Interference

In physics, interference is a phenomenon where two waves interfere to form a resulting wave of greater, lesser, or equal amplitude. Constructive and destructive interference arise from the interaction of waves that are correlated or coherent, either because they originate from the same source or because they have the same or nearly the same frequency. Interference effects can be observed in all types of waves, such as light waves, radio waves, surface water waves, gravity waves or matter waves.

Interference Definition

Interference in physics is the net effect of the combination of two or more wave trains traveling on paths that intersect or coincide. The effect is that of the sum of the amplitudes of the individual waves at any point affected by more than one wave. If two of the components have the same frequency and phase (i.e. they vibrate at the same speed and at the same time), the wave amplitudes reinforce each other and create constructive interference. But if the two waves are 1/2 i.e. half period out of phase (i.e. one is minimum while the other is maximum), the result is destructive interference, producing complete cancellation if they are of equal amplitude.

Constructive Interference

When two waves come together, their effects add up. If the crests or the highest parts of the waves are perfectly aligned, then the crest of the total wave is the sum of the heights of the two original crests. Similarly, if the lowest parts of the waves (the troughs) are correctly aligned, the combined trough will be equal to the depth of the two original troughs combined. This is known as constructive interference, where two waves (of the same wavelength) interact in such a way that they align, creating a new wave that is larger than the original wave.

Destructive Interference

Destructive interference is a type of interference that occurs anywhere along the medium where the two interfering waves travel in the opposite direction. For example, when a sine pulse with a maximum displacement of +1 unit encounters a sine pulse with a maximum displacement of -1 unit, destructive interference occurs.

Principal of Superposition

Let us take the example of a wave chain to define the wave superposition principle which is based on the superposition theorem. And according to this, the net displacement of any component on the string for a given time is equal to the algebraic totality of the displacements caused by each wave. Therefore, this method of summing the individual waveforms for the evaluation of the net waveform is called the principle of superposition. The principle of superposition is expressed by stating that superimposed waves add algebraically to create a resultant wave. According to the principle, the superimposed waves (at the frequencies f₁, f₂, f₃….,fₙ) do not interfere with the movement or displacement of each other.

Interference Fringes

When laser light is diffracted through the two barrier slits, each diffracted wave encounters the other in a series of steps. Sometimes the waves meet in one stage (or in phase; constructive interference), sometimes they meet out of phase (or out of phase; destructive interference), and sometimes they meet partially in phase. When the waves meet in phase, they get added together due to constructive interference and a bright area appears on the screen. In areas where the waves meet completely out of phase, they will get subtracted from each other causing destructive interference and a dark area will appear in that part of the screen. The resulting patterns on the screen, a product of the interference between the two beams of diffracted laser light, are often called interference fringes.

Real Life example of Interference

Other applications of light interference are long-distance measurements with lasers. In this case, lasers can be used to measure very small distances over a range of many KMs. This is achieved by splitting the laser beam and bouncing it off different surfaces. Analysis of the resulting interference fringes (by recombining the separated laser beams) will produce a remarkably accurate estimate of the distance between the two objects. Holograms also rely on light interference to create their three-dimensional images. With reflection holograms, both a reference and an object light beam are reflected from opposite sides onto a thick foil. These rays interfere to create light and dark areas that correspond to a three-dimensional appearing image. Transmission holograms use reference and object light rays on the same side of the film to create a similar effect. Interference also occurs with sound waves and waves induced in floating pool water. A very concise and simple interference experiment can be done at home with a sink full of water and two marbles. First, allow the water to become still, and then simultaneously drop the marbles into the water from a height of about a foot (about 10-14 inches apart). As with light waves, the two marbles create a series of waves in the existing water in all directions. The waves formed in the area between where the marbles enter the water will eventually collide. If they collide simultaneously, they add up constructively into a larger wave, and if they collide out of step, they cancel out destructively. You can try this on your own.

Conclusion

Hopefully this interference article is useful for you, the article includes interference and its types and you will get an idea through it what interference actually is. Moreover in this article we have discussed the superposition principle and interference fringes too which will give you some idea about the interference in detail. And lastly, the article also includes real life examples related to interference which will make you understand interference in detail.