Resonance Definition: Term in chemistry used to explain properties of the octet rule when a single Lewis structure is inadequate. Resonance structure is an average of. The Resonance Science Foundation is dedicated to advancing the research and education of Unified Physics and the unification of all sciences in alignment with a.
Article about resonance by The Free Dictionary(also mesomerism), the nature of the distribution of molecular electron density that may be considered as a partial delocalization of the bonds and atomic charges. Thus, according to the classical structure of the carboxylate anion, one of the oxygen atoms is bonded to the carbon atom by a single bond and carries a full negative charge, whereas the other is connected by a double bond and is neutral. Such a structure (see below) may be given by two equivalent formulas (I) and (II). However, experiment has shown that the oxygen atoms are identical—that is, each atom bears the same partial negative charge, and both bonds to the carbon atom are identical in length. Thus, the actual structure is intermediate between (I) and (II) and may be given as a resonance hybrid of canonical (extreme) structures (I) and (II) or as the resonance structure (III), in which the curved arrows indicate the direction of the electron shifts leading to equalization of the charges and bonds: Resonance is clearly manifested in conjugate systems. It usually expresses a state that is intermediate between the classical structure and a structure (or structures) with complete charge separation—for example,In cyclic conjugate systems, a resonance shift does not always lead to charge separation.
Another common physics demonstration that serves as an excellent model of resonance is the famous "singing rod" demonstration. A long hollow aluminum rod is held at. The above excerpt was read by Hélène Cardona at the Los Angeles Times Festival of Books, april 22th, 2017. Beyond Elsewhere by Gabriel Arnou-Laujeac, translated by. Resonance for An Introduction to Chemistry by Mark Bishop. A reasonable Lewis structure for the nitrate polyatomic ion, NO 3 In sound applications, a resonant frequency is a natural frequency of vibration determined by the physical parameters of the vibrating object.
Thus, the benzene structure may be given as a resonance hybrid of two classical Kekul. Chemical substituents with an unshared electron pair (R2. N—, R. A quantitative picture of the electron density distribution in molecules may be obtained from quantum- mechanical calculations. The idea of resonance was developed mainly by the English chemist C. Ingold in 1. 92. 6. REFERENCENesmeianov, A. Nachala organicheskoi khimii, book 1.
DIATKINthe phenomenon of a marked increase in the amplitude of forced oscillations, occurring in an oscillatory system when the frequency of an external periodic force approaches certain values that are determined by the inherent properties of the system. In the simplest cases, resonance occurs when the frequency of the external force approaches one of the frequencies at which natural oscillations occur as a result of an initial impulse. The nature of the resonance phenomenon is essentially dependent on the properties of the oscillatory system.
Resonance, An object free to vibrate tends to do so at a specific rate called the object's natural, or resonant, frequency. Hi everyone, I am Resonance22 and my goal is to help make Strategy games easy to learn. I am a top ranked Age of Empires II HD player. Some of you may know m.
Resonance definition, the state or quality of being resonant.
The simplest resonance occurs in a system subjected to a periodic force when the system’s parameters are not a function of the state of the system itself (a linear system). Figure 1. Mechanical oscillatory system.
The characteristic features of resonance can be seen in the case of a harmonic force acting on a system having one degree of freedom, such as a mass m suspended on a spring and subjected to a harmonic force F = F0 cos . Although the following remarks refer specifically to the first of these models, the explanation can be extended to apply to the second model as well. We will assume that the spring obeys Hooke’s law (this assumption is necessary if the system is to be linear); that is, the force acting from the spring side on the mass m is equal to kx, where x is the displacement of the mass from its equilibrium position and k is the modulus of elasticity.
For the sake of simplicity, the force of gravity is not taken into consideration. Furthermore, assume that when the mass is in motion, it experiences a resistance from the surrounding medium that is proportional to. Figure 2. Electrical oscillatory system with capacitance C and inductance L connected in seriesthe velocity x. This is necessary so that the system will remain linear.
Then the equation of motion for the mass m when an external harmonic force F is present has the form(1) mx. The first solution corresponds to the natural oscillations of the system that occur as a result of the action of an initial impulse, and the second solution corresponds to the forced vibrations. As a result of the presence of friction and the resistance of the medium, the natural oscillations are always damped; therefore, over a sufficiently long period of time (the less the damping of the natural oscillations, the longer the time) only certain forced oscillations will continue in the system. The solution corresponding to the forced oscillations has the form. Here,Thus, the forced oscillations are harmonic oscillations having a frequency equal to that of the external force.
