AskDefine | Define resonance

Dictionary Definition

resonance

Noun

1 an excited state of a stable particle causing a sharp maximum in the probability of absorption of electromagnetic radiation
2 a vibration of large amplitude produced by a relatively small vibration near the same frequency of vibration as the natural frequency of the resonating system
3 having the character of a loud deep sound; the quality of being resonant [syn: plangency, reverberance, ringing, sonorousness, sonority, vibrancy]
4 relation of mutual understanding or trust and agreement between people [syn: rapport]
5 the quality imparted to voiced speech sounds by the action of the resonating chambers of the throat and mouth and nasal cavities

User Contributed Dictionary

English

Etymology

From resonance (French résonance), from resonantia ‘echo’, from resonare ‘resound’.

Pronunciation

  • (UK) /ˈɹɛzənəns/

Noun

  1. The condition of being resonant.
  2. Something that evokes an association, or a strong emotion.
  3. The increase in the amplitude of an oscillation of a system under the influence of a periodic force whose frequency is close to that of the system's natural frequency.
  4. In the context of "nuclear physics": A short-lived subatomic particle that cannot be observed directly.
    • 2004: When experiments with the first ‘atom-smashers’ took place in the 1950s to 1960s, many short-lived heavier siblings of the proton and neutron, known as ‘resonances’, were discovered. — Frank Close, Particle Physics: A Very Short Introduction (Oxford 2004, p. 35)
  5. An increase in the strength or duration of a musical tone produced by sympathetic vibration.
  6. The property of a compound that can be visualized as having two structures differing only in the distribution of electrons.

Extensive Definition

This article is about resonance in physics. For other senses of this term, see resonance (disambiguation).
In physics, resonance is the tendency of a system to oscillate at maximum amplitude at certain frequencies, known as the system's resonance frequencies (or resonant frequencies). At these frequencies, even small periodic driving forces can produce large amplitude vibrations, because the system stores vibrational energy. When damping is small, the resonance frequency is approximately equal to the natural frequency of the system, which is the frequency of free vibrations. Resonant phenomena occur with all type of vibrations or waves; mechanical (acoustic), electromagnetic, and quantum wave functions. Resonant systems can be used to generate vibrations of a specific frequency, or pick out specific frequencies from a complex vibration containing many frequencies.

Examples

One familiar example is a playground swing, which acts as a pendulum. Pushing a person in a swing in time with the natural interval of the swing (its resonance frequency) will make the swing go higher and higher (maximum amplitude), while attempts to push the swing at a faster or slower tempo will result in smaller arcs. This is because the energy the swing absorbs is maximized when the pushes are at the resonance frequency, while some of this energy is canceled out by the inertial energy of the swing when they are not.
Resonance occurs widely in nature, and is exploited in many man-made devices. Many sounds we hear, such as when hard objects of metal, glass, or wood are struck, are caused by brief resonant vibrations in the object. Light and other short wavelength electromagnetic radiation is produced by resonance on an atomic scale, such as electrons in atoms. Other examples are:

Theory

For a linear oscillator with a resonance frequency Ω, the intensity of oscillations I when the system is driven with a driving frequency ω is given by:
I(\omega) \propto \frac.
The intensity is defined as the square of the amplitude of the oscillations. This is a Lorentzian function, and this response is found in many physical situations involving resonant systems. Γ is a parameter dependent on the damping of the oscillator, and is known as the linewidth of the resonance. Heavily damped oscillators tend to have broad linewidths, and respond to a wider range of driving frequencies around the resonance frequency. The linewidth is inversely proportional to the Q factor, which is a measure of the sharpness of the resonance.

