Реферат: Физические законы, переменные, принципы
Pascal's principle
Pressure applied to an enclosed imcompressible static fluid istransmitted undiminished to all parts of the fluid.
Paschen series
The series which describes the emission spectrum of hydrogen whenthe electron is jumping to the third orbital. All of the linesare in the infrared portion of the spectrum.
Pauli exclusion principle (W. Pauli; 1925)
No two identical fermions in a system, such as electrons in anatom, can have an identical set of quantum numbers.
Peltier effect (J.C.A. Peltier; 1834)
The change in temperature produced at a junction between twodissimilar metals or semiconductors when an electric currentpasses through the junction.
permeability of free space ; magnetic constant; m 0
The ratio of the magnetic flux density in a substance to theexternal field strength for vacuum. It is equal to 4 p . 10-7 H/m.
permittivity of free space; electric constant; e0
The ratio of the electric displacement to the intensity of theelectric field producing it in vacuum. It is equal to 8.854 . 10-12 F/m.
Pfund series
The series which describes the emission spectrum of hydrogen whenthe electron is jumping to the fifth orbital. All of the linesare in the infrared portion of the spectrum.
Photoelectric effect
An effect explained by A. Einstein that demonstrate that lightseems to be made up of particles, or photons. Light can exciteelectrons (called photoelectrons) to be ejected from a metal.Light with a frequency below a certain threshold, at anyintensity, will not cause any photoelectrons to be emitted fromthe metal. Above that frequency, photoelectrons are emitted inproportion to the intensity of incident light. The reason is that a photon has energy in proportion to itswavelength, and the constant of proportionality is Planck'sconstant. Below a certain frequency -- and thus below a certainenergy -- the incident photons do not have enough energy to knockthe photoelectrons out of the metal. Above that threshold energy,called the workfunction, photons will knock the photoelectrons outof the metal, in proportion to the number of photons (theintensity of the light). At higher frequencies and energies, thephotoelectrons ejected obtain a kinetic energy corresponding tothe difference between the photon's energy and the workfunction.
Planck constant; h
The fundamental constant equal to the ratio of the energy of aquantum of energy to its frequency. It is the quantum of action.It has the value 6.626196 . 10-34 J . s.
Planck's radiation law
A law which more accurately described blackbody radiation becauseit assumed that electromagnetic radiation is quantized.
Poisson spot (S.D. Poisson)
See Arago spot. Poisson predicted the existence of such a spot,and actually used it to demonstrate that the wave theory of lightmust be in error.
Principle of causality
The principle that cause must always preceed effect. Moreformally, if an event A ("the cause") somehow influences an eventB ("the effect") which occurs later in time, then event B cannotin turn have an influence on event A. The principle is best illustrated with an example. Say thatevent A constitutes a murderer making the decision to kill hisvictim, and that event B is the murderer actually committing theact. The principle of causality puts forth that the act ofmurder cannot have an influence on the murderer's decision tocommit it. If the murderer were to somehow see himself committingthe act and change his mind, then a murder would have beencommitted in the future without a prior cause (he changed hismind). This represents a causality violation. Both time traveland faster-than-light travel both imply violations of causality,which is why most physicists think they are impossible, or atleast impossible in the general sense.
Principle of determinism
The principle that if one knows the state to an infinite accuracyof a system at one point in time, one would be able to predict thestate of that system with infinite accuracy at any other time,past or future. For example, if one were to know all of thepositions and velocities of all the particles in a closed system,then determinism would imply that one could then predict thepositions and velocities of those particles at any other time.This principle has been disfavored due to the advent of quantummechanics, where probabilities take an important part in theactions of the subatomic world, and the Heisenberg uncertaintyprinciple implies that one cannot know both the position andvelocity of a particle to arbitrary precision.
Rayleigh criterion; resolving power