Electric Current - The Speed Of An Electric Current, Electric Current And Energy, Electric Current And Magnetism, Alternating Current - Current and the transfer of electric charge, Direct current
Electric current is the result of the relative motion of net electric charge. In metals, the charges in motion are electrons. The magnitude of an electric current depends upon the quantity of charge that passes a chosen reference point during a specified time interval. Electric current is measured in amperes, with one ampere equal to a charge-flow of one coulomb per second.
A current as small as a picoampere (one-trillionth of an ampere) can be significant. Likewise, artificial currents in the millions of amperes can be created for special purposes. Currents between a few milliamperes to a few amperes are common in radio and television circuits. An automobile starter motor may require several hundred amperes.
The total charge transferred by an unvarying electrical current equals the product of current in amperes and the time in seconds that the current flows. If one ampere flows for one second, one coulomb will have moved in the conductor. If a changing current is graphed against time, the area between the graph's curve and the time axis will be proportional to the total charge transferred.
A current in one direction only is called a direct current, or DC. A steady current is called pure DC. If DC varies with time it is called pulsating DC.
Additional Topics
Electrical currents move through wires at a speed only slightly less than the speed of light. The electrons, however, move from atom to atom more slowly. Their motion is more aptly described as a drift. Extra electrons added at one end of a wire will cause extra electrons to appear at the other end of the wire almost instantly. Individual electrons will not have moved along the length of the wire …
Heat results when current flows through an ordinary electrical conductor. Common materials exhibit an electrical property called resistance. Electrical resistance is analogous to friction in a mechanical system. Resistance results from imperfections in the conductor. When the moving electrons collide with these imperfections, they transfer kinetic energy, resulting in heat. The quantity of heat en…
A magnetic field is created in space whenever a current flows through a conductor. This magnetic field will exert a force on the magnetic field of other nearby current-carrying conductors. This is the principle behind the design of an electric motor. An electrical generator operates on a principle similar to an electric motor. In a generator, mechanical energy forces a conductor to move through a …
If a current changes direction repeatedly it is called an alternating current, or AC. Commercial electrical power is transported using alternating current because AC makes it possible to change the ratio of voltage to current with transformers. Using a higher voltage to transport electrical power across country means that the same power can be transferred using less current. For example, if transf…
We cannot directly observe the electrically-charged particles that produce current. It is usually not important to know whether the current results from the motion of positive or negative charges. Early scientists made an unfortunate choice when they assigned a positive polarity to the charge that moves through ordinary wires. It seemed logical that current was the result of positive charge in mot…
Citing this material
Please include a link to this page if you have found this material useful for research or writing a related article. Content on this website is from high-quality, licensed material originally published in print form. You can always be sure you're reading unbiased, factual, and accurate information.
Highlight the text below, right-click, and select “copy”. Paste the link into your website, email, or any other HTML document.
User Comments Add a comment…