Encyclopedia
- For songs called Electricity, see Electricity .
Electricity is a general term for the variety of phenomena resulting from the presence and flow of electric charge. Together with
magnetism, it constitutes the fundamental interaction known as electromagnetism. It includes many well-known
physical phenomena such as
lightning,
electric fields and electric currents, and is put to use in
industrial applications such as
electronics and
electric power.
Concepts in electricity
In casual usage, the term
electricity is applied to several related concepts that are better identified by more precise terms:
- Electric potential - the potential energy per unit charge associated with a static electric field.
- Electric current - a movement or flow of electrically charged particles.
- Electric field - an effect produced by an electric charge that exerts a force on charged objects in its vicinity.
- Electrical energy - the energy made available by the flow of electric charge through an electrical conductor.
- Electric power - the rate at which electric energy is converted to or from another energy form, such as light, heat, or mechanical energy.
- Electric charge - a fundamental conserved property of some subatomic particles, which determines their electromagnetic interactions. Electrically charged matter is influenced by, and produces, electromagnetic fields.
History of discovery
The
ancient Greeks and
Parthians knew of static electricity from rubbing objects against fur.
Though scientific exploration into the phenomenon began during the European
Renaissance, electricity was known only as a curiosity and a party trick until more substantial discoveries were made in the late
18th to mid
19th century.
Though
Benjamin Franklin's famous "invention" of electricity by flying a kite in a thunderstorm turned out to be more fiction than fact, his theories on the relationship between lightning and static electricity sparked the interest of later scientists whose work provided the basis for modern electrical technology. Most notably these include
Michael Faraday ,
Luigi Galvani ,
Alessandro Volta ,
André-Marie Ampère , and
Georg Simon Ohm .
The late 19th and early 20th century produced such giants of electrical engineering as
Nikola Tesla,
Samuel Morse,
Antonio Meucci,
Thomas Edison,
George Westinghouse,
Werner von Siemens,
Charles Steinmetz, and
Alexander Graham Bell.
Concepts in detail
Electric charge
Electric charge is a property of certain
subatomic particles which interacts with electromagnetic fields and causes attractive and repulsive forces between them.
Electric charge gives rise to one of the four fundamental forces of nature, and is a conserved property of matter that can be quantified. In this sense, the phrase "quantity of electricity" is used interchangeably with the phrases "charge of electricity" and "quantity of charge." There are two types of charge: we call one kind of charge positive and the other negative. Through experimentation, we find that like-charged objects repel and opposite-charged objects attract one another. The magnitude of the force of attraction or repulsion is given by
Coulomb's law.
Electric field
The concept of electric field was introduced by
Michael Faraday. The electrical field force acts between two charges, in the same way that the
gravitational field force acts between two
masses. However, the electric field is a little bit different. Gravitational force depends on the masses of two bodies, whereas electric force depends on the electric charges of two bodies. While gravity can only pull two masses together, the electric force can be an attractive
or repulsive force. If both charges are of same sign , there will be a repulsive force between the two. If the charges are opposite, there will be an attractive force between the two bodies. The magnitude of the force varies inversely with the square of the distance between the two bodies, and is also proportional to the product of the unsigned magnitudes of the two charges.
Electric potential
The electric potential difference between two points is defined as the work done per unit charge in moving a positive point charge slowly between two points. If one of the points is taken to be a reference point with zero potential, then the electric potential at any point can be defined in terms of the work done per unit charge in moving a positive point charge from that reference point to the point at which the potential is to be determined. For isolated charges, the reference point is usually taken to be
infinity. The potential is measured in
volts. The electric potential is analogous to temperature: there is a different temperature at every point in space, and the temperature gradient indicates the direction and magnitude of the driving force behind heat flow. Similarly, there is an electric potential at every point in space, and its
gradient indicates the direction and magnitude of the driving force behind charge movement.
electricity
Bold textElectric current
An electric current is a flow of electric charge, and its intensity is measured in
amperes. Examples of electric currents include metallic conduction, where
electrons flow through a conductor such as a metal
wire, and
electrolysis, where ions flow through liquids. The particles themselves often move quite slowly, while the
electric field that drives them propagates at close to the
speed of light. See
electrical conduction for more information.
Devices that use charge flow principles in materials are called
electronic devices.
A
direct current is a unidirectional flow, while an
alternating current reverses direction repeatedly. The time average of an alternating current is zero, but its energy capability is not zero.
Ohm's Law is an important relationship describing the behaviour of electric currents, relating them to
voltage.
For historical reasons, electric
current is said to flow from the most positive part of a circuit to the most negative part. The electric current thus defined is called
conventional current. It is now known that, depending on the conditions, an electric current can consist of a flow of charged particles in either direction, or even in both directions at once. The positive-to-negative convention is widely used to simplify this situation. If another definition is used - for example, "electron current" - it should be explicitly stated.
Electrical energy
Electrical energy is energy stored in an
electric field or transported by an electric current. Energy is defined as the ability to do work, and electrical energy is simply one of the many types of energy. Examples of electrical energy include:
- the energy that is constantly stored in the Earth's atmosphere, and is partly released during a thunderstorm in the form of lightning
- the energy that is stored in the coils of an electrical generator in a power station, and is then transmitted by wires to the consumer; the consumer then pays for each unit of energy received
- the energy that is stored in a capacitor, and can be released to drive a current through an electrical circuit
Electric power
Electric power is the rate at which electrical energy is produced or consumed, and is measured in watts .
A
fossil-fuel or
nuclear power station converts heat to electrical energy, and the faster the station burns fuel, assuming constant efficiency of conversion, the higher its power output. The output of a power station is usually specified in megawatts . The electrical energy is then sent over
transmission lines to reach the consumers.
Every consumer uses appliances that convert the electrical energy to other forms of energy, such as
heat ,
light , or motion, i.e. kinetic energy . Like the power station, each appliance is also rated in watts, depending on the rate at which it converts electrical energy into another form. The power station must produce electrical energy at the same rate as all the connected appliances consume it.
In electrical engineering, the concepts of
apparent power and
reactive power are also used. Apparent power is the product of RMS voltage and RMS current, and is measured in volt-amperes .
Reactive power is measured in volt-amperes-reactive .
Non-nuclear electric power is categorized as either green or brown electricity.
Green power is a cleaner alternative energy source in comparison to traditional sources, and is derived from renewable energy resources that do not produce any nuclear waste; examples include energy produced from wind, water, solar, thermal, hydro, combustible renewables and waste.
Electricity from coal, oil, and natural gas is known as traditional power or "brown" electricity.
SI electricity units
See also
Devices
Engineering
Safety
Electrical phenomena in nature
- Matter: — since atoms and molecules are held together by electric forces.
- Lightning: electrical discharges in the atmosphere.
- The Earth's magnetic field — created by electric currents circulating in the planet's core.
- Sometimes due to solar flares, a phenomenon known as a power surge can be created.
- Piezoelectricity: the ability of certain crystals to generate a voltage in response to applied mechanical stress.
- Triboelectricity: electric charge taken on by contact or friction between two different materials.
- Bioelectromagnetism: electrical phenomena within living organisms.
- Bioelectricity — Many animals are sensitive to electric fields, some more than others . Most also generate their own electric fields.
External links
-
-
-
-
-
- , Created and Collected by Robert A. Morse
-
-
-
-
Notes
