Applied Physics

Summary:

This Applied Physics note explains the concept of interference in waves, specifically in the context of thin films. Interference occurs when two waves superimpose, resulting in either constructive or destructive interference. The Principle of Superposition states that the resultant displacement of particles in a medium acted upon by two or more waves is the algebraic sum of the displacements of the same particle due to individual waves in the absence of the others. The article also describes the conditions necessary to obtain stationary interference fringes and the production of colours in thin films with monochromatic or white light

Excerpt:

Applied Physics

Interference:

When two or more waves are superimposed, then there is a modification of intensity or amplitude in the region of superposition. This modification of intensity or amplitude in the region of superposition is called Interference.

When the resultant amplitude is the sum of the amplitudes due to two waves, the interference is known as Constructive interference, and when the resultant amplitude is equal to the difference between two amplitudes, the interference is known as destructive interference.

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PRINCIPLE OF SUPERPOSITION:

This principle states that the resultant displacement of a particle in a medium acted upon by two or more waves simultaneously is the algebraic sum of displacements of the same particle due to individual waves in the absence of the others.

Consider two waves travelling simultaneously in a medium. At any point, let y1 be the displacement due to one wave and y2 be the displacement of the other wave at the same instant.

Then the resultant displacement due to the presence of both waves is given by:

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+ve Sign has to be taken when both the displacements y1 & y2 are in the same direction
−ve Sign’ has to be taken when both the displacements y1 & y2 are in the opposite direction.

INTERFERENCE IN THIN FILMS

Applied Physics