# Two mechanical waves meet and coincide

### Interference | tankekraft.info

Mechanical waves, such as sound, require a medium through which to travel, while In interference, when two waves meet, they can interfere constructively, then the crests of one wave will coincide with the troughs of the other and the. a. mechanical kinetic The material through which a mechanical wave travels is a. a medium. b. empty .. When two waves having displacements in opposite directions meet, exactly coincide, the resulting displacement of the medium. ____ 9. Two mechanical waves meet and coincide. One wave has a positive displacement from the equilibrium position, and the other wave has a negative.

Waves can be seen as a means of transferring energy from one place to another. A disturbance in a medium caused by a series of identical wave pulses is known as a periodic wave.

## A longitudinal wave is:

A transverse wave is a wave where the direction of the vibration is perpendicular to the direction in which the wave travels. The top of the wave is called a crest, the bottom of the wave is called a trough. The maximum distance of any particle of the medium from the undisturbed position is called the amplitude A. The disturbance produced by one complete vibration of the source is called an oscillation or cycle i.

Frequency is measured in units called hertz Hz. The parallel lines are drawn to represent the position of an advancing wave. The lines are formed by joining points that are in phase, such as the crests. When discussing the various properties of waves, we will use the idea of wave fronts.

When a wave front strikes an obstacle, it is reflected. The angle of incidence equals the angle of reflection. When waves travel from one medium to another, they change speed. Refraction is the change in direction of a wave as it passes from one medium to another. As the sound wave passes through the opening of the door, it is diffracted and spreads out in all directions behind the door. When a wave front strikes an obstacle or a gap, it tends to spread out in the region behind the obstacle or gap.

The greater the wavelength of the wave compared to the width of the obstacle, the greater the extent to which the wave spreads out. For a wave of a given wavelength, the narrower the gap through which the wave passes, the greater the diffraction will be. Polarisation occurs when the plane of vibration of a wave is restricted to one plane only.

## Interference of Waves

Only transverse waves can be polarised. Vertically Horizontally polarised polarised. A source of white light will consist of a number of waves vibrating in all directions. Polaroid sunglasses work by coating the lenses of the glasses with a material which will only allow light of one plane of vibration to pass through.

All other waves are absorbed. Light which has been polarised in such a way is said to be plane polarised. What happens when two or more waves meet at a point? The resultant displacement at that point is equal to the algebraic sum of the individual displacements at that point. Principle of superposition If waves from coherent sources meet and interfere with each other an interference pattern is produced.

### Interference of Waves

Coherent sources are sources which have the same frequency and are in phase with each other. The amplitude of the resulting wave is equal to the algebraic sum of the amplitudes of the interfering waves. Depending on the point at which waves meet and interfere, the resultant amplitude will either be greater or less than the initial amplitudes.

Constructive interference occurs when two waves meet and the amplitude of the resulting wave is greater than the amplitudes of the individual waves. Destructive interference occurs when two waves meet and the amplitude of the resulting wave is less than the amplitudes of the individual waves.

If two or more coherent waves meet and interfere, then an interference pattern is produced. Diagram shows the interference pattern produced in a ripple tank, by two coherent point sources. The Doppler Effect is the apparent change in frequency due to the relative motion between source and observer. For sound waves the Doppler effect produces a change in pitch. For light waves a change in colour is produced. The wave is emitted in all directions from a point source, with equally spaced wave fronts movie A moving source S emits a wave of given wavelength and frequency.

The frequency appears to be decreasing. For waves of the same amplitude interfering constructively, the resulting amplitude is times larger than the amplitude of an individual wave.

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.

### wave | Behavior, Definition, & Types | tankekraft.info

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

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.

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. But it is also observed when both interfering waves are displaced downward. This is shown in the diagram below for two downward displaced pulses.

In this case, a sine pulse with a maximum displacement of -1 unit negative means a downward displacement interferes with a sine pulse with a maximum displacement of -1 unit. These two pulses are drawn in red and blue. The resulting shape of the medium is a sine pulse with a maximum displacement of -2 units. Destructive Interference Destructive interference is a type of interference that occurs at any location along the medium where the two interfering waves have a displacement in the opposite direction.

This is depicted in the diagram below. In the diagram above, the interfering pulses have the same maximum displacement but in opposite directions. The result is that the two pulses completely destroy each other when they are completely overlapped.