Light, wave theory

Valence bond and molecular orbital theory both incorporate the wave description of an atom s electrons into this picture of H2 but m somewhat different ways Both assume that electron waves behave like more familiar waves such as sound and light waves One important property of waves is called interference m physics Constructive interference occurs when two waves combine so as to reinforce each other (m phase) destructive interference occurs when they oppose each other (out of phase) (Figure 2 2) Recall from Section 1 1 that electron waves m atoms are characterized by their wave function which is the same as an orbital For an electron m the most stable state of a hydrogen atom for example this state is defined by the Is wave function and is often called the Is orbital The valence bond model bases the connection between two atoms on the overlap between half filled orbifals of fhe fwo afoms The molecular orbital model assembles a sef of molecular orbifals by combining fhe afomic orbifals of all of fhe atoms m fhe molecule... 

The refractive index of a substance is, of course, a relative expression, as it refers to a second substance, which, in ordinary determinations, is always the air. The term refractive index indicates the ratio of the velocities with which light traverses the two media respectively. This is, as is easily demonstrated by a consideration of the wave theory of light, identical with the ratio of the sine of the angle of incidence, and the sine of the angle of refraction, thus—... 

Dutch mathematician Christiaan Huygens first states his wave theory of light, published in Traite de la lumiere in 1690. 

The wave theory for light provides a satisfactory explanation for these observations. It was, indeed, this very experiment conducted by T. Young (1802) that, in the nineteenth century, led to the replacement of Newton s particle theory of light by a wave theory. 

The harmonic oscillator is an important system in the study of physical phenomena in both classical and quantum mechanics. Classically, the harmonic oscillator describes the mechanical behavior of a spring and, by analogy, other phenomena such as the oscillations of charge flow in an electric circuit, the vibrations of sound-wave and light-wave generators, and oscillatory chemical reactions. The quantum-mechanical treatment of the harmonic oscillator may be applied to the vibrations of molecular bonds and has many other applications in quantum physics and held theory. 

Rayleigh,1902. Wave theory of light. In Scientific Papers by John William Strutt, Baron Rayleigh, vol. 3. Cambridge University Press, Cambridge, UK, 47-189... 

Kelvin, Lord, Baltimore Lectures on Molecular Dynamics and the Wave Theory of Light. C. J. Clay and Sons, London, 1904, Appendix H, pp. 602-642. 

The fifth consequence of the theory is that the adsorptivity and catalytic activity of a semiconductor are affected by illumination. When a crystal absorbs light waves of photoelectrically active frequencies (i.e., frequencies exciting the internal photoeffect), this leads, generally speaking, to a change... 

Fresnel, Augustin Jean (1788—1827). A French physicist noted for his work on optics, such as aberration of light, interference, wave theory of light, etc. He constructed the first practical "interferometer", which is used at present in modified form in Ordnance, such as "interferometric analysis of air flow about projectiles In free flight"... 

W.T. Kelvin, Baltimore lectures on molecular dynamics and the wave theory of light. C.J. Clay, London, 1904. 

We shall apply the time-dependent perturbation theory of the last section to a system exposed to electromagnetic radiation. Before doing so, we review the classical wave theory of light.2... 

The wave aspects of the photon are completely described by charge-frcc Maxwell equations. Therefore, it is natural to try to reconcile Planck s hypothesis with the wave theory of light. 

By 1903. llie wave theory of light based oil Maxwell s equations was well established, but certain phenomena would not fit in. It seemed that emission and absorption of hght occur discontinuously. This led Einstein to (lie view that the energy is concentrated in discrete particles. It was a revolutionary idea, very hard to understand, as the successes of the wave theory were undeniable. It seemed that light had to be understood sometimes as waves, sometimes as particles, and physicists had to get used to it, The idea was incorporated into Bohr s theory of the hydrogen atom and forms an essential part of it. 

A full explanation of the properties of light requires both the wave theory of electromagnetic radiation and the quantum theory. Most photochemical processes are best understood in terms of the quantum theory, which says that light is made up of discrete particles called quanta or photons. Each quantum carries an amount of energy, S, determined by the wavelength of the light, A. Equation 13.1, in which h is Planck s constant and c is the speed of light in a vacuum,... 

In 1900 Max Planck proposed a solution to the problem of black-body radiation described above. He suggested that when electromagnetic radiation interacts with matter, energy can only be absorbed or emitted in certain discrete amounts, called quanta. Planck s theory will not be described here, as it is highly technical. In any case, Planck s proposal was timid compared with the theory that followed. He supposed that quanta were only important in absorption and emission of radiation, but that otherwise the wave theory did not need to be modified. It was Einstein who took a more radical step in 1905 (the year in which he published his first paper on the theory of relativity and on several other unrelated topics). Einstein s analysis of the photoelectric effect is crucial, and has led to a complete change in the way we think of light and other radiation. 

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