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Difference Between Diffraction and Interference

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Last updated date: 29th Feb 2024
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What are the Applications of Diffraction and Interference in Technology?

The law of diffraction is quite helpful in manufacturing and designing modern technological appliances or instruments that can help researchers to determine the characteristics of a particular material. There are crystals available in our nature and the molecular construction of the crystals can vary as well. There are simple crystals that diffract X-rays due to the atomic positions as in the case of simple crystals, the planes of atoms are equally spaced. It has been proven by Bragg's law. 


Researchers have invented a particular kind of instrument that is named a diffractometer that is based on the concept of diffraction. This particular instrument can produce diffraction patterns with the help of X-ray diffraction and it is used to compare different kinds of crystals in order to determine and find out the different molecular structures of different types of crystals.


The concept of interference is widely used in different kinds of optical testing. This concept is particularly used to test the surface quality. Some practical applications of this concept can also be mentioned here. The concept of interference is used when it comes to retrieving images from devices like telescopes and measuring the intensity of lights.


When a train passes through the tunnel, the headlight of the engine spreads around and we see darkness all around, do you know why this happens? This happens because of diffraction. 

 

Diffraction is the spreading of light in the dark areas when it passes through a narrow lane or an area and this is accompanied by interference between the waveforms produced. So, what interference is? Interference is the combination of two or more electromagnetic waveforms that form a resultant wave in which the displacement is either reinforced or canceled.

 

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Interference

Interference is the phenomenon that takes place when the meeting of the two waves takes place as they travel along with the same medium. Besides this, the interference causes the medium to take a particular shape or orientation. Moreover, this shape is due to the whole or the net effect of two individual waves on the medium’s particles.

 

Diffraction

Diffraction happens due to the spreading out of waves passing through an aperture. In the case of diffraction, the size of the obstacle or aperture is of similar straight dimensions to the incident wave’s wavelength, and its occurrence is significant. Furthermore, it takes place when the traveling wavelength’s part gets obscured or shaded.

 

Distinguish Between Interference and Diffraction 

Now, let us find the difference between interference and diffraction in tabular form:

Interference 

Diffraction

Interference happens because of the superposition or overlapping of two waveforms coming from two different coherent sources. 

Diffraction happens because of the superposition of secondary wavelets from the different parts of the wavefront.

The fringe width in interference is generally constant. 

Fringes are of varying width in diffraction.

We also find that bright fringes are of the same intensity.

Intensity falls quickly.

It means that in a diffraction pattern, the intensity of successive fringes goes on decreasing.

It means in an interference pattern, the number of bright fringes have the same magnitude of intensity.

This means that diffraction fringes are wide near the obstacle and their width goes on decreasing while approaching the shadow side. 

All the maxima in interference have the same magnitude of intensity.

The maxima may have a varying magnitude of maxima.

We find a good contrast between maxima and minima in interference.

A poor contrast is found between maxima and minima in the case of diffraction.

We find that there are a large number of fringes in interference. 

There are fewer fringes in diffraction.

In an interference pattern, the intensity at minima is usually very small or close to zero, which means minima is usually dark. 

Also, there is a very good contrast between the dark and bright fringe.

In a diffraction pattern, we find that the intensity of minima is never zero, and there is poor contrast between a dark and the bright fringe or fringes.

 

So, the above table clearly explains the difference between interference and diffraction in Physics. Now, let us differentiate between interference and diffraction of light:

 

Comparison Between Interference and Diffraction

Interference 

Diffraction

Interference is the spreading of waves behind obstacles. 

Diffraction is a phenomenon in which certain points of the space of wave oscillations are amplified while others are annulled or attuned.  

Waves in an interference pattern stay away from the original route in the same elastic environment. 

Superposition of waves occurs in the same material environment. 

The dimensions of cracks or obstacles should be of the same length. 

There is a constant phase difference between the waves that is the reason these waves are called coherent waves. We consider coherent waves in the diffraction patterns. 

