Difference Between Diffraction and Interference

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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, do 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 cancelled.

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Difference Between Interference and Diffraction Class 12


Interference

Interference is the phenomenon that takes place when the meeting of the two waves takes 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 travelling 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.


State Two Important Difference Between Interference and Diffraction

Interference 

Diffraction

In interference, it happens in a way that the superposition of waves starts from varying wavefronts. It means there is a phase difference between the two waves or they are not coherent waves. 

In diffraction, it happens in a way that the superposition starts from different portions of the same wavefronts.


It means there is zero phase difference between the waves that come from the sources or they are the coherent sources. 

All bright fringes in an interference pattern are of the same intensity. 

The intensity of bright fringes in a diffraction pattern decreases when they are taken away from the bright side; however, they can be brightened by bringing these near to the central bright fringe.  

FAQ (Frequently Asked Questions)

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

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


A light undergoes 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.

Question 2: Describe the Two Categories of Interference.

Answer: 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.

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

Answer: 


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.