Written by Shailendra Kumar Bhartee. Posted in Engineering on 12 February 2010.
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Comparison between electrical circuit and magnetic circuit


From Amperes law we know that mmf (magneto motive force) around a closed path is equal to the current enclosed by the closed path.

That is integration of   H.dl = Ni    ………(1)

Where H = magnetic field intensity,

dl = small incremental length,

N = number of conductors and

i = current flowing in each conductors.

Now if H is constant then from equation (1)

Integration of H.dl = Ni

→  (H) integration of dl = Ni

→                          H . l  = Ni

therefore     H  = Ni/l       ………(2)

Now because flux ф = B.A = μH.A     (because B = μH)    …………(3)

Where B = magnetic flux density, H = magnetic field intensity, μ = permeability of medium and A = area.

Now from equation (2) and equation (3)

Ф = μNil /A

→ Ф = Ni / ( l / μA)   ………………(4)

Similarities between magnetic circuit and electric circuit


  • Magnetic circuit follows equation (4) that is Ni = (Ф) ( l / μA)   or m.m.f(magneto motive force) = (Flux) (reluctance).

Electric circuit follows ohm’s law that is E = I.R or e.m.f(electro motive force) = (current) (Resistance)

  • From above point m.m.f in magnetic circuit is like as e.m.f in electrical circuit.
  • Flux in magnetic circuit is similar as current in electrical circuit.
  • Reluctance in magnetic circuit, S = ( l / μA) is similar to resistance R = (ρl/A) in electric circuit.
  • Permeance (= 1/reluctance) in magnetic circuit is equivalent to conductance (=1/resistance) in electric circuit.

Differences between magnetic circuit and electric circuit


  • In magnetic circuit flux establishes but not flow like as current in magnetic circuit.
  • In magnetic circuit energy needed only to establish the flux but no consistent energy need to maintain it whereas in electric circuit continuous energy needed to flow of current.
  • Resistance of an electric circuit is constant (for same temperature) and is independent of current but reluctance of magnetic circuit is not constant because it depends on μ (=B/H) which is not constant and depends on B/H.

Shailendra Kumar Bhartee

Author: Shailendra Kumar Bhartee

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