`S_(1)`: Source and observer both are stationary and wind is blowing in a direction from source to observer then observer detects an apparent increase in frequency.
`S_(2)`: Beat frequency is defined as the difference of frequency of two sources.
`S_(3)`: Pressure node is always a displacement node and pressure antinode is always a displacement antinode.

Options

A. If both assertion and reason are true and reason is the correct explanation of assertion.
B. If both assertion and reason are true but reason is not the correct explanation of assertion.
C. If assertion is true but reason is false.
D. If both assertion and reason are false.

Answer

B

Explanation

At the point where a compression and a rarefaction meet, the displacement is minimum and it is called displacement node. At this point, the pressure difference is maximum, that is at same time, it is a pressure antinode. On the other hand, at the mid-point of a compression or a rarefaction, the displacement variation is maximum. Such a point is displacement antinode. However such a point is pressure node, as pressure variation is minimum at such a point.