Difference Between Diffraction and Interference

Difference Between Diffraction and Interference - A Complete Guide

Edited By Vishal kumar | Updated on Sep 24, 2024 04:44 PM IST

This article includes the definition of interference and diffraction, the difference between interference and diffraction, diffraction examples; Young’s single slit experiment and Young’s double-slit experiment.
Note: Interference meaning in Tamil is குறுக்கீடு, interference meaning in Bengali is হস্তক্ষেপ, and deflection meaning in Tamil is விலகல்

JEE Main 2025: Physics Formula | Study Materials | High Scoring Topics | Preparation Guide

JEE Main 2025: Syllabus | Sample Papers | Mock Tests | PYQs | Study Plan 100 Days

NEET 2025: Syllabus | High Scoring Topics | PYQs

$Difference Between Diffraction and Interference - A Complete Guide$

Difference Between Diffraction and Interference - A Complete Guide

Interference and diffraction of light:

Huygens’s principle failed to explain the wave nature of light. In 1801, the famous physician Thomas Young with his experiment explained the wave and particle nature of light.

What is the interference of light?

By Young’s experiment, the superposition of light from the two-slit causes an interference pattern. The phenomenon of superposition of light waves is called interference of light.

Destructive interference and Constructive interference of light

Interference forms a wave having higher or lower amplitude. Hence, two types of interference of light are obtained by this experiment. They are constructive and destructive interference. When two waves overlap each other and form a wave with a higher amplitude is called constructive interference. When the waves overlap and cancel out each other then it is called destructive interference. If the phase difference between the waves is an even integral multiple i.e., 2Π, 4 Π… then constructive interference is observed whereas if the phase difference is an odd integral multiple of pi, i.e., Π, 3 Π, 5 Π, etc then it is destructive interference.

Also read -

What is the diffraction of light?

The bending of light around the narrow obstacles or openings and encroachment to the geometrical shadows is known as the diffraction of light.

$Diffraction of light$

Figure 2 Diffraction of light

Diffraction is observed in all kinds of waves such as electromagnetic waves, sound waves, water waves, etc. Fringes having light, dark, and coloured bands are produced by the diffraction of light. Diffraction gives the concept of reflection, refraction, and interference.

From Bragg’s law, the relation between the wavelength of light λ and the spacing of the crystal plane d is observed.

Bragg's law

Figure 3 Bragg's law

nλ=2dsinθ Where n is the integer and θ is the reflected angle.

Therefore, if the wavelength of light is proportional to the size of the opening, the bending of light is observed. The bending of light is visible if the opening is comparable to the wavelength of light. The bending is invisible if the opening is larger than the wavelength of light. Therefore, the direction of light depends on the wavelength of light and spacing between the slits.

Related Topics Link,

Difference between interference and diffraction

The two main phenomenons of wave optics interference and diffraction are differed by the following facts:

Interference is the wave formed from two discrete sources that resulting discrete wavefronts whereas diffraction is the secondary waves formed from discrete parts of the same wave.
In interference, the fringe width is identical while in diffraction fringe width is different.
More number of fringes is seen in interference and it is less in number in the case of diffraction.
Similar intensity is observed in all the points on maxima in the case of interference but in diffraction the intensity is variable.
In interference, a region having minimum intensity is dark as the value is close to zero. While in diffraction, intensity deviates for different positions as intensity doesn’t have zero value.
Interference sources have a maximum of two sources as reference sources while diffraction sources have more than the sources that are considered as reference sources.

JEE Main Highest Scoring Chapters & Topics

Just Study 40% Syllabus and Score upto 100%

Download E-book

In this way we can differentiate between interference and diffraction.

Also Read :

Young’s single slit experiment:

In a single slit experiment, the monochromatic light is passed through a single slit. The pattern obtained on the background is similar to the slit used. As we move away from the central maximum, the width and intensity in single slit diffraction decrease.

Young’s double-slit experiment:

In a double-slit experiment, Young showed both the particle and wave nature of light. In this, two slits are used for the monochromatic light to pass through. Then, the pattern is observed in the background. The wave nature of light is responsible for the light to travel through slits and overlap each other causing light and dark bands on the background. In his experiment, he used two coherent light sources to cause the interference of light constructively or destructively.

Types of diffraction:

There are two types of diffraction. They are,

Fresnel diffraction: Both the light source and the background screen should be at a finite distance from the slit as the incident waves are not parallel to each other.
Fraunhofer diffraction: The incident light waves are parallel and so the light source and screen are at infinite distance from each other.

NCERT Physics Notes :

Important formulas in wave optics:

Young's double-slit experiment

Figure 4 Young's double-slit experiment

Separation of n^th order bright fringe from the central fringe is,

y_n=Dnλ/d , n=1, 2, 3……

Here, D is the distance between slit and screen, λ is the wavelength of the wave, d is the distance between two slits.

Separation of n^th order bright fringe from the central fringe is,

y_n=(2n-1)Dλ/2d , n=1, 2, 3…..

Fringe width of bright and dark fringe is,

β=Dλ/d

The angular position of n^th order,

Dark fringe= y_n/D=(2n-1) λ/2d
Bright fringe= y_n/D= nλ/d for n=1, 2, 3…..

Also check-

Frequently Asked Questions (FAQs)

1. What are coherent and incoherent sources of light?

Coherent sources are the sources emitting waves with zero or constant phase difference and the same frequency. Incoherent sources have variable frequency and phase differences.

2. What are interference and diffraction class 12?

Interference is the superposition of waves that emerged from the narrow slits. Diffraction is the superposition of waves of the same wave that emerged from each point on a single slit.

3. What are the conditions for interference?

The conditions for interference are,

Light sources must be coherent sources.
To have greater contrast, the amplitude of the electric field vector of the light wave should be the same.

4. Define Snell’s law.

Snell’s law states that the ratio of the sine of angles of incidence to the sine of the angle of refraction is a constant. It is given by,

sin i/ sin r =n₁/n₂=constant=μ

Here, μ is the refractive index, i is the angle of incidence, r is the angle of refraction.

5. What is the relationship between the distance of separation between the slit and the angular separation between fringes?

θ=λ/d , where θ is the angular separation between the fringes, λ is the wavelength of the wave, d is the separation between the slit.

6. What is Brewster’s angle?

At a particular angle of incidence, an unpolarized light ray exhibits maximum polarization. This angle is called Brewster’s angle. It can be represented mathematically as,

μ=tani_p

Here, μ is the refractive index, i_p is the polarizing angle

Therefore, according to the equation, the tangent of the polarizing angle is equal to the refractive index of the medium.