Resonators

A physical system can have as many resonance frequencies as it has degrees of freedom; each degree of freedom can vibrate as a harmonic oscillator. Systems with one degree of freedom, such as a mass on a spring, pendulums, balance wheels, and LC tuned circuits have one resonance frequency. Systems with two degrees of freedom, such as coupled pendulums and resonant transformers can have two resonance frequencies. As the number of coupled harmonic oscillators grows, the time it takes to transfer energy from one to the next becomes significant. The vibrations in them begin to travel through the coupled harmonic oscillators in waves, from one oscillator to the next.
Extended objects that experience resonance due to vibrations inside them are called resonators, such as organ pipes, vibrating strings, quartz crystals, microwave cavities, and laser rods. Since these can be viewed as being made of millions of coupled moving parts (such as atoms), they can have millions of resonance frequencies. The vibrations inside them travel as waves, at an approximately constant velocity, bouncing back and forth between the sides of the resonator. If the distance between the sides is d\,, the length of a round trip is 2d\,. In order to cause resonance, the phase of a sinusoidal wave after a round trip has to be equal to the initial phase, so the waves will reinforce. So the condition for resonance in a resonator is that the round trip distance, 2d\,, be equal to an integral number of wavelengths of the wave:
2d = N\lambda,\qquad\qquad N \in \
If the velocity of a wave is v\,, the frequency is f = v / \lambda\, so the resonant frequencies are:
f = \frac\qquad\qquad N \in \
So the resonance frequencies of resonators, called normal modes, are equally spaced multiples of a lowest frequency called the fundamental frequency. The multiples are often called overtones. There may be several such series of resonant frequencies, corresponding to different modes of vibration.

Old Tacoma Narrows bridge failure

The collapse of the Old Tacoma Narrows Bridge, nicknamed Galloping Gertie, in 1940 is sometimes characterized in physics textbooks as a classical example of resonance. This description is misleading, however. The catastrophic vibrations that destroyed the bridge were not due to simple mechanical resonance, but to a more complicated oscillation between the bridge and winds passing through it, known as aeroelastic flutter. Robert H. Scanlan, father of the field of bridge aerodynamics, wrote an article about this misunderstanding.

Resonances in quantum mechanics

In quantum mechanics and quantum field theory resonances may appear in similar circumstances to classical physics. However, they can also be thought of as unstable particles, with the formula above still valid if the \Gamma is the decay rate and \Omega replaced by the particle's mass M. In that case, the formula just comes from the particle's propagator, with its mass replaced by the complex number M+i\Gamma. The formula is further related to the particle's decay rate by the optical theorem.

String resonance in music instruments

String resonance occurs on string instruments. Strings or parts of strings may resonate at their fundamental or overtone frequencies when other strings are sounded. For example, an A string at 440 Hz will cause an E string at 330 Hz to resonate, because they share an overtone of 1320 Hz (the third overtone of A and fourth overtone of E).

References

External links

resonance in Bosnian: Rezonanca
resonance in Bulgarian: Резонанс
resonance in Czech: Rezonance
resonance in Danish: Resonans (fysik)
resonance in German: Resonanz (Physik)
resonance in Estonian: Resonants
resonance in Spanish: Resonancia (mecánica)
resonance in French: Résonance
resonance in Korean: 공명
resonance in Croatian: Rezonancija
resonance in Italian: Risonanza (fisica)
resonance in Hebrew: תהודה
resonance in Lithuanian: Rezonansas
resonance in Hungarian: Rezonancia
resonance in Malay (macrolanguage): Resonan
resonance in Dutch: Resonantie
resonance in Japanese: 共鳴
resonance in Norwegian: Resonans
resonance in Polish: Rezonans
resonance in Portuguese: Ressonância
resonance in Russian: Резонанс
resonance in Slovenian: Resonanca
resonance in Finnish: Resonanssi
resonance in Swedish: Resonans
resonance in Thai: การสั่นพ้อง
resonance in Vietnamese: Cộng hưởng
resonance in Ukrainian: Резонанс
resonance in Chinese: 共振

Synonyms, Antonyms and Related Words

amplitude, antinode, crest, de Broglie wave, diffraction, electromagnetic radiation, electromagnetic wave, fluctuation, frequency, frequency band, frequency spectrum, guided wave, harmonic motion, in phase, interference, libration, light, longitudinal wave, mechanical wave, node, nutation, oscillation, out of phase, pendulation, period, periodic wave, periodicity, radio wave, ray, reinforcement, resonance frequency, seismic wave, shock wave, sound wave, surface wave, tidal wave, transverse wave, trough, vacillation, vibrancy, vibratility, vibration, wave, wave equation, wave motion, wave number, wavelength, wavering
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