**8.****Permeability**is the ratio of flux density to magnetic field strength.**9.**Hysteresis is defined as the lagging of magnetisation or induction flux density*(B)*behind the magnetizing force (H).**10.***“The phenomenon**whereby an e.m.f and hence current is induced in any conductor which*is*cut across or**is cut by a magnetic flux**is known as***electromagnetic induction.****11.****Faraday’s first law.**It states that:*“Whenever the magnetic flux linked with*a*circuit changes, an*e.m.f. is always*induced**in it”.*

*Or*

*“Whenever a conductor cuts magnetic **flux, an e.m.f is induced in that conductor”. *

**12.****Lenz’s law***It states that : “In all cases of electromagnetic induction, an induced voltage will cause**a**current to flow in a closed circuit in such a d**irection that magnetic field which is caused by that current**will oppose the change that produced the current”.***13.**The e.m.f. induced by variation of flux is termed as “statically induced e.m.f.” It is further subdidvided as:

(i) Self-induced e.m.f. ;

(j) Mutually induced e.m.f.

**14.***The property of the coil due to which it opposes any increase or decrease of the current or flux through it, is known as*self-inductance.**15.***Mutual inductance*is the ability of one coil (or circuit) to produce e.m.f. in a near by coil by induction when the current in the first coil changes.**16.**Co-efficient of couplingis defined as the ratio of mutual inductance between the coils and the square root of product of self-inductance of each coil.

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