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There are four basic laws which describe the behaviour of electric and magnetic fields, the relation between them and their generation by charges and currents.
There are four basic laws which describe the behaviour of electric and magnetic fields, the relation between them and their generation by charges and currents.
These laws are as follows.
These laws are as follows.
(1) Gauss' law for electrostatics which is essentially the Coulomb’s law describes the relationship between static electric charges and the electric field produced by them.
(1) Gauss' law for electrostatics which is essentially the Coulomb’s law describes the relationship between static electric charges and the electric field produced by them.
(2) Gauss' law for magnetism, which is similar to the Gauss' law for electrostatics as mentioned above states that "magnetic monopoles which are thought to be magnetic charges equivalent to the electric charges, do not exist". Magnetic poles always occur in pairs.
(2) Gauss' law for magnetism, which is similar to the Gauss' law for electrostatics as mentioned above states that "magnetic monopoles which are thought to be magnetic charges equivalent to the electric charges, do not exist". Magnetic poles always occur in pairs.
(3) Faraday’s law which gives the relation between electromotive force (emf) induced in a circuit when the magnetic flux linked with the circuit changes.
(3) Faraday’s law which gives the relation between electromotive force (emf) induced in a circuit when the magnetic flux linked with the circuit changes.
(4) Ampere’s law gives the relation between the induced magnetic field associated with a loop and the current flowing through the loop.
(4) Ampere’s law gives the relation between the induced magnetic field associated with a loop and the current flowing through the loop.
Maxwell (1831-1879) noticed a major flaw in the Ampere’s law for time dependant fields.
Maxwell (1831-1879) noticed a major flaw in the Ampere’s law for time dependant fields.
He noticed that the magnetic field can be generated not only by electric current but also by changing electric field.
He noticed that the magnetic field can be generated not only by electric current but also by changing electric field.
Therefore in the year 1861, he added one more term to the equation describing this law. This term is called the displacement current.
Therefore in the year 1861, he added one more term to the equation describing this law. This term is called the displacement current.
This term is extremely important and the EM waves which are an outcome of these equations would not have been possible in absence of this term.
This term is extremely important and the EM waves which are an outcome of these equations would not have been possible in absence of this term.
As a result, the set of four equations describing the above four laws is called Maxwell’s equations.
As a result, the set of four equations describing the above four laws is called Maxwell’s equations.
In 1888, H. Hertz (1857-1894) succeeded in producing and detecting the existence of EM waves.
In 1888, H. Hertz (1857-1894) succeeded in producing and detecting the existence of EM waves.
He also demonstrated their properties namely reflection, refraction and interference. In 1895, an Indian physicist Sir Jagdish Chandra Bose (1858-1937) produced EM waves ranging in wavelengths from 5 mm to 25 nm.
He also demonstrated their properties namely reflection, refraction and interference. In 1895, an Indian physicist Sir Jagdish Chandra Bose (1858-1937) produced EM waves ranging in wavelengths from 5 mm to 25 nm.
His work, however, remained confined to laboratory only.
His work, however, remained confined to laboratory only.
In 1896, an Italian physicist G. Marconi (1874-1937) became pioneer in establishing wireless communication.
In 1896, an Italian physicist G. Marconi (1874-1937) became pioneer in establishing wireless communication.
He was awarded the Nobel prize in physics in 1909 for his work in developing wireless telegraphy, telephony and broadcasting.
He was awarded the Nobel prize in physics in 1909 for his work in developing wireless telegraphy, telephony and broadcasting.
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