# 3 Types Of Interference Of Light:Detailed Facts

In this topic, we are going to discuss different types of interference of light that is observed in nature and will exhaustively talk about each type of interference with detailed facts.

Based on how the light rays interfere with each, we can classify the interference of light as follows:-

## Constructive Interference

When two different waves interfere in such a way that, the crest of one way is superimposed on the crest of another wave then it is called constructive interference.

The below figure shows, how two waves superimpose to form a constructive interference pattern

The brightest fringes are formed due to constructive interference. The resultant wave derives the amplitude which is the resultant amplitudes of the two superimposed waves. Since both the crests of the wave overlap with each other, the resultant amplitude is greater than both the waves.

The crest of one wave falls exactly on the crest of another wave thus giving the phase difference zero, and hence are said to be in phase. Also, the displacement of the waves in a fixed time period is equal. Therefore the bright fringes are obtained on the screen due to crest to crest overlapping of the waves.

Read more on 5+ Constructive Interference Examples: Detailed Facts.

## Destructive Interference

If the crest of one wave is imposed on the trough of another wave when two waves are superimposed on each other, then the interference of the two waves is called destructive interference.

The below figure clarifies how two waves superimpose to form a constructive interference pattern

The crest of wave 1 overlaps with a trough of the second wave. Hence, the phase difference of both the wave is 180 degrees, and hence the waves are said to be out of phase. The displacement of the wave is not unique in a given time interval.

The waves on interfering, vanish together, giving zero amplitude and no intensity. As there is no intensity of light given, the dark fringes are produced due to destructive interference.

Read more on 3+ Destructive Interference of Light Example: Detailed Facts.

## Partial Interference

When two waves of the same wavelength and frequency are superimposed in such a way that the crest and trough of the wave don’t overlap on each other. This is the summing of both constructive and destructive interference.

The two waves imposing on each other are shown in the below diagrams.

The waves are partially imposed, hence called partially interfered. If the two sound waves show partial interference then the resultant sound wave produced will be heard partially muted frequently.

Partial interference is of two types, partial constructive interference, and partial destructive interference. The partial constructive interference is when the crest of two waves are not exactly superimposed on each other or the phase of each wave is not the same. And if the crest of one wave does not exactly superimpose on the trough of the second wave then it is called partial destructive interference.

Read more on Constructive Interference vs Destructive Interference: Detailed Facts.

## Thin-Film Interference

When a ray of light reflects from two surfaces of the very thin layer of solid or liquid, the reflected light rays from the top and the bottom surfaces interfere and give colorful patterns of light.

During this type of interference, a part of the light is reflected and a part of the light is transmitted. Examples of thin-film interferences are light reflected from soap bubbles, the reflection of light from the pool, a thin film of oil on water, a thin layer of liquid on road, etc.

## What is interference?

Two or more beams of light trespassing each other is called interference of light.

Two waves superimpose to produce a resulting wave having the same amplitude or either increase or decrease the amplitude of the emerging wave.

The interference of light gives the dark fringes which are called minima where the intensity of the light is zero and the bright fringes called the maxima where the intensity of the light rays is maximum.

Read more on 7+ Interference Of Light Examples: Detailed Facts.

## How interference is different from Diffraction?

Interference is the overlapping of two or more waves whereas diffraction is the bending of light waves.

The fringes formed due to interference of light are equally spaced and not like the one observed in the diffraction pattern of light where the spacing between the fringes goes on decreasing from the center.

The intensity of the light is highest at the center if we see the diffraction pattern, but in the case of the interference pattern, the intensity of all the maxima has the same intensity. Dislike the diffraction, the fringes are equally spaces in the interference pattern. The minima observed in the diffraction of light are not perfectly dark whereas the dark fringes seen in the interference pattern are perfectly dark.

## What is Quantum Interference?

From the word quantum, it is understood that it resembles the quanta of particles.

The addition of a wave function of a particle based on the probability of finding the particle at two different positions in a wave interfering among itself is called quantum interference.

It can be denoted by the equation below,

$\psi (x,t)=\psi _A(x,t)+\psi _B(x,t)$

Where $\psi (x,t)$ is a linear superposition of two waves

$\psi _A(x,t)$ is a wave function of a particle in condition A

$\psi _B(x,t)$ is a wave function of a particle in condition B

The probability of finding the particle at certain position ‘x’ is the square of the wave function of the particle.

Hence,

$P=\left ( \psi (x,t) \right )^2=\left ( \psi _A(x,t)+\psi _B(x,t) \right )^2$

$P=\psi _A^2(x,t)+\psi _B^2(x,t)+\psi _A^*(x,t)\psi _B(x,t)+\psi _A(x,t)\psi _B^*(x,t)$

The terms $\psi _A^*(x,t)\psi _B(x,t)$ and $\psi _A(x,t)\psi _B^*(x,t)$ represent the quantum interference. Whereas, the term $\psi _A^2(x,t)$ gives the exact probability of a particle in condition A and the term $\psi _B^2(x,t)$ gives the exact probability of a particle in condition B.

## What is Resonance?

Resonance occurs when the frequency matches the natural frequency of the object.

The repetitive constructive interference results in resonance as the frequency of the wave matches the natural frequency of vibration of any object.

If you hammer a tuning fork and held it near the hollow vessel, the vibrations produced due to the tuning fork will travel across the vessel; and once the frequency of the vibrating waves matches the natural frequency of the hollow vessel, a resonating sound will be produced through a vessel.

Read more on 5+ Interference Of Sound Examples: Detailed Facts.

## What are Beats?

It is an interference of two sound waves of similar frequencies and a constant phase difference.

The addition of two waves having similar frequencies will overlap in a way making nodes and antinodes; the distance between two antinodes is called the beat.

The superimposition of the wave and the resultant wave produced will look like as shown below

This is used to tune any musical instrument. Suppose you want to tune string 1 on guitar, so lift a tuning fork ringing “E” note and ring a note while you plug your string 1 which is slightly out of tune, then both the notes will appear to be in synchronization initially and then will go out of tune.

## What is phase of a wave?

A phase of a wave is calculated on the axis of propagation of a wave.

A complete wavelength ‘$\lambda$’ of one wave, that is the addition of sine and cosine function, gives a complete phase of 360 degrees. Half of the wavelength will give 180 degrees.

## What is a phase difference between the two waves?

The phase difference is the degree to which one wave is lagging behind the phase of the other wave.

If the two waves overlap exactly on crest-to-crest of each other then the phase difference is zero. For partial constructive or partial destructive interference, the phase difference is greater than 0 and less than 90 degrees.

AKSHITA MAPARI

Hi, I’m Akshita Mapari. I have done M.Sc. in Physics. I have worked on projects like Numerical modeling of winds and waves during cyclone, Physics of toys and mechanized thrill machines in amusement park based on Classical Mechanics. I have pursued a course on Arduino and have accomplished some mini projects on Arduino UNO. I always like to explore new zones in the field of science. I personally believe that learning is more enthusiastic when learnt with creativity. Apart from this, I like to read, travel, strumming on guitar, identifying rocks and strata, photography and playing chess. Connect me on LinkedIn - linkedin.com/in/akshita-mapari-b38a68122