In phase

A periodic signal (usually electromagnetic in nature) is in phase with another signal when both begin their cycle simultaneously. Whether the term is hyphenated or not depends on its use:
- "the in-phase signals prevent distortion"
- "the two signals are in phase with each other" See also: out of phase, phase difference Category:Wave mechanics

Periodicity

Periodicity is the quality of occurring at regular intervals (e.g. of time) and can occur in different contexts:
- A clock marks time at periodic intervals.
- A metronome ticks at periodic intervals.
- A publication published at periodic intervals can be called a "periodical", though it can also be called magazine.
- In mathematics, a function which recurs periodically is called periodic function.
- In chemistry, a table which classifies elements by means of periodicity is the periodic table. The measure of periodicity is frequency.

Electromagnetic

Electromagnetism is the physics of the electromagnetic field: a field, encompassing all of space, which exerts a force on those particles that possess a property known as electric charge, and is in turn affected by the presence and motion of such particles. The term electrodynamics is sometimes used to refer to the combination of electromagnetism with mechanics, and deals with the effects of the electromagnetic field on the dynamic behavior of electrically-charged particles.

Electric and magnetic fields

It is often convenient to understand the electromagnetic field in terms of two separate fields: the electric field and the magnetic field. A non-zero electric field is produced by the presence of electrically charged particles, and gives rise to the electric force; this is the force that causes static electricity and drives the flow of electric charge (electric current) in electrical conductors. The magnetic field, on the other hand, can be produced by the motion of electric charges, or electric current, and gives rise to the magnetic force associated with magnets. The term "electromagnetism" comes from the fact that the electric and magnetic fields generally cannot be described independently of one another. A changing magnetic field produces an electric field (this is the phenomenon of electromagnetic induction, which underlies the operation of electrical generators, induction motors, and transformers). Similarly, a changing electric field generates a magnetic field. Because of this inter-dependence between the electric and magnetic fields, it makes sense to consider them as a single, theoretically coherent entity — the electromagnetic field. This unification, which was completed by James Clerk Maxwell, is one of the triumphs of 19th century physics. It had far-reaching consequences, one of which was the elucidation of the nature of light: as it turns out, what we think of as "light" is actually a propagating oscillatory disturbance in the electromagnetic field, i.e., an electromagnetic wave. Different frequencies of oscillation give rise to the different forms of electromagnetic radiation, from radio waves at the lowest frequencies, to visible light at intermediate frequencies, to gamma rays at the highest frequencies. The theoretical implications of electromagnetism led to the development of special relativity by Albert Einstein in 1905.

The electromagnetic force

The force that the electromagnetic field exerts on electrically charged particles, called the electromagnetic force, is one of the four fundamental forces. The other fundamental forces are the strong nuclear force (which holds atomic nuclei together), the weak nuclear force (which causes certain forms of radioactive decay), and the gravitational force. All other forces are ultimately derived from these fundamental forces. As it turns out, the electromagnetic force is the one responsible for practically all the phenomena one encounters in daily life, with the exception of gravity. Roughly speaking, all the forces involved in interactions between atoms can be traced to the electromagnetic force acting on the electrically charged protons and electrons inside the atoms. This includes the forces we experience in "pushing" or "pulling" ordinary material objects, which come from the intermolecular forces between the individual molecules in our bodies and those in the objects. It also includes all forms of chemical phenomena, which arise from interactions between electron orbitals.

Origins of electromagnetic theory

The scientist William Gilbert proposed, in his De Magnete (1600), that electricity and magnetism, while both capable of causing attraction and repulsion of objects, were distinct effects. Mariners had noticed that lightning strikes had the ability to disturb a compass needle, but the link between lightning and electricity was not confirmed until Franklin's proposed experiments (performed initially by others) in 1752. One of the first to discover and publish a link between man-made electric current and magnetism was Romagnosi, who in 1802 noticed that connecting a wire across a Voltaic pile deflected a nearby compass needle. However, the effect did not become widely known until 1820, when Ørsted performed a similar experiment. Ørsted's work influenced Ampère to produce a theory of electromagnetism that set the subject on a mathematical foundation. An accurate theory of electromagnetism, known as classical electromagnetism, was developed by various physicists over the course of the 19th century, culminating in the work of James Clerk Maxwell, who unified the preceding developments into a single theory and discovered the electromagnetic nature of light. In classical electromagnetism, the electromagnetic field obeys a set of equations known as Maxwell's equations, and the electromagnetic force is given by the Lorentz force law. One of the peculiarities of classical electromagnetism is that it is difficult to reconcile with classical mechanics, but it is compatible with special relativity. According to Maxwell's equations, the speed of light is a universal constant, dependent only on the electrical permittivity and magnetic permeability of the vacuum. This violates Galilean invariance, a long-standing cornerstone of classical mechanics. One way to reconcile the two theories is to assume the existence of a luminiferous aether through which the light propagates. However, subsequent experiments efforts failed to detect the presence of the aether. In 1905, Albert Einstein solved the problem with the introduction of special relativity, which replaces classical kinematics with a new theory of kinematics that is compatible with classical electromagnetism. In addition, Relativity theory shows that in moving frames of reference a magnetic field becomes an electrostatic field and vice versa; thus firmly showing that they are two sides of the same coin, and thus the term Electromagnetism.

