Terms used In Electricity
Conductor is a material through which electric current
Electric charge is a basic feature of certain particles
of matter that causes them to attract or repel other charged
Electric circuit is the path that an electric current follows.
Electric current is the flow of electric charges.
Electric field is the influence a charged body has on the
space around it that causes other charged bodies in that
space to experience electric forces.
Electrode is a piece of metal or other conductor through
which current enters or leaves an electric device.
Electromagnetism is a basic force in the universe that involves
both electricity and magnetism.
Electron is a subatomic particle with a negative electric
Insulator is a material that opposes the flow of electric
Ion is an atom or group of atoms that has either gained
or lost electrons, and so has an electric charge.
Kilowatt-hour is the amount of electric energy a 1,000-watt
device uses in one hour.
Neutron is a subatomic particle that has no electric charge.
Ohm is the unit used to measure a material's resistance
to the flow of electric current.
Proton is a subatomic particle with a positive electric
Resistance is a material's opposition to the flow of electric
Static electricity is electric charge that is not moving.
Voltage is a type of "pressure" that drives electric
charges through a circuit.
Watt is the unit used to measure the rate of energy consumption,
including electric energy.
Electric current is the movement or flow of electric charges.
A charge can be either positive or negative. The protons
that make up part of the nucleus of every atom have a positive
electric charge. The electrons that surround the nucleus
have a negative charge. An electric current can consist
of positive, negative, or both types of charges.
The American statesman and scientist Benjamin Franklin
originated the idea that electric current flows from positive
to negative. But other scientists later proved that electric
current actually flows in the opposite direction--from negative
Franklin's idea also fails to describe the way electric
current flows through metals. Each atom of a metal wire
has at least one electron that is not held so closely by
the nucleus as the others are. Such loosely held electrons
can move freely through the metal. But the nucleus cannot
move through the wire. Thus, current flowing through a metal
wire consists of free electrons.
Conductors and insulators. Electric current flows most
easily through substances called conductors. The number
of free electrons in a substance determines how well it
conducts current. Such metals as aluminium, copper, silver,
and gold are good conductors because they have at least
one free electron per atom. Some metals, such as lead and
tin, are poorer conductors than other metals because they
have less than one free electron per atom. Poor conductors
resist the flow of electric current more than good conductors
do. Resistance changes electric energy into heat. Engineers
use units called ohms to measure resistance (see OHM).
Substances with no free electrons, such as glass, mica,
and rubber, do not normally conduct electric current. They
are called insulators. Some substances, including germanium
and silicon, are neither good conductors nor insulators.
They are called semiconductors (see SEMICONDUCTOR).
To produce an electric current, some type of nonelectric
energy must be converted into an electromotive force (emf).
For example, a battery creates an emf by changing chemical
energy into electrical potential energy. Thus, a battery
has a potential difference (difference in potential energy)
between its ends that causes electrons to flow in a conductor.
Emf is measured in units called volts. An emf of one volt,
when connected to a conductor with a resistance of one ohm,
causes 6,241,500,000,000,000,000 electrons to flow past
a point in the conductor in one second. This amount of electric
current is called one ampere. See VOLT; AMPERE.
Direct and alternating current. An electric current is
either direct or alternating. Direct current (DC) always
flows in the same direction. It is produced by batteries
and DC generators. Alternating current (AC) regularly reverses
its direction of flow. It is produced by AC generators.
Nearly all homes and other buildings use AC.
Each time AC completes two changes of direction, it goes
through one cycle. The number of cycles per second is called
the frequency of the AC. Frequency is measured in units
called hertz. Power is generated at 50 hertz in some countries
and 60 hertz in others.
Direct current operates car electric systems, locomotives,
and some types of motors used in industry. Radios, television
sets, and other electronic devices use AC, but they also
need DC to operate their internal circuits. Devices called
rectifiers easily change AC into DC. DC is also necessary
in order to charge storage batteries.
Alternating current has several advantages over DC. Its
major advantage is that power stations can transmit it easily
and efficiently. Electric current loses the least amount
of energy when travelling at high voltages. But these high
voltages are not safe to use in homes. Devices called transformers
can easily increase or decrease AC voltage.
A conductor can carry more than one alternating current
at a time. A current consisting of two more individual alternating
currents is known as a polyphase current. One common kind
of polyphase current is three-phase current, which consists
of three individual alternating currents.