Electromagnetic radiation photoelectric effect

The complete definiteness of nature as described by classical mechanics was destroyed by the necessity of assigning an inertia to electromagnetic radiation (photoelectric effect)...We can do without particles but... 

In the course of his research on electromagnetic waves Hertz discovered the photoelectric effect. He showed that for the metals he used as targets, incident radiation in the ultraviolet was required to release negative charges from the metal. Research by Philipp Lenard, Wilhelm Hallwachs, J. J. Thomson, and other physicists finally led Albert Einstein to his famous 1905 equation for the photoelectric effect, which includes the idea that electromagnetic energy is quantized in units of hv, where h is Planck s con-... 

Studies of black-body radiation led to Planck s hypothesis of the quantization of electromagnetic radiation. The photoelectric effect provides evidence of the particulate nature of electromagnetic radiation. 

You can appreciate why scientists were puzzled The results of some experiments (the photoelectric effect) compelled them to the view that electromagnetic radiation is particlelike. The results of other experiments (diffraction) compelled them equally firmly to the view that electromagnetic radiation is wavelike. Thus we are brought to the heart of modern physics. Experiments oblige us to accept the wave-particle duality of electromagnetic radiation, in which the concepts of waves and particles blend together. In the wave model, the intensity of the radiation is proportional to the square of the amplitude of the wave. In the particle model, intensity is proportional to the number of photons present at each instant. 

Example H2(g) + Cl2(g) 2 HCl(g). photoelectric effect The emission of electrons from the surface of a metal when electromagnetic radiation strikes it. 

Photoelectric effect The effect produced when electromagnetic radiation knocks electrons out of a metal. Einstein used this phenomenon to show that light was quantized and came in energy packets called photons. 

To explain the photoelectric effect, Einstein (1905) postulated that light, or electromagnetic radiation, consists of a beam of particles, each of which travels at the same velocity c (the speed of light), where c has the value... 

Finally, in the early 20th century Albert Einstein explained the photoelectric effect based on quantized packets of electromagnetic radiation called photons. These quickly led to the familiar relationships of the energy of a photon,... 

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. 

The mathematical treatment of the Rutherford-Bohr atom was especially productive in Denmark and Germany. It led directly to quantum mechanics, which treated electrons as particles. Electrons, however, like light, were part of electromagnetic radiation, and radiation was generally understood to be a wave phenomenon. In 1924, the French physicist Prince Louis de Broglie (1892-1987), influenced by Einstein s work on the photoelectric effect, showed that electrons had both wave and particle aspects. Wave mechanics, an alternative approach to quantum physics, was soon developed, based on the wave equation formulated in 1926 by the Austrian-born Erwin Schrodinger (1887-1961). Quantum mechanics and wave mechanics turned out to be complementary and both were fruitful for an understanding of valence. 

Note that the mechanism of ion-pair formation by y particles is not the same as that by a or 0 particles. A y ray itself will not leave behind it a trail of ion pairs but rather collides with free or bound electrons imparting to them all or part of its electromagnetic energy (photoelectric and Compton effects). These secondary electrons are then responsible for formation of ion pairs in matter through which y radiation passes. In cases where the energy of radiation exceeds 1.02 Mev, another process is possible, the creation of electron->positron pairs. 

Electron emission. Many metals emit electrons when exposed to electromagnetic radiation. This is the famous photoelectric effect discussed in Chapter 1. Einsteins study of this effect led him to conclude that light could act as either wave or particle. 

Planck found it necessary to assume quantized energies to explain the radiation that heated bodies emit. Einstein s analysis of the photoelectric effect used Planck s concepts, suggesting that electromagnetic radiation is quantized. 23. 3.0 x 1010 s ... 

The interaction of ionizing electromagnetic radiation with matter is different from the processes previously mentioned, and the concept of ranges and specific ionization loss cannot be applied. Only the three most important absorption processes are considered the photoelectric effect, the Compton effect, and the pair-production effect. The corpuscular description of electromagnetic radiation is the most appropriate for these effects, as one photon in a well-collimated beam of photons disappears at each interaction. The attenuation of the photon beam can be described by a simple exponential law... 

A familiar device in modem technology is the photocell or electric eye, which mns a variety of useful gadgets, including automatic door openers. The principle involved in these devices is the photoelectric effect, which was first observed by Heinrich Hertz in the same laboratory in which he discovered electromagnetic waves. Visible or ultraviolet radiation impinging on clean metal surfaces can cause electrons to be ejected from the metal. Such an effect is not, in itself, inconsistent with classical theory since electromagnetic waves are known to carry energy and momentum. But the detailed behavior as a function of radiation frequency and intensity cannot be explained classically. 

In explaining the photoelectric effect, Albert Einstein proposed in 1905 that electromagnetic radiation has both wavelike and particlelike natures. That is, while a beam of light has many wavelike characteristics, it also can be thought of as a stream of tiny particles, or bundles of energy, called photons. Thus, a photon is a particle of electromagnetic radiation with no mass that carries a quantum of energy. 

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