As physical objects have wave-like properties at the atomic level , diffraction also occurs with matter and can be studied according to the principles of quantum mechanics. Italian scientist Francesco Maria Grimaldi coined the word diffraction and was the first to record accurate observations of the phenomenon in The effects of diffraction are often seen in everyday life.
The most striking examples of diffraction are those involving light; for example, the closely spaced tracks on a CD or DVD act as a diffraction grating to form the familiar rainbow pattern seen when looking at a disk. This principle can be extended to engineer a grating with a structure such that it will produce any diffraction pattern desired; the hologram on a credit card is an example.
Diffraction in the atmosphere by small particles can cause a bright ring to be visible around a bright light source like the sun or the moon. A shadow of a solid object, using light from a compact source, shows small fringes near its edges.
All these effects occur because light propagates as a wave. It is just a question of usage, and there is no specific, important physical difference between them. While diffraction occurs whenever propagating waves encounter such changes, its effects are generally most pronounced for waves where the wavelength is roughly similar to the dimensions of the diffracting objects. 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. Thus, approximately 20 locations have been picked and labeled as A, B, C, D, etc.
The actual displacement of each individual wave can be counted by measuring from the equilibrium position up to the particular wave. At position A, there is no displacement for either individual wave; thus, the resulting displacement of the medium at position will be 0 units. At position B, the smaller wave has a displacement of approximately 1.
Thus, the resulting displacement of the medium will be approximately 3. At position C, the smaller wave has a displacement of approximately 2 units; the larger wave has a displacement of approximately 4 units; thus, the resulting displacement of the medium will be approximately 6 units. At position D, the smaller wave has a displacement of approximately 1. This process can be repeated for every position.
When finished, a dot done in green below can be marked on the graph to note the displacement of the medium at each given location. The actual shape of the medium can then be sketched by estimating the position between the various marked points and sketching the wave. This is shown as the green line in the diagram below. Physics My highlights. Table of contents. Chapter Review. Test Prep. By the end of this section, you will be able to do the following: Describe superposition of waves Describe interference of waves and distinguish between constructive and destructive interference of waves Describe the characteristics of standing waves Distinguish reflection from refraction of waves.
Teacher Support The learning objectives in this section will help your students master the following standards: 7 Science concepts. The student knows the characteristics and behavior of waves. The student is expected to: D investigate the behaviors of waves, including reflection, refraction, diffraction, interference, resonance, and the Doppler effect.
In addition, the High School Physics Laboratory Manual addresses content in this section in the lab titled: Waves, as well as the following standards: 7 Science concepts. The student is expected to: D investigate behaviors of waves, including reflection, refraction, diffraction, interference, resonance, and the Doppler effect. Waterborough, Wikimedia Commons. Teacher Support The horizontal waves in the picture bounce off the wall of the lake seen in the front part of the picture.
Wave Interference Click to view content. Make waves with a dripping faucet, audio speaker, or laser! Add a second source or a pair of slits to create an interference pattern. Click to view content. In the water tab, compare the waves generated by one drip versus two drips. What happens to the amplitude of the waves when there are two drips? Is this constructive or destructive interference? Why would this be the case? The oscillations are at fixed locations in space and result from alternating constructive and destructive interferences.
What is the superposition of waves? When a single wave splits into two different waves at a point When two waves combine at the same place at the same time. How do waves superimpose on one another?
By adding their frequencies By adding their wavelengths By adding their disturbances By adding their speeds. What is interference of waves? Beats are produced by the superposition of two waves of slightly different frequencies but identical amplitudes. The waves alternate in time between constructive interference and destructive interference, giving the resulting wave a time-varying amplitude.
The wave resulting from the superposition of two similar-frequency waves has a frequency that is the average of the two. This wave fluctuates in amplitude, or beats , with a frequency called the beat frequency.
We can determine the beat frequency by adding two waves together mathematically. These results mean that the resultant wave has twice the amplitude and the average frequency of the two superimposed waves, but it also fluctuates in overall amplitude at the beat frequency f B. The first cosine term in the expression effectively causes the amplitude to go up and down. The second cosine term is the wave with frequency f ave. This result is valid for all types of waves.
However, if it is a sound wave, providing the two frequencies are similar, then what we hear is an average frequency that gets louder and softer or warbles at the beat frequency. Piano tuners use beats routinely in their work. When comparing a note with a tuning fork, they listen for beats and adjust the string until the beats go away to zero frequency.
For example, if the tuning fork has a Hz frequency and two beats per second are heard, then the other frequency is either or Hz. Most keys hit multiple strings, and these strings are actually adjusted until they have nearly the same frequency and give a slow beat for richness. Twelve-string guitars and mandolins are also tuned using beats. While beats may sometimes be annoying in audible sounds, we will find that beats have many applications. Observing beats is a very useful way to compare similar frequencies.
There are applications of beats as apparently disparate as in ultrasonic imaging and radar speed traps. Imagine you are holding one end of a jump rope, and your friend holds the other.
If your friend holds her end still, you can move your end up and down, creating a transverse wave. If your friend then begins to move her end up and down, generating a wave in the opposite direction, what resultant wave forms would you expect to see in the jump rope?
The rope would alternate between having waves with amplitudes two times the original amplitude and reaching equilibrium with no amplitude at all. The wavelengths will result in both constructive and destructive interference.
Nodes are areas of wave interference where there is no motion. Antinodes are areas of wave interference where the motion is at its maximum point. You hook up a stereo system. When you test the system, you notice that in one corner of the room, the sounds seem dull. In another area, the sounds seem excessively loud. Describe how the sound moving about the room could result in these effects.
With multiple speakers putting out sounds into the room, and these sounds bouncing off walls, there is bound to be some wave interference. In the dull areas, the interference is probably mostly destructive.
In the louder areas, the interference is probably mostly constructive. Make waves with a dripping faucet, audio speaker, or laser! Add a second source or a pair of slits to create an interference pattern. Skip to main content.
0コメント