Electrical Engineering ⇒ Topic : Electric and magnetic circuit

COMPARISON OF ELECTRIC AND MAGNETIC CIRCUITS

A series electric and magnetic circuits are shown in Fig. 1 (a) and (b) respectively.

Figure 1 (a) represents an electric circuit with three resistances connected in series, the dc source E drives the current I through all the three resistances whose voltage drops are V_I, V₂ and V_3. Hence, E = V₁ + V₂ + V₃, also E = I(R₁ + R₂ + R₃). We also know that  where ρ is the specific a resistance of the material, l is the length of the wire of the resistive material and a is the area of cross-section of the wire.

                                                                              FIGURE (1)

1/μ can be termed as reluctance of a cubic metre of magnetic material from which, the above equation gives the mmf per unit length (intensity) which is analogous to the voltage per unit length. Parallels between electric-circuit and magnetic-circuit quantities are shown in Table 

Thus, it is seen that the magnetic reluctance is analogous to resistance, mmf is analogous to emf and flux is analogous to current. These analogies are useful in magnetic circuit calculations. Though we can draw many parallels between the two circuits, the following differences do exists.

The electric current is a true flow but there is no flow in a magnetic flux. For a given temperature, ρ is independent of the strength of the current, but μ is not independent of the flux.

In an electric circuit energy is expended so long as the current flows, but in a magnetic circuit energy is expended only in creating the flux, and not in maintaining it.