ell$ under a tension $T$ resonates with a mode corresponding to the first overtone (third harmonic) of an air column of length $75 \,cm$ inside a tube closed at one end. The string also generates $4$ beats per second when excited along with a tuning fork of frequency $n$. Now, when the tension of the string is slightly increased, the number of beats reduces to $2$ per second. Assuming the velocity of sound in air to be $340 \,m/s$, the frequency $n$ of the tuning fork in $Hz$ is:

In Quincke's tube,a detector detects minimum intensity. Now,one of the tubes is displaced by $5 \, cm$. During displacement,the detector detects maximum intensity $10$ times,and finally a minimum intensity (when displacement is complete). The wavelength of sound is .... $cm$.

Two periodic waves of intensities $I_1$ and $I_2$ pass through a region at the same time in the same direction. The sum of the maximum and minimum intensities is