Assertion: No Doppler effect will be observed in sound when source and observer are moving with the same speed.

Reason: Doppler effect may be due to change in wavelength also.

Assertion: Ultrasonic is the acoustic analogue of ultraviolet radiation.

Reason: Ultraviolet rays do not produce visual sensations while ultrasonic waves are not heard by the human ear.

Assertion: Longitudinal waves are called pressure waves.

Reason: Propagation of longitudinal waves through a medium involves changes in pressure.

Assertion: If two people talk simultaneously and each creates a sound level of $60 \mathrm{dB}$ at a point $P$, then total sound level at the point $P$ is $120 \mathrm{dB}$.

Reason: Sound level is defined on a non-linear scale.

Assertion: Doppler effect does not depend upon the distance between source and observer.

Reason: If source and observer are moving with same velocities, then no Doppler effect will be observed.

Assertion: Speed of sound in ${\mathrm{O}}_2$ gas at temperature $T$ is $v$. If temperature is increased to $2T$, the molecular oxygen breaks into atomic oxygen. Then, the speed of sound under these conditions will become $2v$.

Reason: With the increase in humidity in the air, speed of sound increases.

Assertion: Fundamental frequency of a narrow organ pipe is more than a broad diameter organ pipe of the same length.

Reason: If we apply Laplace end correction, then the fundamental frequency of a closed organ pipe is more than $\frac{v}{4l}$.

Assertion: If a stretched wire fixed at both ends is vibrating in its second overtone mode, then the total number of nodes and antinodes are four each.

Reason: Number of antinodes is equal to the number of loops.

Assertion: Transverse waves cannot travel in the gaseous medium.

Reason: Gaseous medium does not have a modulus of rigidity.