PEE-6

What are the difference between magnetic circuit and electric circuit, compare ?
Ans :-
MAGNETIC CIRCUIT                                           ELECTRIC CIRCUIT
1/ The closed path followed by             1/ The closed path for electric current is
 magnetic flux is called magnetic              called an electric circuit.
circuit.
2/Flux,Ø = mmf/reluctance                    2/ Current, I =EMF/RESISTANCE
3/ mmf ( ampere-turns )                         3/ emf ( volts )
4/ Reluctance, S = L/(aμ.μr)                  4/ Resistance, R = þ l/a
5/ Flux density, B = ∅/A Wb/m2            5/ Current density, J = I/a A/m2
6/ mmf drop = ØS                                   6/ Voltage drop = IR
7/Magnetic intensity, H= NI/l AT/M      7/ Electric intensity, E = V/d volt/m
8/ Permeability = 1/reluctivity                8/ Conductivity = 1/resistivity


What is leakage flux ?
Ans :-
        The magnetic flux that does not flow the desired path in a
magnetic is called a leakage flux.
Let
Øi = Total magnetic flux
Øg = Useful magnetic flux across the air gap
So…………
Leakage Flux, ØLeakage = Øi - Øg


What is Leakage coefficient ?
Ans :-
      Leakage coefficient is the ratio of total flux produced ( That
is, flux in the iron ring ) to the useful flux across the air gap.
So, leakage coefficient, λ = (Total flux)/(useful flux) = Øi/Øg
What is electromagnetic induction ?
Ans :-
Whenever magnetic flux linked with the coil changes, an emf is
always induced in it. This induced emf is exit in the coil as long as
the changes in the magnetic flux continues. This phenomenon is known
as electromagnetic induction.

PEE-3

State and explain Faraday's law of electromagnetic induction.
Ans :-
Faraday gave the following two laws…………
FIRST LAW :- It states whenever the magnetic flux linked with a coil
or circuit changes, an e.m.f. is always induced in it. This e.m.f. is
exist in the circuit or coil as long as the changes in magnetic flux
continues.
OR
It states, whenever a conductor cuts magnetic flux, an e.m.f. is
induced in that conductor.
SECOND LAW :- It states, the magnitude of induced e.m.f. is directly
proportional to the rate of change of magnetic flux linked with the
circuit or coil.
We may also say that the magnitude of induced e.m.f. is equal to
the rate of change of flux-linkages.
EXPLANATION :-
Suppose a coil has N turns & flux through it changes from an
initial value of Ø₁   webers to the final value of Ø₂ webers in time t
seconds. Then, we have ( from Faraday's Law )………………
Initial flux linkages = NØ₁ and
Final flux linkages = NØ₂
So rate of change of magnetic flux
OR
induced e.m.f. ( e ) = ( NØ₂ - NØ₁ )/t wb/second or volt or
e = N( Ø₂ - Ø₁ )/t volt
Putting the above expression in its differential form, we have
e = d/dt ( NØ ) = N(d∅)/dt volt
Usually, a minus sign is given to the right-hand side expression
to signify the fact that the induced e.m.f. sets up current in such a
direction ( to oppose the change in flux ) that magnetic effect
produced by it opposes the very cause producing it.
So, e = - N(d∅)/dt volt .