• Choose a category
• All
• Classic-Fiction

By Root 411 0

They are wave packets. Sometimes they behave as waves (light diffraction from a grating and electron diffraction from a crystal surface) and sometimes they behave as particles (photons in the photoelectric effect and electrons in the cathode ray tube of old-style televisions). In fact, the essence of the nature of absolutely small particles is that they are really neither particles nor waves but a strange type of entity that has simultaneously particle and wave properties. This duality of matter is contained in the Heisenberg Uncertainty Principle. In contrast to a classical object like a baseball, we cannot know exactly simultaneously the position and the momentum (mass times velocity) of an electron or other absolutely small particles.

When is a particle absolutely small and subject to the new world of quantum physics? Dirac taught us that there is a minimum disturbance that accompanies a measurement, a disturbance that is inherent in the nature of things and can never be overcome by improved experimental technique. If the disturbance is negligible, then the object is large in an absolute sense, and it can be described by class physics. However, if the minimum disturbance accompanying a measurement is nonnegligible, then the object is absolutely small, and its properties fall in the realm of quantum mechanics. The quantum properties of absolutely small particles are not strange; they are just unfamiliar and not subject to our classical intuition. They are like the moon to the toddler. In this book the fundamental concepts of quantum theory have been explicated and applied to some important everyday phenomena. You are no longer a quantum toddler.

Glossary

absolute size—An object is large or small not by comparison to another object, but rather by comparison to the intrinsic minimum disturbance that accompanies a measurement. If the disturbance is negligible, the object is large in an absolute sense. If the intrinsic minimum disturbance is nonnegligible, the object is absolutely small.

absorption of light—The process by which the amount light is reduced, and the energy of an object is increased. Light (photons, particles of light) of the proper frequency (color) will cause the quantum state of an object to go to a higher energy state. The increase in energy of the object exactly matches the decrease in energy of the light. Absorption of light by objects is responsible for their color.

ångström—A unit of length that is 10-10 m (one ten billionth of a meter). The ångström unit has the symbol, Å.

anion—A negatively charged atom or molecule, such as Cl-, the chloride anion. An anion is formed by adding one or more negatively charged electrons to a neutral atom or molecule.

atomic number—The number of protons (positively charged particles) in an atomic nucleus. A neutral atom (not an ion) has the same number of electrons (negatively charged particles) as protons.

atomic orbital—The name given a wavefunction (probability amplitude wave) that describes the probability distribution of an electron about an atomic nucleus.

black body radiation—The light given off by a hot object. The colors of the light depend on the temperature of the object. Black body radiation is the first physical phenomenon described with the ideas that became quantum mechanics by Max Planck in 1900.

Born interpretation—The description of quantum mechanical wavefunctions as probability amplitude waves. The Born interpretation, also referred to as the Copenhagen interpretation, states that the quantum mechanical wavefunctions obtained from solving the Schrödinger equation describe the probability of finding a particle in some region of space.

cation—a positively charged atom or molecule, such as Na+, the sodium cation. A cation ion is formed by removing one or more negatively charged electrons from a neutral atom or molecule.

classical mechanics—The theory of matter and light that was developed before the advent of quantum mechanics. It treats size as relative and cannot describe absolutely small particles (electrons, photons, etc.). It is a