Question

Column I represents the description of a sound wave or snapshot and Column II represents variation of some quantities. Match Column I with Column II.

• A. A – p, B – q, C – p, D – s
• B. A – q, B – q, C – q, D – s
• C. A – q, B – p, C – q, D – q
• D. A – q, B – s, C – p, D – s

Answer 1

The correct option is B A – q, B – q, C – q, D – s

For (A) and (B), pressure at open end will be equal to atmospheric pressure and hence there will be a pressure node at A while point B will have a displacement node.

(It is important to realize that there is a difference between the nodes and the antinodes of the molecular displacement and of the air pressure. Traditionally, the term node is used for the position where the molecules do not move, i.e. a displacement node. The displacement is 90 degrees out of phase with the air pressure. This means that where a displacement node is found, you will also have a pressure antinode – and vice versa.)

Similarly (C) in Column I has B as node position.


Now we know that at displacement node, potential energy is maximum because of the maxmimum elongation. Hence (A), (B) and (C) will match to (q) in Column II.

Similarly position B in (D) of Column 1 is an antinode position where acceleration is maximum, kinetic energy is zero at that instant because speed is zero. Similarly potential energy will also be zero because there will be zero deformation at that particular moment.