Failures of classical electromagnetism

In another paper published in that same year, Einstein undermined the very foundations of classical electromagnetism. His theory of the photoelectric effect (for which he won the Nobel prize for physics) posited that light could exist in discrete particle-like quantities, which later came to be known as photons. Einstein's theory of the photoelectric effect extended the insights that appeared in the solution of the ultraviolet catastrophe presented by Max Planck in 1900. In his work, Planck showed that hot objects emit electromagnetic radiation in discrete packets, which leads to a finite total energy emitted as black body radiation. Both of these results were in direct contradiction with the classical view of light as a continuous wave. Planck's and Einstein's theories were progenitors of quantum mechanics, which, when formulated in 1925, necessitated the invention of a quantum theory of electromagnetism. This theory, completed in the 1940s, is known as quantum electrodynamics (or "QED"), and is one of the most accurate theories known to physics.

SI electricity units

References

-
-
-
-

External links

- [http://www.rmcybernetics.com/science/physics/electromagnetism_intro_electric_force.htm Introduction to Electromagnetism] From the basics to advanced level science
- [http://ocw.mit.edu/OcwWeb/Physics/8-02Electricity-and-MagnetismSpring2002/VideoLectures/index.htm MIT Video Lectures - Electricity and Magnetism] from Spring 2002. Taught by Professor Walter Lewin.
- [http://www.lightandmatter.com/area1book4.html Electricity and Magnetism] - an online textbook (uses algebra, with optional calculus-based sections)
- [http://www.plasma.uu.se/CED/Book/ Electromagnetic Field Theory] - an online textbook (uses calculus)
- [http://farside.ph.utexas.edu/teaching/em/em.html Classical Electromagnetism: An intermediate level course] - an online intermediate level texbook downloadable as PDF file ko:전자기학 ja:電磁気学

Phase difference

The phase difference between two signals of the same frequency can be thought of as a delay or advance in the start of one signal's cycle with respect to another. Consider a graph of a sinusoidal waveform with amplitude on the y or vertical axis and time on the horizontal or x axis. If signals A and B begin at zero, build to a high positive value, fall through zero, build to a high negative value and return to zero at exactly the same time, the signals are of the same frequency and are said to be in phase, i.e. there is no phase difference between them. Conversely, if there are two signals of the same frequency (same distance between zero crossings on the x axis) but one signal begins earlier and the other one begins at a later point, they are said to be out of phase by some amount, i.e. there is some time difference between the two signals. Phase difference is expressed in degrees from 0 to 360, or in radians. If the difference is 180 degrees then the two signals are said to be in antiphase: they are equal but opposite, and if added together will sum to zero. If the phase difference is 90 degrees then the signals are said to be in quadrature. Category:Wave mechanics

Category:Wave mechanics

Category:Waves Category:Partial differential equations th:Category:กลศาสตร์คลื่น

Principles of Theoretical Logic

Principles of Theoretical Logic is the translation into English of the seminal 1928 work of David Hilbert and Wilhelm Ackermann on the formalisation of logic, which is most well-known for introducing the now-standard formalisation of first-order logic in the Hilbert calculus. The text also dealt with propositional logic and the calculus of relations.

References

- David Hilbert and Wilhelm Ackermann (1928). Grundzüge der theoretischen Logik (Principles of Theoretical Logic). Springer-Verlag, ISBN 0-8218-2024-9.
- Hendricks, Neuhaus, Petersen, Scheffler and Wansing (eds.) (2004). First-order logic revisited. Logos Verlag, ISBN 3-8325-0475-3. This volume is the proceedings of the workshop FOL-75 commemorating 75 years of Hilbert and Ackermann's contribution. Category:History of logic Category:Mathematics books

statystyki Malaga accommodation backup software download wakacje jastrz�bia g�ra domeny

:: RELATED NEWS ::

CYKZ
Buttonville Municipal Airport or Toronto/Buttonville Municipal Airport, (ICAO CYKZ, IATA YKZ), is a medium-sized private airport in Buttonville Ontario, Canada, immediately northwest of Markham and 29 km north of T

YKZ
Buttonville Municipal Airport or Toronto/Buttonville Municipal Airport, (ICAO CYKZ, IATA YKZ), is a medium-sized private airport in Buttonville Ontario, Canada, immediately northwest of Markham and 29 km north of T

Nicobar district
Nicobar district is a district of India, one of two districts in the Indian Union Territory (UT) of Andaman and Nicobar Islands. The district's administrative territory encompasses all of the Nicobar Islands, which are located in the

Astronomical catalogs
In astronomy, many stars are referred to simply by catalogue numbers. There are a great many different star catalogues which have been produced for different purposes over the years, and this article covers only some of the more frequently quoted ones. Most of the recent catalogues are available in electronic format and can be freely downloaded from NASA's Astronomical Data Center and other places (see links at end).

Historical catalogues

Although no l

Vergina sun
The Vergina Sun or Star of Vergina is a sixteen-ray star symbol found in archaeological excavations in Vergina, Greece. It decorates the golden larnax found by Professor Manolis Andronikos in 1977 in the tombs of the kings of the ancient state of Ma

Fender Tucker
Fender Tucker has been a disk magazine editor and publisher, and a self-publisher of books. Tucker acquired his first name in high school, naming himself for his favorite guitar. Ironically, he played a Fender Stratocaster for only a few years before switching to the 1966 Gibson ES-335 which he still plays. He discovered computers in the early 1980s when the home computer was introduced and was