Difference Between Interference and Diffraction

What is Interference?

The wave-like nature of light is because the light is emitted by moving particles, and the interference and diffraction of light are due to the wave-like nature of light.  Waves can be either transverse or longitudinal. Transverse waves are waves in which the disturbance is perpendicular to the direction of propagation.

In contrast, longitudinal waves are waves in which the disturbance is parallel to the direction of propagation. Waves can be either mechanical or electromagnetic. Mechanical waves, such as sound waves, require a medium to travel, while electromagnetic waves, such as light waves, do not. Additionally, the interference shapes the medium in a specific way.

Furthermore, this shape results from the combined impact of two distinct waves on the particles of the medium. The wave-like nature of light is the result of the wave-particle duality of light. Light can exhibit wave-like and particle-like behavior, depending on the experiment being performed.

Interference occurs when two or more waves meet while traveling through the same medium. The waves combine to create a new wave with a different amplitude and phase than the individual waves.

What is Diffraction?

The term “diffraction” refers to how waves disperse when they meet a slope. That would be significant if the barrier or aperture had linear dimensions close to the incident wave’s wavelength. It also happens when the traveling wavelength is partially obstructed.

The spreading of light as it encounters a barrier is known as diffraction. On the opposite side, a pattern is produced as the light waves deflect around the obstruction. The light’s wavelength and the obstruction’s size affect how much bending occurs.

A periodic optical element called a diffraction grating splits and diffracts light into many beams that go in various directions. The wavelength of the light and the space between the grating components determine the directions of these beams. It is claimed that the beams are dispersed. Diffraction gratings are used in lasers to double light frequency and divide it into its many wavelengths.

There are many real-life situations where diffraction, or the spreading and bending of waves around objects, is essential. For example, the reddening of the setting sun and the ability to see distant objects near the horizon are both caused by the diffraction of sea waves.

As wavefronts radiate away from a point source, like a lighthouse, the distance between the wavefronts and the source gets smaller. As the waves move farther from the source, their wavelength also lengthens.

Difference Between Interference and Diffraction

The primary distinction between interference and diffraction is that although diffraction always uses one wave, interference always uses two or more.

When two waves meet and produce a new wave, interference occurs. When a wave strikes an obstruction and bends around it, diffraction begins. This is because while in the case of diffraction, the wave bends around the obstruction, in the case of interference, the waves combine to generate a new wave.

The fact that the waves involved in these processes are of different kinds separates diffraction from interference. While secondary wavelets that begin from the same wave but occur from separate areas cause the phenomena known as diffraction, interference is a feature produced by waves from two independent coherent sources.

Both have a similar sound, yet their natures are very different. It can be helpful to understand how well a telescope and a microscope can resolve objects.

Comparison Between Interference and Diffraction

Parameter of ComparisonInterferenceDiffraction  
BasicsTakes place because of the superposition of light waves from two sources.Occurs because of secondary wavelets being superimposed
Edge IntensitySameNot same  
Size of the fringesEqualUnequal  
Area splitUniformNon-Uniform  
BarriersNot requiredRequired  
Direction in which waves travelIf superposed, remains unchanged.Changes if diffracted


  1. https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.74.3600
  2. https://aapt.scitation.org/doi/abs/10.1119/1.19083