What are Incoherent Sources?

Incoherent sources are those that produce waves with no fixed phase relationship between them. This implies that the waves are in different phases and their crests and troughs are not always in alignment. Incoherent sources may be tought of as waves that are ‘out of phase’ from each other. Waves coming from incoherent sources have multiple frequencies, amplitudes, and propagation directions. Such waves are not ‘monochromatic’.

Another notable point is that the waves lack spatial as well as temporal correlation which tells that there is no fixed connection between them in space and time. Typical examples of the incoherent sources are all natural light that we get, such as the sun, the incandescent bulbs and the fluorescent lamps.

Scattering of Light

When the light interacts with a rough or irregular surface, it can be scattered in different directions. The ray can be scattered either coherently or incoherently determined by the surface property and light wavelength. The coherent scattering happens on the surfaces that are smooth and regular, with a wavelength of light much larger than the surface irregularities. Here, the light which is scattered have a fixed phase relationship with the incident light so the interference patterns can be observed.

If roughness and irregularities on the surface are roughly the same as the light’s wavelength, incoherent scattering does take place. In this case, the scattered light will have random phase, and no interference pattern would be observed.

Also Read: Scattering of Light

Constructive Interference

The constructive interference happens when the two waves that are propagating in the same direction, with the similar phase and the same frequency, superimpose to result in a wave with a larger amplitude. This takes place when the wave crests and troughs all are in the same line.

Destructive Interference

When two or more waves of the same frequency but with opposite phases come together, their destructive interference occurs and as a result of their addition, a wave of less amplitude or even their complete cancellation is produced. These are often observed when the crests of one wave match the troughs of others.

Locus Point

The locus point is the location in space where waves from two or more coherent sources meet constructively or destructively to form an interference pattern. The location of the locus point is based on the relative phase and amplitude of the waves.

Coherent and Incoherent addition of waves are used in various fields of physics like acoustics, optics, and quantum mechanics. The waves adding up with each other can interfere either constructively or destructively, depending upon their phase differences and amplitudes. This phenomenon is known as the superposition of waves, which results from the coherent or incoherent addition of waves.