# When two waves meet they interact

### When two waves meet they interact what is this interaction called

What is the interaction between two waves that meet? Interference. This can result in either constructive interference, resulting in increased amplitude. Interference is a phenomenon of wave interactions. When two waves meet at a point, they interfere with each other. There are two types of interference. The bending of the waves as they enter a different medium is called. refraction. All waves When two waves meet, they interact. This interaction is called?.

The light waves will be traveling the same distance, so they will be traveling the same number of wavelengths. That means that there will always be constructive interference at that spot, so we will always see a bright spot on the wall in the middle. At that point, one of the waves will hit the wall with a crest when the other hits with a trough, so they will effectively cancel one another out, resulting in a dark spot there.

This will result in another bright spot on the wall.

- Interference of Waves
- Wave interference

This pattern will keep alternating so that we get a pattern of light spots and dark spots, both above and below our center bright spot. Figure of diffraction pattern on the opposite wall If your slits are further apart, the light waves will be coming from spots that are further apart. That means that their path lengths will be more different from one another, giving bright spots that are closer together.

We can pretend to divide our slit into pieces, and compare the path lengths of the light coming from these pieces to one another to discover what sort of interference pattern we will get when they interact.

They are an equal distance from the center of the slit, so their path lengths to the center point on the wall will be the same.

## Diffraction and constructive and destructive interference

We know that that means they will interfere constructively with one another. If we choose two points that are further in, but still the same distance from the middle of the slit, they will also have equal path lengths to the center point on the wall. They will also interfere constructively with one another. So, we can see that there is a lot of constructive interference going on at that center point, in fact, there will be a major bright spot there because of it.

If we want to find a spot on the wall that is dark, we have to find where there is the most destructive interference. Figure of waves passing though single slit toward two different targets on opposite wall Because all of these pairs are the same distance apart across the slit, if we measure the path length from each pair to the same spot on the wall, each pair will have the same difference in path length.

### Wave interference - Wikipedia

Figure of single-slit diffraction pattern If we compare single-slit diffraction to the double-slit interference pattern, the spots are much larger and more spread out. In particular, the center bright spot is much larger than it would be for double slits with the same width. We can view diffraction as light spreading out when it comes up to a hole or other barrier, and trying to get around that barrier. In the process of spreading out, it interferes with itself to create the pattern of light and dark spots that we call a diffraction pattern.

Double slit interference with diffraction When we talked about double slit interference, we pretended that only one light wave could go through each slit at a time. If instead we realize that there are a few light waves travelling through each of the two slits at once, then we can see that there will be a diffraction pattern for each individual slit in addition to the two-slit interference pattern.

This pattern will hold our double-slit interference pattern back, limiting how bright the bright spots can be at any given point on the wall. If we have a bright spot in the diffraction pattern, then our interference bright spots can be as bright at we want.

But, if we have a diffraction dark spot, then the bright spots in our interference pattern cannot be any brighter than the diffraction dark spot, and will disappear altogether. Figure of single slit envelope, double slit diffraction and resulting single slit diffraction and double slit diffraction The interference pattern will come from the light from the two slits interacting, and the diffraction pattern will come from the light from each individual slit interacting with itself.

Consider the following Imagine our scenario of interference from walkie talkie signals. Say the receiver is between the person sending the walkie talkie signal and a solid rock cliff, and we know that the wavelength of the walkie talkie signal is 1 meter.

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. Consider what happens when a pulse reaches the end of its rope, so to speak.

The wave will be reflected back along the rope.

### Interference of Waves

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. From heavy to light, the reflection is as if the end is free. Standing waves Moving on towards musical instruments, consider a wave travelling along a string that is fixed at one end. The reflected wave will interfere with the part of the wave still moving towards the fixed end. Typically, the interference will be neither completely constructive nor completely destructive, and nothing much useful occurs.

In special cases, however, when the wavelength is matched to the length of the string, the result can be very useful indeed. Consider one of these special cases, when the length of the string is equal to half the wavelength of the wave.

The second harmonic will be twice this frequency, the third three times the frequency, etc. The different harmonics are those that will occur, with various amplitudes, in stringed instruments. String instruments and transverse standing waves In general, the special cases the frequencies at which standing waves occur are given by: