ELECTRICITY

Michael Faraday

The concept of electric fields 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 (e.g. both positive), 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.

[edit] Electric potential

Main article: Electric potential

The electric potential difference between two points is defined as the work done per unit charge (against electrical forces) 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. (1 volt = 1 joule/coulomb) 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

[edit] Electric current

Main article: Current (electricity)

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 or conductors such as a metal wire, and electrolysis, where ions (charged atoms) 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 (DC) is a unidirectional flow, while an alternating current (AC) reverses direction repeatedly. The time average of an alternating current is zero, but its energy capability (RMS value) 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.

[edit] Electrical energy

Main article: 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

[edit] Electric power

Main article: Electric power

Electric power is the rate at which electrical energy is produced or consumed, and is measured in watts (symbol is: W).

A nuclear power station.

A fossil-fuel, solar-thermal, nuclear or biomass power station converts heat to electrical energy, and the faster the station burns fuel, assuming positively-sloped efficiency of conversion, the higher its power output. The output of a power station is usually specified in megawatts (millions of watts). 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 (in electric arc furnaces and electric heaters), light (in light bulbs and fluorescent lamps), or motion, i.e. kinetic energy (in electric motors). 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 (VA). Reactive power is measured in volt-amperes-reactive (VAr).

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.

[edit] SI electricity units

SI electromagnetism units
Symbol [citation needed]	Name of Quantity	Derived Units	Unit	Base Units
I	Magnitude of current	ampere (SI base unit)	A	A = W/V = C/s
q	Electric charge, Quantity of electricity	coulomb	C	A·s
U	Potential difference or Electromotive force	volt	V	J/C = kg·m2·s−3·A−1
R, Z, X	Resistance, Impedance, Reactance	ohm	Ω	V/A = kg·m2·s−3·A−2
ρ	Resistivity	ohm metre	Ω·m	kg·m3·s−3·A−2
P	Power, Electrical	watt	W	V·A = kg·m2·s−3
C	Capacitance	farad	F	C/V = kg−1·m−2·A2·s4
	Elastance	reciprocal farad	F−1	V/C = kg·m2·A−2·s−4
ε	Permittivity	farad per metre	F/m	kg−1·m−3·A2·s4
χe	Electric susceptibility	(dimensionless)	-	-
G, Y, B	Conductance, Admittance, Susceptance	siemens	S	Ω−1 = kg−1·m−2·s3·A2
σ	Conductivity	siemens per metre	S/m	kg−1·m−3·s3·A2
H	Magnetic field, magnetic field intensity	ampere per metre	A/m	A·m−1
Φm	Magnetic flux	weber	Wb	V·s = kg·m2·s−2·A−1
B	Magnetic flux density, magnetic induction, magnetic field strength	tesla	T	Wb/m2 = kg·s−2·A−1 = N·A−1·m−1
	Reluctance	ampere-turn per weber	A/Wb	kg−1·m−2·s2·A2
L	Inductance	henry	H	Wb/A = V·s/A = kg·m2·s−2·A−2
μ	Permeability	henry per metre	H/m	kg·m·s−2·A−2
χm	Magnetic susceptibility	(dimensionless)	-	-

[edit] See also

• Electrical phenomena
• Electricity generation
• Electromagnetism
• Electrostatics

[edit] Devices

• Battery
• Conductor
• Insulator
• Light fixture

[edit] Engineering

• Green electricity
• Electrical engineering
• Electrical wiring
• MicroCHP

[edit] Safety

• Electric shock and injuries
• High-voltage hazards

[edit] 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 (e.g., sharks) more than others (e.g., people). Most also generate their own electric fields.
    • Gymnotiformes, such as the electric eel, deliberately generate strong fields to detect or stun their prey.
    • Neurons in the nervous system transmit information by electrical impulses known as action potentials.

[edit] External links

• Merriam-Webster: Electricity
• Tyndall: Faraday as Discovery: Identity of Electricities
• US Energy Department Statistics
• Read Congressional Research Service (CRS) Reports regarding Electricity
• How to save on your electricity bills
• Electricity around the world
• A Comprehensive Collection of Franklin’s Electrical Works: The Electrical Writings of Benjamin Franklin, Created and Collected by Robert A. Morse (2004)
• Understanding Electricity and some Electronics in 10 minutes(Steve Rose, Maui)
• Electricity Misconceptions
• Electricity and Magnetism
• Electricity and electrical installation guide

[edit] Notes