Electromagnetic action

Figure 6. Illustrating electromagnetic action of the Lorentz force in a current-carrying conductor.

If we consider the picture of the London-Van Der Waals forces as given above, viz., as an attraction between the temporary dipole of one atom and the dipole induced by it of the second atom, the finite velocity of propagation of electromagnetic actions causes the induced dipole to be retarded against the inducing one by a time equal to rn/c (if r is the distance between the two atoms and n the refractive index of the medium for the frequency coupled with the temporary dipole). The reaction of the induced dipole on the first one again is retarded by the same time, and if in this total time-lag of 2rn/c the direction of the first dipole is altered by 90 ", the force exerted is exactly nullified, and by a change of 180 " even reverted from an attraction into a repulsion. 

Maxwell James Clerk (1831—1879) Brit, phys., validated kinetic theory of gases, applied dynamical equations in generalized Lagrangian form and showed that electromagnetic action travels through space in transverse waves, as does light, symmetrical (Maxwell) equations of continuous nature of electric and magnetic field used today (book Matter and Motion 1876)... 

Riemann George Friedrich Bernhard (1826-1866) Ger. math., introduced idea of finite but unbounded space (Riemann s functions and prime numbers), devised innovative geometry of the saddle-like space, theory of electromagnetic action Riga Alan T. (1937-) US chem.., polymers and pharmacy science, lubricants and biosensors (book Material characterization by TA 1991)... 

In 1821 Michael Faraday sent Ampere details of his memoir on rotary effects, provoking Ampere to consider why linear conductors tended to follow circular paths. Ampere built a device where a conductor rotated around a permanent magnet, and in 1822 used electric currents to make a bar magnet spin. Ampere spent the years from 1821 to 1825 investigating the relationship between the phenomena and devising a mathematical model, publishing his results in 1827. Ampere described the laws of action of electric currents and presented a mathematical formula for the force between two currents. However, not everyone accepted the electrodynamic molecule theory for the electrodynamic molecule. Faraday felt there was no evidence for Ampere s assumptions and even in France the electrodynamic molecule was viewed with skepticism. It was accepted, however, by Wilhelm Weber and became the basis of his theory of electromagnetism. 

Electromagnetic radiation energy can be used to stimulate substances to fluorescence after separation by thin-layer chromatography. Its action makes it possible to convert some nonfluorescent substances into fluorescent derivatives. The active sorbents often act as catalysts in such processes (cf. Chapter 1.1). 

X-rays High-energy electromagnetic radiation usually produced by the action of high-energy electrons hitting a solid target. 

If the effect of the temperature on reaction rate is well known, and is very easy to express, the problem is very different for effects of electromagnetic waves. What can be expected from the orienting action of electromagnetic fields at molecular levels Are electromagnetic fields able to enhance or modify collisions between reagents All these questions are raised by the use of microwaves energy in chemistry. 

When an electromagnetic wave interacts with resonators, the effect of quantization of all possible stationary stable oscillating amplitudes arises without the requirement of any specifically organized conditions (like the inhomogeneous action of external harmonic force). 

The Hamiltonian of helium, in the center of mass frame and under the action of an electromagnetic field polarized along the x axis, with field amplitude F and frequency w, reads, in atomic units,... 

Abstract This review reports on the study of the interplay between magnetic coupling and spin transition in 2,2 -bipyrimidine (bpym)-bridged iron(II) dinuclear compounds. The coexistence of both phenomena has been observed in [Fe(bpym)(NCS)2]2(bpym), [Fe(bpym)(NCSe)2]2(bpym) and [Fe(bt)(NCS)2]2(bpym) (bpym = 2,2 -bipyrimidine, bt = 2,2 -bithiazoline) by the action of external physical perturbations such as heat, pressure or electromagnetic radiation. The competition between magnetic exchange and spin crossover has been studied in [Fe(bpym)(NCS)2]2(bpym) at 0.63 GPa. LIESST experiments carried out on [Fe(bpym)(NCSe)2]2(bpym) and [Fe(bt)(NCS)2]2(bpym) at 4.2 K have shown that it is possible to generate dinuclear molecules with different spin states in this class of compounds. A special feature of the spin crossover process in the dinuclear compounds studied so far is the plateau in the spin transition curve. Up to now, it has not been possible to explore with a microscopic physical method the nature of the species... 

Gauging the Wess-Zumino term with to respect the electromagnetic interactions yields the familiar 7r° — 27 anomalous decay. This term [35] can be written compactly using the language of differential forms. It is useful to introduce the algebra-valued Maurer-Cartan one form a = a dx = (d U) U l dxF = (dU) U l which transforms only under the left SUp 3) flavor group. The Wess-Zumino effective action is... 

Let us assume an active medium that responds to the energy-level diagram of Figure 2.6(a). It consists into four energy levels E, with respective population densities M (i = 0,..., 3). Let us also assume that laser action can take place due to the stimulated emission process E2 Ei. When a monochromatic electromagnetic wave with frequency v, such as (E2 — E )lh = v, travels in the z direction through the medium, the intensity of the beam at a depth z into the crystal is given by... 

Figures 2.13(a) and 2.13(b) illustrate the basis of a semiconductor diode laser. The laser action is produced by electronic transitions between the conduction and the valence bands at the p-n junction of a diode. When an electric current is sent in the forward direction through a p-n semiconductor diode, the electrons and holes can recombine within the p-n junction and may emit the recombination energy as electromagnetic radiation. Above a certain threshold current, the radiation field in the junction becomes sufficiently intense to make the stimulated emission rate exceed the spontaneous processes.

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