Shift in Interference Pattern

Matter is the basis of everything in the universe. From observable matter to the dark matter, it is the very foundation of why the universe exists. Therefore, the study of matter and its form is very important. One notable theory is about the concept of the matter wave, and how a stream of particles when small enough can be constituted as a wave.

This disturbance that is created by a particle, when it moves through a medium in space, is called a wave. For a particle like an electron, the wave function is a special quantity that gives the probability of a particle being in a specific place, provided that the particle behaves like a matter wave.

Interference of a Wave

Now that we know particles can also travel as waves, the next important concept to understand is the interaction between them. When two forces are applied on a body, they undergo vector addition to yield the total force on the body. When two bodies collide with each other, they undergo elastic or inelastic collision. But what happens when two waves meet each other when travelling in a medium?

Waves are made up of crests and troughs. When two waves meet, their crests and troughs clash with each other to yield a completely new set of crests and troughs. This phenomenon is called the interference of waves. In other words, the disturbance that is caused in a medium due to two waves interacting with each other is a net total of the effect that the two waves have on the medium.

Different types of Interference

Destructive interference

• Destructive interference occurs at instances where waves conjoin in such a way that they totally neutralise each other. 
• At the instance of the waves when they destructively interfere, they should possess the identical magnitude in the inverted directions.
• There have been several compulsive wave phenomena that have occurred naturally, which cannot be described by a single wave.
•  For understanding the destructive phenomena, we should inspect them on the basis of combining the waves. For inspecting these, we use the principle of superposition that states:
• “If two or more waves are travelling in a medium, the resulting wave function is the algebraic total of the individual wave function.”

Constructive Interference

• At the time of two waves that traverse in an identical direction and find themselves in each one’s phase, the magnitude they both possess gets summed up for a new wave to be formed. 
• This phenomenon which occurs on these waves is called constructive interference.
• The ascending movement occurs during the time the waves are affected by constructive interference. 
• Thus, the upward displacement of the medium is greater than the displacement of the two interfering pulses.
• The time that two waves of identical frequency meet each other at a certain point, then the final magnitude is the addition of the independent magnitudes of each wave. 
• There can also be observations made as per the final wave to have amplitude at higher frequency compared to that of each individual wave that is affected by the interference.  
• Constructive interference occurs when the phase difference between the waves is an even multiple of π (180°).

Young’s Double Slit experiment

• Young’s Double slit experiment is a famous experiment where a light source is made to be incident on two slits in a thin sheet of paper or some other diffractive material. 
• When light passes through these slits, it undergoes diffraction.
• This diffraction of light causes the light to get split into multiple semi diffracted light waves. These light waves interfere with each other to create a pattern called the interference pattern. 
• As the distance of the light from the slits and the separation between the slits is changed, it causes a shift of the interference pattern.
• The contrast in the fringes in an interference pattern depends on the intensity of the source light. 
• The contrast in the fringes is good when the ratio of intensities of the two semi diffracted waves is equal to one.
• The young’s double slit experiment is a popular example of a shift of the interference pattern. 
• As the material of the slit keeps changing, the fringe pattern also keeps changing, this gives us an idea of how the interference of waves shifts too. 

Reasons for Shift in Interference Pattern

• The interference pattern that we observe between two waves relies on two important factors. 
• A change in these factors results in a shift in the interference pattern. The first factor is the wavelength of the two waves. 
• We know that interference is the direct interaction between the crests and troughs of the two waves, and wavelength is the distance between two consecutive crests or troughs.
• Therefore, when there is a change in the wavelength of the waves, the interference pattern of the waves also changes. 
• The second reason can be the distance between the sources of the two waves. When the two sources of the waves are separated, there is again a change in the interaction of their wavelengths and hence the interference pattern also changes.

Conclusion

Waves are made up of crests and troughs. When two waves meet, their crests and troughs clash with each other to yield a completely new set of crests and troughs. This phenomenon is called the interference of waves. In other words, the disturbance that is caused in a medium due to two waves interacting with each other is a net total of the effect that the two waves have on the medium.

The interference of waves can be observed when they are in the visible spectrum, and the pattern that is formed is called the interference pattern. Waves can interact such that they cause two types of interference, constructive and destructive interference.

Constructive interference occurs when the net interference becomes a sum of the individual interferences caused by the wave, whereas destructive interference is caused when the individual disturbances of two waves cancel each other out.