### Principle of Superposition

The principle of superposition states that where two or more waves meet, the total displacement at any point is the vector sum of the displacements that each individual wave would cause at that point.

#### Coherent Wave

Two wave sources which are coherent have same frequency or have constant phase difference.

### Interference

- The effect of superposition of two coherent waves is interference.
- Interference is a phenomenon of wave caused by the superposition of 2 or more coherent waves.
- The effect of interference can be studied using a ripple tank. Two dippers are used to produce two sources of coherent waves.
- Figure 3 shows the interference pattern observed.
- Interference can be constructive or destructive.

#### Constructive Interference and Anti-node

- In the interference of 2 waves, there are places where the 2 waves are always in phase (same phase) and the superposition of the waves produces oscillation with maximum amplitude. This is called the constructive interference.
- A place where constructive interference occurs is called the anti-node.

#### Destructive Interference and Node

- In the interference of 2 waves, there are also places where the 2 waves are always anti-phase (phase difference = 180°) and the superposition of the waves produces oscillation with minimum amplitude. This is called the destructive interference.
- A place where destructive interference occurs is called the node.