Arus listrik: Béda antarrépisi
Konten dihapus Konten ditambahkan
m Ngarapihkeun éjahan, replaced: dimana → di mana, kucara → ku cara using AWB |
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== Définisi ==
Gedéna arus listrik diséfinisikeun minangka [[turunan wanci]] ti [[muatan listrik]]:
:<math>I = {dQ \over dt}</math>
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:<math>v \!\ </math> is the drift velocity, and
:<math>Q \!\ </math> is the charge on each particle.
Electric currents in solid matter are typically very slow flows. For example, in a [[copper]] [[wire]] of cross-section 0.5 mm², carrying a current of 5 A, the ''[[drift velocity]]'' of the electrons is of the order of a millimetre per second. To take a different example, in the near-vacuum inside a [[cathode ray tube]], the electrons travel in near-straight lines ("ballistically") at about a tenth of the [[speed of light]].
However, we know that electrical [[Signal (information theory)|signals]] are [[electromagnetic]] waves which propagate at very high speed (at the speed of light, as can be deduced from [[Maxwell's Equations]]). For example, in [[electric power transmission|AC power lines]], the waves of electromagnetic energy propagate rapidly through the space between the wires from a source to a distant [[external electric load|load]], even though the electrons in the wires only move back and forth over a tiny distance. Although the velocity of the flowing charges is quite low, the associated electromagnetic energy travels at the speed of light. The ratio of the [[signal velocity]] through a medium versus the speed of light in a vacuum is called the [[velocity factor]].
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== Hukum Ohm ==
[[Hukum Ohm]] ngira-ngira arus dina [[résistor]] (idéal) (atawa [[alat ohmik]] séjénna)
:<math>
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</math>
di mana
:''I'' nyaéta arus, diukur dina [[ampere]]
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== Arus konvénsional ==
Conventional current was defined early in the history of electrical science as a flow of positive charge. In solid metals, like wires, the positive charges are immobile, and only the negatively charged [[electron]]s flow in the direction opposite conventional current, but this is not the case in most non-metallic conductors. In other materials, charged particles flow in both directions at the same time. Electric currents in [[electrolytes]] are flows of electrically charged atoms ([[ion]]s), which exist in both positive and negative varieties. For example, an [[electrochemistry|electrochemical]] cell may be constructed with salt water (a solution of [[sodium chloride]]) on one side of a membrane and pure water on the other. The membrane lets the positive sodium ions pass, but not the negative chlorine ions, so a net current results. Electric currents in [[Plasma physics|plasma]] are flows of electrons as well as positive and negative ions. In ice and in certain solid electrolytes, flowing [[proton]]s constitute the electric current. To simplify this situation, the original definition of conventional current still stands.
There are also instances where the electrons are the charge that is moving, but where it makes more sense to think of the current as the movement of positive "[[electron hole|holes]]" (the spots that should have an electron to make the conductor neutral). This is the case in a p-type [[semiconductor]].
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== Kaamanan Listrik ==
The most obvious hazard is electric shock, where a current through part of the body can cause effects from a slight tingle to [[cardiac arrest]] or severe [[burns]]. It is the current that passes that determines the effect, and this depends on the nature of the contact, the condition of the body part, the current path through the body and the voltage of the source. The effect also varies considerably from individual to individual. (For approximate figures see '''Shock Effects''' under [[electric shock]].)
Due to this and the fact that passing current cannot be easily predicted in most practical circumstances, any supply of over 50 volts should be considered a possible source of dangerous electric shock. In particular, note that 110 volts (a minimum voltage at which AC [[mains electricity|mains]] power is [[List of countries with mains power plugs, voltages and frequencies|distributed in many countries]]) can certainly be lethal.
Electric arcs, which can occur with supplies of any voltage (for example, a typical [[arc welding]] machine has a voltage between the [[electrode]]s of just a few tens of volts), are very hot and emit [[ultra-violet]] (UV) and [[infra-red radiation]] (IR). Proximity to an electric arc can therefore cause severe thermal burns, and UV is damaging to unprotected eyes and skin.
Accidental electric heating can also be dangerous. An overloaded [[power cable]] is a frequent cause of fire. A battery as small as an [[AA cell]] placed in a pocket with metal coins can lead to a short circuit heating the battery and the coins which may inflict burns. [[Nickel-cadmium battery|NiCad]], [[Nickel metal hydride battery|NiMh cells]], and [[Lithium battery|Lithium batteries]] are particularly risky because they can deliver a very high current due to their low [[internal resistance]].
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