Diffraction and interference are phenomena associated with the wave nature of particles. Diffraction can be plainly defined as the spreading of waves while passing through obstacles. Interference can be defined as the combination of two or more waves. In this article, we discuss 10 differences between diffraction and interference.
Difference between diffraction and interference
| Parameters | Diffraction | Interference |
| Definition | Diffraction is defined as the spreading of waves around obstacles. Diffraction also takes place with sound. | Interference is the superimposition of two waves to form a resultant wave with a greater or lesser amplitude. |
| How does it occur? | It happens because of the superposition of secondary wavelets. | It occurs due to the superposition of two waves coming from two different coherent sources. |
| Types | They are of two types: •Fresnel’s diffraction: If the source of light and the screen are kept at a finite distance from the diffracting obstacle then Fresnel’s diffraction occurs. •Fraunhofer diffraction: Fraunhofer diffraction can be observed if the source of light and the screen are both at an infinite distance from the diffracting obstacle. | They are also two types: •Constructive interference: Constructive interference is defined as the superposition of two waves to get a greater amplitude like we use speakers to get a greater amplitude of sounds. •Destructive interference: When two waves in opposite polarity or direction superimpose on each other in a way that they cancel each other, destructive interference can be observed. |
| Fringe width | Fringes are of varying width in diffraction. | The fringe widths are constant in interference. |
| Intensity of fringe | Bright fringes are of the same intensity. | The intensity of successive fringes is not the same. The intensity decreases with fringes. |
| Obstacles | Obstacles are necessary for diffraction | An obstacle is not necessary for direction. |
| Fringe spacing | Fringe spacing is non-uniform in diffraction. | Fringe spacing is non-uniform in diffraction. |
| Contrast between maxima and minima | The contrast between maxima and minima is poor | The contrast between maxima and minima is certainly good |
| Wave propagation direction | It changes after diffraction | It does not change after superposition |
| Common examples | X-ray diffraction, CD rainbow light, etc. | Light reflected from a film of oil on water, noise in a wide hall, etc. |
| Image |  Jacopo Bertolotti, CC0, via Wikimedia Commons |  And1mu, CC BY-SA 4.0 https://creativecommons.org/licenses/by-sa/4.0, via Wikimedia Commons |
