For an explanation, see the main splats page

The principles of electrodynamics

• An electric current is a flow of electrons along a conductor which happens when there is a higher charge at one end of the conductor, compared with the other.

• When an electric current flows in a conductor, there will be an associated magnetic force near the conductor, and this force can be used in a variety of ways.

• An electrical current requires a potential difference and a conductor or conducting medium through which electrons can flow with little interference.

• A current may be thought of as a flow of electrons in one direction, or a flow of holes in the other. Each can be used to understand electric currents.

• A varying magnetic force or field near a conductor makes electrons in the conductor move, producing an electric current. This is the basis of the generator.

• Dynamic electricity (an ordinary electric current) may be generated by electromagnetic induction, a magnetic field inducing a flow of electrons in a conductor.

• An electrical current may be generated by chemical reactions in a 'dry cell', a form of electrochemical cell which is not entirely dry, but has no loose liquid.

• A current may be generated by electromagnetic induction, when there is relative motion of a conductor and a magnetic field: it does not matter which one moves.

• A dynamo produces direct current. While many devices need DC to operate, it is generally easier to transmit electrical power as alternating current.

• Electrical currents may be alternating current or direct current. In alternating current, the peak voltage is greater than the average voltage.

• Alternating currents are easier to change the voltage of, using a transformer to step the voltage up or down. This is why domestic supplies are all AC.

• Metals make good electrical conductors, non-metals can make good insulators: this related to the availability of free electrons in their structures.

• Electric circuits need to be closed before a current will flow in the circuit: a switch can open and shut a circuit, and switches can be of many sorts.

• Electrical systems are often protected by fuses and circuit breakers, which are designed to stop overload that might burn out expensive wiring and cause fires.

• Many electrical systems are fitted with sensitive detectors that cut the current in the event of any 'leakage to earth', which usually indicates a fault.

• A galvanometer can be used to detect a very small electrical current, using a coil to produce a small magnetic field that interacts with a permanent magnet.

• Electrical currents can be measured: the unit of current is the ampere, and current is measured with a modified galvanometer called an ammeter.

• Potential difference can be measured: the unit of potential is the volt, and voltage is measured with a modified galvanometer called a voltmeter.

• Wattmeters/Joule meters measure the energy transferred, and are more useful when it comes to charging consumers for the electricity they use.

• In 1911, Heike Kammerlingh Onnes discovered superconductivity in extremely cold conductors, having mastered the art of attaining low temperatures.

• In 1957, John Bardeen, Leon Cooper and Robert Schrieffer develop the BCS theory of superconductivity to explain why some substances are superconducting.

• Until superconductors are found that operate at room temperature (or above the boiling point of nitrogen), superconductivity will be of little practical use.

• If there is a magnetic field near a conductor in which a current is flowing, there will be a force on the conductor. This is the basis of the electric motor.

This file is http://members.ozemail.com.au/~macinnis/scifun/, first created on February 18, 2009. Last recorded revision (well I get lazy and forget sometimes!) was on February 18, 2009.

©The author of this work is Peter Macinnis, who asserts his sole right to the product as it is packaged here, recognising that many of the ideas are common. You are free to use this as a model to do your own version. Copies of this whole file or site may be made and stored or printed for personal or educational use. You can contact me at macinnis@ozemail.com.au, but only if you add my first name to the front of that email address -- this is a low-tech way of making it harder to harvest the e-mail address I actually read.
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