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49. (a)
4. Self-induction We have learnt that when a current passes through a coil, some magnetic field is created so that the coil itself behaves like a magnet. The magnetic flux produced by the current in the coil is linked with the coil itself and when the current in the coil changes, this flux linked with the coil also changes. Under such circumstances also, there would be an emf induced in the coil which is called the 'self-induction'. The value of mutual inductance of a system of two coils depends upon their shapes, sizes, their number of turns, distance between them, their mutual inclination angle and the material on which they are wound. Text-book of Physics (Part - II), op.cit, p. 94 "Electromagnetic waves discovered relatively recently-only in the later part of the 19th century. It was the result of the synthesis of various facts and laws pertaining to electricity and magnetism, like Gauss' law, Ampere's law, Faraday's law, the closed nature of magnetic field lines etc. by a British scientist James Clerk Maxwell in form of Maxwell's equations. These are the differential equations which interconnect electric and magnetic field parameters through differential equations. Examination of these equations in terms of symmetry between electric and magnetic phenomena also lead to the famous contribution due to Maxwell of the term called the displacement current a term which provided the missing aspect to complete the symmetry.” Satish K. Gupta, op.cit., p. 731"These equations govern the behaviour of electric and magnetic fields. Maxwell showed that these equations predict the existence of electromagnetic waves, which propagate through the space in the form of varying electric and magnetic fields. He also showed that these waves are transverse in nature and travel with the speed of light. 1. Gauss's law in electrostatics. It states that the total electric flux through any closed surface- is always equal to lle, times the net charge enclosed by the surface. 2. Gauss's law in magnetism. It states the net magnetic flux crossing any closed surface is always zero. A direct consequence of Gauss's magnetism is that an isolated magnetic monopole does not exist. 3. Faraday's law of electromagnetic induction. It states that
(b)
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