Electromagnetism is the physics of the electromagnetic field, a field that exerts a force on particles with the property of electric charge and is reciprocally affected by the presence and motion of such particles.
A changing magnetic field produces an electric field (this is the phenomenon of electromagnetic induction, the basis of operation for electrical generators, induction motors, and transformers). Similarly, a changing electric field generates a magnetic field.
The magnetic field is produced by the motion of electric charges, i.e., electric current. The magnetic field causes the magnetic force associated with magnets.
The theoretical implications of electromagnetism led to the development of special relativity by Albert Einstein in 1905; and from this it was shown that magnetic fields and electric fields are convertible with relative motion as a four vector and this led to their unification as electromagnetism
Wednesday, September 30, 2009
Electric potential
At a point in space, the electric potential (also called the "electrostatic potential") is potential energy divided by charge that is associated with a static (time-invariant) electric field. It is a scalar quantity, typically measured in volts.
There is also a generalized electric scalar potential that is used in electrodynamics when time-varying electromagnetic fields are present. This generalized electric potential cannot be simply interpreted as the ratio of potential energy to charge, however.
There is also a generalized electric scalar potential that is used in electrodynamics when time-varying electromagnetic fields are present. This generalized electric potential cannot be simply interpreted as the ratio of potential energy to charge, however.
Tuesday, September 29, 2009
electric current
Electric current can mean, depending on the context, a flow of electric charge (a phenomenon) or the rate of flow of electric charge (a quantity).[1] The electric charge that flows is carried by, for example, mobile electrons in a conductor, ions in an electrolyte or both in a plasma.[2]
The SI unit for rate of flow of electric charge is the ampere. Electric current is measured using an ammeter
The SI unit for rate of flow of electric charge is the ampere. Electric current is measured using an ammeter
electric charge
Electric charge is a fundamental conserved property of some subatomic particles, which determines their electromagnetic interaction. Electrically charged matter is influenced by, and produces, electromagnetic fields. The interaction between a moving charge and an electromagnetic field is the source of the electromagnetic force, which is one of the four fundamental forces.
The electric charge on a body may be positive or negative. Two positively charged bodies experience a mutual repulsive force, as do two negatively charged bodies. A positively charged body and a negatively charged body experience an attractive force. The study of how charged bodies interact is classical electrodynamics, which is accurate insofar as quantum effects can be ignored.
Twentieth-century experiments demonstrated that electric charge is quantized: the charge of any system, body, or particle (except quarks) is an integer multiple of the elementary charge, e, approximately equal to 1.602×10−19 coulombs. The proton has a charge of e, and the electron has a charge of −e. The study of charged particles, and how their interactions are mediated by photons, is quantum electrodynamics
The electric charge on a body may be positive or negative. Two positively charged bodies experience a mutual repulsive force, as do two negatively charged bodies. A positively charged body and a negatively charged body experience an attractive force. The study of how charged bodies interact is classical electrodynamics, which is accurate insofar as quantum effects can be ignored.
Twentieth-century experiments demonstrated that electric charge is quantized: the charge of any system, body, or particle (except quarks) is an integer multiple of the elementary charge, e, approximately equal to 1.602×10−19 coulombs. The proton has a charge of e, and the electron has a charge of −e. The study of charged particles, and how their interactions are mediated by photons, is quantum electrodynamics
Saturday, September 26, 2009
history of electricity
1.Long before any knowledge of electricity existed people were aware of shocks from electric fish. Ancient Egyptian texts dating from 2750 BC referred to these fish as the "Thunderer of the Nile", and described them as the "protectors" of all other fish. They were again reported millennia later by ancient Greek, Roman and Arabic naturalists and physicians.
2.Several ancient writers, such as Pliny the Elder and Scribonius Largus, attested to the numbing effect of electric shocks delivered by catfish and torpedo rays, and knew that such shocks could travel along conducting objects
3.Patients suffering from ailments such as gout or headache were directed to touch electric fish in the hope that the powerful jolt might cure them
4. Possibly the earliest and nearest approach to the discovery of the identity of lightning, and electricity from any other source, is to be attributed to the Arabs, who before the 15th century had the Arabic word for lightning (raad) applied to the electric ray
5.That certain objects such as rods of amber could be rubbed with cat's fur and attract light objects like feathers was known to ancient cultures around the Mediterranean. Thales of Miletos made a series of observations on static electricity around 600 BC, from which he believed that friction rendered amber magnetic, in contrast to minerals such as magnetite, which needed no rubbing
6. Thales was incorrect in believing the attraction was due to a magnetic effect, but later science would prove a link between magnetism and electricity. According to a controversial theory, the Parthians may have had knowledge of electroplating, based on the 1936 discovery of the Baghdad Battery, which resembles a galvanic cell, though it is uncertain whether the artifact was electrical in nature
7.Electricity would remain little more than an intellectual curiosity for millennia until 1600, when the English physician William Gilbert made a careful study of electricity and magnetism, distinguishing the lodestone effect from static electricity produced by rubbing amber.