The direction of wave propagation never changes after superposition.

The direction of wave propagation never changes after diffraction.

An obstacle or slit is not necessary for interference. 

An obstacle or slit is necessary for interference.

Fringe spacing is uniform in interference. 

Fringe spacing is non-uniform in diffraction.

FAQs on Difference Between Diffraction and Interference

1. What is the Basic Difference Between Diffraction and Interference in Physics?

The difference between interference and diffraction of light is important to understand in Physics. The basic difference is that diffraction occurs when waves encounter an obstacle while interference occurs when two waves meet each other.


A light that passes through the edges of opaque bodies or through narrow openings and in which the rays appear to be deflected is diffraction, while interference can be seen in two sound waves meeting each other and makes it hard to distinguish between the two.

2. Describe the Two Categories of Interference.

The two categories of interference are as follows:

  • Constructive interference 

  • Destructive interference. 


Constructive interference happens only when the two superposing waves bear the same phase and amplitude. On the other hand, destructive interference takes place when the two superposing waves belong to different phases or have a phase difference but their amplitude of these waves remains the same.

3. Describe a Real-life Example of Diffraction and Interference.

Diffraction:

A solar or lunar Corona and the light passing through the hole of a dark room is diffraction.


Interference: 

A thin film of light that we see on the oil drop and soap bubble is because of the interference. 

4. Can diffraction and interference happen at the same time?

Interference can happen when the same kinds of two waves overlap each other and that results in a resultant wave that can be greater, lower or it can be of the same aptitude. Diffraction suggests the curvature of a particular wave around the corner of a particular obstacle or object. Since one particular aperture can have multiple edges and the distances between those ages can also vary. That is why interference can happen along with diffraction because the distances between the multiple edges of the particular aperture can be longer than the wavelength and interference takes place when two different types of waves wavelength overlap. 


Another example can also be mentioned here where interference and diffraction take place simultaneously. If the light source from where the light is emitting is not constant and it is constantly changing its shape, interference and diffraction can take place at the same time there also. For example, if you can consider a light source that is non-parallel and is not constant, then there is a chance that interference and diffraction will take place at once. 


But there is no reason to assume that interference and diffraction will occur at the same time because there are instances that can explain the different time periods of the occurrence of interference and diffraction. In the case of a natural phenomenon where two different wavelengths of light can interfere with each other, interference can happen there without diffraction. If you can consider the example of thin-film interference, it will be easier to understand the concept of how interference takes place without the occurrence of diffraction. 


This particular example can be considered a natural phenomenon where the light waves are reflected by the boundaries of the thin film. Due to the overlapping of the reflected lights because of the upper and lower boundaries of the thin film, interference happens. Due to the interference, the wavelength of the reflected light can be enhanced or reduced. Diffraction doesn't take place year because of the absence of multiple edges of the aperture.

5. Why is learning the concept of diffraction and interference important?

Due to the occurrence of diffraction, a beam of light with various wavelengths can be dispersed and can be transformed into a broader spectrum of connected lines. Because of the occurrence of diffraction, the light with a particular wavelength can be conserved whereas because of the interference, other light waves with different wavelengths can be differentiated. The concept of diffraction can also be applied in our practical lives. 


We often see a particular form of rainbow pattern taking place on the surface of the CD or DVD and it is one of the practical examples of diffraction. These are some foundational concepts of physics and optical science that explains the characteristics of lights, the importance of different wavelengths, and the tasks carried out by different kinds of medium and how it can influence the wavelength of the lights. 


Understanding this concept is particularly helpful for those students who want to pursue their future studies in the field of physics and optical science. Moreover, the aspirant students who want to qualify for engineering entrance examinations or any other entrance examinations like JEE Main or Advanced should have a clear understanding of the topic since there will be questions from each of the chapters that are included in their syllabus. To get a better learning experience, download the free course materials from the website of Vedantu and also you can join the free classes to have a detailed overview regarding the various subjects like physics, chemistry, mathematics etc.


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