Question 3: Explain the following terms;

(1) Crest (2) Trough (3) Compression (4) Rarefaction (5) Node (6) Anti-node

In case of a transverse wave, the particles of the medium vibrate up and down about their mean position as the wave passes through them. So, in this process some of the medium particles are above their mean position and some are below the mean position.

### Crest

A crest is the portion of the wave above the mean level of the medium.

### Trough

A trough is the portion of the wave below the mean level of the medium.

When a longitudinal wave passes through the medium, the particles of the medium vibrate about their mean positions along the direction of motion of the wave. As a result, parts of the medium are overcrowded and parts are less crowded.

### Compression

Part of the medium where the particles overcrowd during the motion of a longitudinal wave is called compression.

### Rarefaction

Part of the medium where its particles are less crowded during the motion of a longitudinal wave is called rarefaction.

### Nodes

Standing waves consist of alternate nodes and anti-nodes.

Nodes are points on a standing wave where the amplitude of oscillation of the particles of the medium is zero. They are represented by N1,N2, N3, etc.

### Anti-nodes

Between two consecutive nodes, there is a point on the standing wave where the amplitude of vibration of the particles is maximum. This point is called anti-node. All such points are represented by A1,A2, A3, etc.