**The Principle Of Superposition states that when two waves of the same kind meet at a point in space, the resultant displacement at that point is the vector sum of the displacements that the two waves would separately produce at that point.**

Interference refers to the superposing of two or more coherent waves to produce regions of maxima and minima in space, according to the principle of superposition.

Constructive interference occurs when two or more waves arrive at the screen in phase with each other, such that the amplitude of the resultant wave is the sum of the amplitude of the individual waves.

Destructive interference occurs when the two or more waves arrive $\pi$ out of phase with each other.

- Resultant wave has minimum amplitude.

Phase difference between the waves at P | |
---|---|

Constructive interference | n ($2 \pi$) |

Destructive interference | (n + $\frac{1}{2}$) 2$\pi$ |

Path difference | ||
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2 sources in phase | 2 sources $\pi$ out of phase | |

Constructive interference | n$\lambda$ or 0 | (n + $\frac{1}{2}$)$\lambda$ |

Destructive interference | (n + $\frac{1}{2}$)$\lambda$ | n$\lambda$ or 0 |