8. He coined the New Latin word electricus ("of amber" or "like amber", from ήλεκτρον [elektron], the Greek word for "amber") to refer to the property of attracting small objects after being rubbed
9.This association gave rise to the English words "electric" and "electricity", which made their first appearance in print in Thomas Browne's Pseudodoxia Epidemica of 1646
10Further work was conducted by Otto von Guericke, Robert Boyle, Stephen Gray and C. F. du Fay. In the 18th century, Benjamin Franklin conducted extensive research in electricity, selling his possessions to fund his work. In June 1752 he is reputed to have attached a metal key to the bottom of a dampened kite string and flown the kite in a storm-threatened sky
11. A succession of sparks jumping from the key to the back of the hand showed that lightning was indeed electrical in nature
12.In 1791, Luigi Galvani published his discovery of bioelectricity, demonstrating that electricity was the medium by which nerve cells passed signals to the muscles
13. Alessandro Volta's battery, or voltaic pile, of 1800, made from alternating layers of zinc and copper, provided scientists with a more reliable source of electrical energy than the electrostatic machines previously used
14.The recognition of electromagnetism, the unity of electric and magnetic phenomena, is due to Hans Christian Ørsted and André-Marie Ampère in 1819-1820; Michael Faraday invented the electric motor in 1821, and Georg Ohm mathematically analysed the electrical circuit in 1827
15.While it had been the early 19th century that had seen rapid progress in electrical science, the late 19th century would see the greatest progress in electrical engineering. Through such people as Nikola Tesla, Thomas Edison, Ottó Bláthy, Sir Charles Parsons, George Westinghouse, Ernst Werner von Siemens, Alexander Graham Bell and Lord Kelvin, electricity was turned from a scientific curiosity into an essential tool for modern life, becoming a driving force for the Second Industrial Revolution
2.Several ancient writers, such as Pliny the Elder and Scribonius Largus, attested to the numbing effect of electric shocks delivered by catfish and torpedo rays, and knew that such shocks could travel along conducting objects
3.Patients suffering from ailments such as gout or headache were directed to touch electric fish in the hope that the powerful jolt might cure them
4. Possibly the earliest and nearest approach to the discovery of the identity of lightning, and electricity from any other source, is to be attributed to the Arabs, who before the 15th century had the Arabic word for lightning (raad) applied to the electric ray
5.That certain objects such as rods of amber could be rubbed with cat's fur and attract light objects like feathers was known to ancient cultures around the Mediterranean. Thales of Miletos made a series of observations on static electricity around 600 BC, from which he believed that friction rendered amber magnetic, in contrast to minerals such as magnetite, which needed no rubbing
6. Thales was incorrect in believing the attraction was due to a magnetic effect, but later science would prove a link between magnetism and electricity. According to a controversial theory, the Parthians may have had knowledge of electroplating, based on the 1936 discovery of the Baghdad Battery, which resembles a galvanic cell, though it is uncertain whether the artifact was electrical in nature
7.Electricity would remain little more than an intellectual curiosity for millennia until 1600, when the English physician William Gilbert made a careful study of electricity and magnetism, distinguishing the lodestone effect from static electricity produced by rubbing amber.
8. He coined the New Latin word electricus ("of amber" or "like amber", from ήλεκτρον [elektron], the Greek word for "amber") to refer to the property of attracting small objects after being rubbed
9.This association gave rise to the English words "electric" and "electricity", which made their first appearance in print in Thomas Browne's Pseudodoxia Epidemica of 1646
10Further work was conducted by Otto von Guericke, Robert Boyle, Stephen Gray and C. F. du Fay. In the 18th century, Benjamin Franklin conducted extensive research in electricity, selling his possessions to fund his work. In June 1752 he is reputed to have attached a metal key to the bottom of a dampened kite string and flown the kite in a storm-threatened sky
11. A succession of sparks jumping from the key to the back of the hand showed that lightning was indeed electrical in nature
12.In 1791, Luigi Galvani published his discovery of bioelectricity, demonstrating that electricity was the medium by which nerve cells passed signals to the muscles
13. Alessandro Volta's battery, or voltaic pile, of 1800, made from alternating layers of zinc and copper, provided scientists with a more reliable source of electrical energy than the electrostatic machines previously used
14.The recognition of electromagnetism, the unity of electric and magnetic phenomena, is due to Hans Christian Ørsted and André-Marie Ampère in 1819-1820; Michael Faraday invented the electric motor in 1821, and Georg Ohm mathematically analysed the electrical circuit in 1827
15.While it had been the early 19th century that had seen rapid progress in electrical science, the late 19th century would see the greatest progress in electrical engineering. Through such people as Nikola Tesla, Thomas Edison, Ottó Bláthy, Sir Charles Parsons, George Westinghouse, Ernst Werner von Siemens, Alexander Graham Bell and Lord Kelvin, electricity was turned from a scientific curiosity into an essential tool for modern life, becoming a driving force for the Second Industrial Revolution
electricity
Electricity (from the New Latin ēlectricus, "amber-like"[a]) is a general term that encompasses a variety of phenomena resulting from the presence and flow of electric charge. These include many easily recognizable phenomena, such as lightning and static electricity, but in addition, less familiar concepts, such as the electromagnetic field and electromagnetic induction
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