Wave Interference ( Read ) | Physics | CK Foundation
When two or more waves meet, they interact with each other. The interaction of waves with other waves is called wave interference. Wave. When sound waves meet other sound waves they combine. Combining waves with the same frequency (speed), loudness and polarity will lead to a new up when in phase” sounds like the waves fade in and out, and is called “BEATING”. Interference is what happens when two or more waves come together. Although the waves interfere with each other when they meet, they continue traveling as If the end is fixed, the pulse will be reflected upside down (also known as a ° phase shift). combining these gives L / v = 1 / 2f, so f = v / 2L.
What effect will the meeting of the waves have upon the appearance of the medium? Will the two waves bounce off each other upon meeting much like two billiard balls would or will the two waves pass through each other? These questions involving the meeting of two or more waves along the same medium pertain to the topic of wave interference.
Wave interference is the phenomenon that occurs when two waves meet while traveling along the same medium. The interference of waves causes the medium to take on a shape that results from the net effect of the two individual waves upon the particles of the medium.
To begin our exploration of wave interference, consider two pulses of the same amplitude traveling in different directions along the same medium. Let's suppose that each displaced upward 1 unit at its crest and has the shape of a sine wave. As the sine pulses move towards each other, there will eventually be a moment in time when they are completely overlapped. At that moment, the resulting shape of the medium would be an upward displaced sine pulse with an amplitude of 2 units.
The diagrams below depict the before and during interference snapshots of the medium for two such pulses. The individual sine pulses are drawn in red and blue and the resulting displacement of the medium is drawn in green. Constructive Interference This type of interference is sometimes called constructive interference. Constructive interference is a type of interference that occurs at any location along the medium where the two interfering waves have a displacement in the same direction.
In this case, both waves have an upward displacement; consequently, the medium has an upward displacement that is greater than the displacement of the two interfering pulses. Constructive interference is observed at any location where the two interfering waves are displaced upward. Constructive interference, then, can produce a significant increase in amplitude. The following diagram shows two pulses coming together, interfering constructively, and then continuing to travel as if they'd never encountered each other.
Another way to think of constructive interference is in terms of peaks and troughs; when waves are interfering constructively, all the peaks line up with the peaks and the troughs line up with the troughs. Destructive interference Destructive interference occurs when waves come together in such a way that they completely cancel each other out.
When two waves interfere destructively, they must have the same amplitude in opposite directions. When there are more than two waves interfering the situation is a little more complicated; the net result, though, is that they all combine in some way to produce zero amplitude.
In general, whenever a number of waves come together the interference will not be completely constructive or completely destructive, but somewhere in between. It usually requires just the right conditions to get interference that is completely constructive or completely destructive. The following diagram shows two pulses interfering destructively. Again, they move away from the point where they combine as if they never met each other. Reflection of waves This applies to both pulses and periodic waves, although it's easier to see for pulses.
Interference of Waves
Consider what happens when a pulse reaches the end of its rope, so to speak. The wave will be reflected back along the rope. If the end is free, the pulse comes back the same way it went out so no phase change. If the pulse is traveling along one rope tied to another rope, of different density, some of the energy is transmitted into the second rope and some comes back.
For a pulse going from a light rope to a heavy rope, the reflection occurs as if the end is fixed. A white light fringe pattern can be considered to be made up of a 'spectrum' of fringe patterns each of slightly different spacing.
If all the fringe patterns are in phase in the centre, then the fringes will increase in size as the wavelength decreases and the summed intensity will show three to four fringes of varying colour. Young describes this very elegantly in his discussion of two slit interference.
Since white light fringes are obtained only when the two waves have travelled equal distances from the light source, they can be very useful in interferometry, as they allow the zero path difference fringe to be identified. Traditionally, interferometers have been classified as either amplitude-division or wavefront-division systems.
- Interference of Waves
In an amplitude-division system, a beam splitter is used to divide the light into two beams travelling in different directions, which are then superimposed to produce the interference pattern. The Michelson interferometer and the Mach-Zehnder interferometer are examples of amplitude-division systems.
In wavefront-division systems, the wave is divided in space—examples are Young's double slit interferometer and Lloyd's mirror. Interference can also be seen in everyday phenomena such as iridescence and structural coloration.