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Theory of Electricity
There is an equal number of electrons and protons in an atom. Hence, atom is in general electrically neutral. As the protons in the central nucleus are positive in charge and electrons orbiting the nucleus, are negative in charge, there will be an attraction force acts between the electrons and protons. In an atom various electrons arrange themselves in different orbiting shells situated at different distances from the nucleus.
The force is more active to the electrons nearer to the nucleus, than to the electrons situated at outer shell of the atom. One or more of these loosely bonded electrons may be detached from the atom. The atoms with lack of electrons are called ions. Due to lack of electrons, compared to number of protons, the said ion becomes positively charged. Hence, this ion is referred as positive ion and because of positive electrical charge; this ion can attract other electrons from outside. The electron, which was previously detached from any other atom, may occupy the outer most shell of this ion and hence this ion again becomes neutral atom. The electrons which move from atom to atom in random manner are called free elections. When a voltage is applied across a conductor, due to presence of electric field, the free electrons start drifting to a particular direction according the direction of voltage and electric field. This phenomenon causes electric current in the conductor. The movement of electrons, means movement of negative charge and rate of this charge transfer with respect to time is known as electric current.
The amount of negative electric charge in an electron is 1.602 X 10-19 Coulomb. Hence, one coulomb negative electric charge consists of 1/1.602 X 10 -19 = 6.24 X 10 18number of electrons. Hence, during drift of electron to a particular direction, if 6.24 X 10 18 number of electrons cross a specific cross-section of the conductor, in one second, the electric current is said to be one ampere. Since, we have already seen the unit of electric current, ampere is coulomb/second.
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