# HIGHLIGHTS

1. 8.       Permeability is the ratio of flux density to magnetic field strength.
2. 9.       Hysteresis is defined as the lagging of magnetisation or induction flux density (B) behind the magnetizing force (H).
3. 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.
4. 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”.

1. 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 direction that magnetic field which is caused by that current will oppose the change that produced the current”.
2. 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.

1. 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.
2. 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.
3. 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.