For an explanation, see the main splats page
SPLATS about electrodynamics
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.
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