Light

2009-02-11T02:38:35Z

ChuckTimton: mentions theory of

The theory of '''Light''' refers to [[electromagnetic]] [[radiation]] of any [[wavelength]], or to EM radiation of visible wavelengths <ref>Wavelengths of EM spectrum <i>usbyte.com</i> [http://www.usbyte.com/common/approximate_wavelength.htm]</ref> ; that stimulate the [[organ]]s of sight, having for normal human vision wavelengths ranging from about 3900 to 7700 [[ångstrom]]s (390 to 780 [[nm]]), violet has the shortest wavelength and red has the largest.
It travels at the [[speed of light]]: about 186,300 [[mile]]s (300,000 kilometres) per second.

EM radiation is a disturbance in an [[electric field]], it consists of an energy particle called a "[[photon]]", a photon carries no [[electric charge]] and is [[mass]]less, but since all energy is attracted by gravitation, light rays will bend near planets and stars.

Debate over whether light was a wave, or consists of particles was finally solved when [[quantum physics]] revealed all particles have wavelengths, but this is not generally noticeable in normal matter.

The EM spectrum consists of the following types of photon radiation (in order of increasing wavelength): [[gamma ray]]s, [[x-ray]]s, [[ultraviolet light]], [[visible light]], [[infrared light]], [[microwaves]] and [[radio waves]].

The [[Michelson-Morley experiment]] proved that the speed of light (and everything else that is massless) will always be measured by an observer to be the same, in every frame of reference, no matter how fast the source or the observer are moving, this gives rise to the [[theory of relativity]].

As with any wave, wavelength times frequency equals the speed of a light wave.

In the Biblical creation God created light on the first [[day]]; [[God]] said ''Let there be light,'' and there was light<ref>[[Genesis]] 1:3</ref>.

== Creationism and starlight ==
{{main|Starlight problem}}

A common criticism of the [[young Earth Creationism|young-Earth creationist]] viewpoint is that if the universe is only 6,000 years old, how would starlight from more than 6,000 light years away have reached Earth?

Young-Earth creationists have proposed a number of solutions to this problem, the current most popular explanations involving time dilation fields which resulted in billions of years time passing in outer space while only 6,000 years passed on Earth.

Young-Earth creationists have also pointed out that the [[Big Bang theory|big bang theory]] has its own starlight travel problem, known as the [[horizon problem]].

==References==
<references/>

[[Category:Physics]]

Electricity

2009-02-11T02:36:33Z

ChuckTimton: Added theory of

[[Image:Htryt5.jpg|right|thumb|200px|Lightning strikes during a night-time thunderstorm. Energy is radiated as light when powerful electric currents flow through the Earth's atmosphere.]]
The theory of '''Electricity''' is [[energy]] that can be converted to heat, light, motion and many other physical effects through the force produced in the attraction or repulsion between charged particles. It is measured in terms of [[electrical charge]], [[current]], [[voltage]], and [[resistance]]. A basic element of electricity is the electric circuit. A circuit is a closed path that allows for movement of charges. Current is the name given to the movement of charges. The study of electricity involves the behavior of charges, current and voltage with the components that make up the electrical circuit. Electrical engineering has allowed many practical advances to be made, such as replacing [[steam power]]ed trains with more efficient electric or nuclear ones.

==Polarity==

All materials that are known contain two basic components of electric charge: the [[proton]] and the [[electron]]. The proton is a particle with a single positive charge, and the electron has a single negative charge.

It is the arrangement of electrons and protons as basic particles of electricity that determines the electrical characteristics of substances. Although all matter has protons and electrons, most materials do not exhibit any evidence of electrical activity, because the protons and electrons arranged in balanced ways. In order to use electricity to do work, the material must contain electrons that are free to move from atom to atom. A battery can do electrical work because a chemical process takes place when it is part of a completed circuit moves electrons towards its negative terminal and conversely, creates a lack of them at its positive terminal. Electrons then flow through the circuit to keep balancing out this chemical process.

Some molecules are said to be "polarized" because their atomic arrangement and electron sharing causes a net charge to develop on opposite sides. Water is a classic example of this, with the electrons from the [[hydrogen]] atoms "spending more time" in proximity to the [[oxygen]] atoms. Since the hydrogen atoms are "attached" to the oxygen asymmetrically (instead of being at opposite sides of the oxygen, the angle between their "attachment points" is 108 degrees), one end of the water molecule carries a positive charge and the other a negative one. This polarization results in water's ability to dissolve [[salt]]s, and display acidic or basic characteristics.

==The Structure of an Atom Determines its Electrical Characteristics==

Although there are many possible ways protons and electrons could group themselves, they assemble in specific combinations that result in stable arrangement. Each stable arrangement of protons, electrons, and often [[neutron]]s makes one particular kind of atom, an [[element]]. Electrons orbit the nucleus of protons and neutrons at specific intervals, called "shells" or "energy levels." Each shell has a maximum number of electrons for stability.
It is the structure of the outermost shell of electrons in an element that determines how well it conducts electricity and its magnetic properties. If an element has fewer than eight electrons in its outermost shell, for example helium which has only two electrons, then it can conduct electricity to some degree; the elements that have one electron in their outermost shell conduct electricity best. [[Gold]], [[silver]], and [[copper]] are the best conductors of electricity because their outermost electron shell has only one electron, and this allows the freest flow of electrical current because the opposition of an atom of these elements from taking on or loosing electrons is low.
Materials with electrons that tend to stay in their own orbits are called insulators, because they do not conduct electricity very well. However, these materials (except for the inert gases) can also take up extra electrons to complete their outer shells, and become negatively charged; they hold on to and store electrical charge, unlike conductors. Insulating materials like glass, plastic, rubber, paper, air, and mica are called dielectrics, meaning that they can take on and hold electrical charge. Insulators are useful when it is necessary to prevent current flow. They are also used in applications for storing electrical charge, as in capacitors, since a good conductor of electricity cannot store any charge.
Materials that can conduct more electrical charge than insulators, but less than conductors are called semiconductors. [[Carbon]], [[silicon]], and [[germanium]] are commonly used for transistors and other semiconductor components, with silicon being the most widely used.

==Resources==
Grob, Bertand ''Basic Electronics'' Fifth edition, 1984

[[Category:Physics]]
[[Category:Electricity]]

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Light

Electricity