Visit this website to view an excellent simulation of a ripple tank for demonstrating wave-related phenomena. Add to collection. Related content This article is part of an article series : Sound — understanding standing waves Sound — visualising sound waves Sound — resonance Sound — beats, the Doppler effect and sonic booms with accompanying investigations: Measuring the speed of sound Investigating sound wave resonance Visit the sound topic for additional resources.
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Ultrasound is sound with a frequency higher than 20 kHz. This is above the human range of hearing. The most common use of ultrasound, creating images, has industrial and medical applications. The use of ultrasound to create images is based on the reflection and transmission of a wave at a boundary.
When an ultrasound wave travels inside an object that is made up of different materials such as the human body , each time it encounters a boundary e. The reflected rays are detected and used to construct an image of the object.
A sound wave is transmitted and bounces off the seabed. Because the speed of sound is known and the time lapse between sending and receiving the sound can be measured, the distance from the ship to the bottom of the ocean can be determined. Sonar : Ships on the ocean make use of the reflecting properties of sound waves to determine the depth of the ocean.
Just as ships on the ocean, certain animals, like dolphins and bats, make use of sounds waves sonar to navigate or find their way. Ultrasound waves are sent out then reflected off the objects around the animal. Privacy Policy. Skip to main content. Search for:. Interactions with Sound Waves. Superposition Superposition occurs when two waves occupy the same point the wave at this point is found by adding the two amplitudes of the waves.
Learning Objectives Identify conditions required for the superposition of two waves. Key Takeaways Key Points When two waves occupy the same point, superposition occurs. Superposition results in adding the two waves together. Constructive interference is when two waves superimpose and the resulting wave has a higher amplitude than the previous waves.
Destructive interference is when two waves superimpose and cancel each other out, leading to a lower amplitude. Most wave superpositions involve a mixture of constructive and destructive interference since the waves are not perfectly identical.
Key Terms superimpose : To place an object over another object. Interference Interference occurs when multiple waves interact with each other, and is a change in amplitude caused by several waves meeting. Learning Objectives Contrast constructive and destructive interference. Key Takeaways Key Points 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, constructive and destructive. In constructive interference, the amplitudes of the two waves add together resulting in a higher wave at the point they meet.
In destructive interference, the two waves cancel out resulting in a lower amplitude at the point they meet. Key Terms displacement : A vector quantity that denotes distance with a directional component. Beats The superposition of two waves of similar but not identical frequencies produces a pulsing known as a beat.
With this, our condition for constructive interference can be written:. Here, the variable n is used to specify an integer and can take on any value, as long as it is an integer. This ensures that we only add whole numbers of wavelengths. Once we have the condition for constructive interference, destructive interference is a straightforward extension.
The basic requirement for destructive interference is that the two waves are shifted by half a wavelength. But, since we can always shift a wave by one full wavelength, the full condition for destructive interference becomes:.
Now that we have mathematical statements for the requirements for constructive and destructive interference, we can apply them to a new situation and see what happens.
To create two waves traveling in opposite directions, we can take our two speakers and point them at each other, as shown in the figure above. We again want to find the conditions for constructive and destructive interference. As we have seen, the simplest way to get constructive interference is for the distance from the observer to each source to be equal. Looking at the figure above, we see that the point where the two paths are equal is exactly midway between the two speakers the point M in the figure.
At this point, there will be constructive interference, and the sound will be strong. It makes sense to use the midpoint as a reference, as we know that we have constructive interference. How far must we move our observer to get to destructive interference? If we move to the left by an amount x, the distance R 1 increases by x and the distance R 2 decreases by x.
If R 1 increases and R 2 decreases, the difference between the two R 1 — R 2 increases by an amount 2x. Now comes the tricky part. To put it another way, in the situation above, if you move one quarter of a wavelength away from the midpoint, you will find destructive interference and the sound will sound very weak, or you might not hear anything at all. What happens if we keep moving our observation point? In other words, if we move by half a wavelength, we will again have constructive interference and the sound will be loud.
As we keep moving the observation point, we will find that we keep going through points of constructive and destructive interference.
This is a bit more complicated than the first example, where we had either constructive or destructive interference regardless of where we listened.
In this case, whether there is constructive or destructive interference depends on where we are listening. However, the fundamental conditions on the path difference are still the same. What does this pattern of constructive and destructive interference look like? Where have we seen this pattern before? At a point of constructive interference, the amplitude of the wave is large and this is just like an antinode.
At a point of destructive interference, the amplitude is zero and this is like an node. Destructive interference leads to only a momentary condition in which the medium's displacement is less than the displacement of the largest-amplitude wave. The two interfering waves do not need to have equal amplitudes in opposite directions for destructive interference to occur. The resulting displacement of the medium during complete overlap is -1 unit. This is still destructive interference since the two interfering pulses have opposite displacements.
In this case, the destructive nature of the interference does not lead to complete cancellation. Interestingly, the meeting of two waves along a medium does not alter the individual waves or even deviate them from their path. This only becomes an astounding behavior when it is compared to what happens when two billiard balls meet or two football players meet. Billiard balls might crash and bounce off each other and football players might crash and come to a stop. Yet two waves will meet, produce a net resulting shape of the medium, and then continue on doing what they were doing before the interference.
The task of determining the shape of the resultant demands that the principle of superposition is applied. The principle of superposition is sometimes stated as follows:. When two waves interfere, the resulting displacement of the medium at any location is the algebraic sum of the displacements of the individual waves at that same location.
In the cases above, the summing the individual displacements for locations of complete overlap was made out to be an easy task - as easy as simple arithmetic:. In actuality, the task of determining the complete shape of the entire medium during interference demands that the principle of superposition be applied for every point or nearly every point along the medium.
As an example of the complexity of this task, consider the two interfering waves at the right. A snapshot of the shape of each individual wave at a particular instant in time is shown. To determine the precise shape of the medium at this given instant in time, the principle of superposition must be applied to several locations along the medium.
A short cut involves measuring the displacement from equilibrium at a few strategic locations.
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