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10.3 Superposition Principle

The effect of two or more waves, on the oscillations of particles of a medium at which the waves arrive simultaneously, is given by the superposition principle.

It states that "The resultant vibration of any particle at which two or more waves arrive simultaneously is given by the Vector addition of displacements given to the particle of each wave independently of the other."

The principle is illustrated in the following diagram:


  1. The use of transverse waves is just for visual effect.

  2. If the angle subtended at P by the lines of propagations S1P and S2P of the waves is negligible, i.e. the distance between sources S1S2 is much smaller than the distance of either of the sources from 'P',then PM and PN are either parallel to each other or are anti - Parallel to each other.

  3. When   and in same direction as PM or PN. This condition is called constructive interference.

  4. When PM anti- || to PN then PQ = PM - PN or PQ = PN- PM which ever is +ve and in the direction of the greater of the two.


10.1 Intensity and Pitch
10.2 Doppler Effect
10.3 Superposition Principle
10.4 The Phenomenon of Beats of Sound
10.5 Standing or Stationary Waves
10.6 Forced Oscillations and Resonance

Chapter 11

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