The amplitude and phase of the forced oscillations depend on the relationship between the frequency of the external force and the system’s parameters. The dependence of the displacement amplitude of the forced oscillations on the relationship between the values of the mass m and the elasticity k can best be seen if one assumes that m and k remain constant while the frequency of the external force is varied.
When the frequency is very low (. With a further increase in . Displacement amplitudes as a function of the frequency of an external force for various values of b (b. On the other hand, when the damping in the system is increased, the resonance becomes less and less marked, and if b is very large, then the resonance is no longer noticeable. In terms of energy, resonance is accounted for by the phase relationships between the external force and the forced oscillations that deliver the most power to the system, because the velocity of the system is found to be in phase with the external force and thus creates the most favorable conditions to stimulate forced oscillations. If a periodic but nonharmonic external force acts on a linear system, then resonance occurs only when the external force contains harmonic components with a frequency close to a natural frequency of the system. In this case, the phenomenon discussed above will proceed for each individual component.
If there are several of these harmonic components with frequencies close to a natural frequency of the system, then each of them will produce resonance phenomena, and, in accordance with the principle of superposition, the total effect will be equal to the sum of the effects from the individual harmonic components. If, however, there are no harmonic components in the external force at frequencies close to a natural frequency of the system, then no resonance will occur. Thus, a linear system proves to be resonant only when the external force is harmonic. Figure 4. Electrical oscillatory system with capacitance and inductance connected in parallel.
In electrical oscillatory systems composed of a capacitance C connected in series with an inductance L (Figure 2) resonance occurs as follows: when the frequency of the external electromotive force (emf) approaches a natural frequency of the oscillatory system, the amplitudes of the emf across the coil and the voltage on the capacitor taken separately are much greater than the amplitude of the emf created by the source; but the emf across the coil and the voltage on the capacitor are equal to each other in magnitude and opposite in phase. When a harmonic emf acts on a network having a capacitance connected in parallel with an inductance (Figure 4), a special case of resonance occurs—an antiresonance. As the frequency of the external emf approaches the natural frequency of the LC circuit, the amplitude of the forced oscillations in the circuit does not increase; rather, the amplitude of the current in the external net- Figure 5. Example of two coupled electrical circuitswork feeding the circuit is sharply reduced. In electrical engineering, this phenomenon is called current resonance or parallel resonance. It is attributable to the fact that when the frequency of an external force is close to the natural frequency of the circuit, the reactances of both parallel branches (capacitive and inductive) become identical in magnitude so that the currents in both branches are of approximately the same amplitude but almost opposite in phase.
As a result, the amplitude of the current in the external network, which is the algebraic sum of the currents in the individual branches, proves to be much lower than the current amplitudes in the individual branches, which reach their highest values with parallel resonance. As is the case with a series resonance, a parallel resonance increases with a decrease in the active resistance in the branches of the resonant circuit. Series and parallel resonances are known as voltage and current resonances, respectively.
In a linear system having two degrees of freedom, particularly in the case of two coupled systems (for example, in the two coupled electrical circuits in Figure 5), the phenomenon of resonance retains the basic features indicated above. However, because the natural oscillations in a system having two degrees of freedom may occur at two different frequencies (the normal frequencies), resonance occurs when the frequency of a harmonic external force coincides with either one of the system’s normal frequencies.
Therefore, if the system’s normal frequencies are not very close to one another, two maxima will be observed in the amplitude of the forced oscillations (Figure 6) as the frequency of the external force is continuously varied. However, if the system’s normal frequencies are close to each other and the system’s damping is sufficiently high so that the resonance at each of the normal frequencies is attenuated, the two maxima may coincide. In this case, the resonance curve for a system having two degrees of freedom loses its “double- humped” character and differs little in appearance from the resonance curve of a linear circuit having one degree of freedom. Thus, the shape of the resonance curve for a system with two degrees of freedom not only depends on the circuit’s damping, as is the case of a system with one degree of freedom, but also on the degree of coupling between the circuits. Figure 6. Resonance curve with two maxima. Coupled systems also exhibit a phenomenon that is to a certain extent analogous to the phenomenon of antiresonance in a system with one degree of freedom.