Correct Answer - Option 3 : reluctance

__Concept:__

Reluctance opposes the **passage of magnetic flux lines**. Reluctance is analogous to resistance.

We can define the reluctance as,

\(\Re = \frac{{mmf}}{{flux}}\)

We know that, \(H = \frac{{NI}}{l}\)

Where H is field strength

N is the number of turns in a coil

l is mean length of flux in a magnetic circuit

I is current through the coil

The flux in a magnetic circuit is given by

\(\phi = BA\)

\(= \mu HA\)

\(= \mu \left( {\frac{{NI}}{l}} \right)A\)

\(\Rightarrow \phi = \frac{{NI}}{{\frac{1}{\mu }\frac{l}{A}}} = \frac{{mmf}}{{reluctance}} = \frac{{mmf}}{\Re}\)

Now, we can define reluctance as \(\Re = \frac{l}{{\mu A}} = \frac{l}{{{\mu _0}{\mu _r}}A}\)

**Important Points:**

Impedance(Z) is given by Z = R + jX

Where,

Z = Impedance in Ohm

R = Resistance in Ohm

X = Reactance in Ohm

Then Admittance(Y) can be expressed as

Y= a + jb

Where,

Y = Admittance in siemens

a = Conductance in siemens \(= \frac{R}{{{R^2} + {X^2}}}\)

b = Susceptance in siemens \(= \frac{{ - X}}{{{R^2} + {X^2}}}\)