Sunday, January 3, 2010



The Principle of Superposition states that when two or more waves meet at a point simultaneously, the resultant displacement at that point is the vector sum of the displacements produced at that point by each of the wave separately.

Diffraction is a phenomenon by which the wavefront of a propagating wave is spread out as a result of passing through an aperture or bend around an obstacle, whose size is approximately the same as the wavelength of the wave.

The extent of the spreading or bending of the wave depends on how the width of the gap or size of the obstacle compares to the wavelength of the wave.

Interference occurs when two or more waves overlap or intersect in the same region of space. To conclude whether the waves reaching a point interfere constructively or destructively depends on the phase difference of the overlapping waves at the point.

Phase is a description of the stage that a periodic motion has reached, usually by comparison with another such motion of the same frequency. Two varying quantities are said to be in phase if their maximum and minimum values occur at the same instants; otherwise, there is said to be a phase difference (phase angle).

Coherent sources are sources which produce waves of the same frequency with a constant phase difference.

For the characteristic pattern of regular bright fringes interspersed with dark fringes to be observed,
• the sources must be coherent
• the overlapping waves have the same or almost equal amplitude
• for transverse waves, they must be either unpolarised or polarised in the same plane

A stationary wave is set up as a result of the superposition of two progressive waves
of the same amplitude and frequency travelling at the same speed in opposite directions.

Nodes are points in a stationary wave where the amplitude is zero.

Antinodes are point in a stationary wave where the amplitude is a maximum.
Stationary wave is a form of wave in which the profile of the wave does not move through the medium but remains stationary. This is in contrast to the progressive wave, in which the profile moves through the medium at the speed of the wave.

A taut string or a column of air oscillates at numerous frequencies simultaneously. At these resonant frequencies, waves travel in both directions along the string or air column, reinforcing and cancelling each other to form stationary waves. Because of the typical spacing of the resonances, these frequencies are mostly limited to integer multiples, or harmonics, of the lowest frequency. The lowest frequency harmonic is called the fundamental and the others are called overtones.


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