WHAT ARE THE DIFFERENCES AND SIMILARITIES IN MAGNETIC AND ELECTRIC CIRCUITS?

Electrical and magnetic circuits behave in similar manner in several aspects. They share similar principles, laws and energy transfer mechanisms. These similarities make understanding and designing of magnetic circuits easier. Both circuits involve flow or transfer of energy (electrical or mechanical), flow of charge carriers (electric charges or magnetic domain).

Concept of magnetic circuit model, and its analogy with electrical circuit was developed around 1850-1890. It was based on lines similar to electrical circuits, as it was found the easiest way to deal and analyze magnetic circuits.

An electrical circuit consist of Electromotive Source (EMF), which produces electric field and the current. The current passes through resistances along its path and finally reaches back to the source in a closed loop. Magnitude of current is decided by resistances in this closed loop. Electric current is used to generate magnetic flux in ferromagnetic material, while a change in flux can produce an electric potential difference.

Electric field strength (or electric field intensity) E is the EMF per unit charge, measured in Volts/m. Magnetic field strength H is MMF per unit length, and has units of Ampere meter (Am). SI unit of current (I) is Ampere, while SI unit of flux (Ф) is Tesla or Weber. EMF(Volts) supplies energy to each unit of Coulomb charge, and maintains the potential difference (voltage). MMF is the pressure needed to establish the flux in ferromagnetic material. The figure below brings out striking similarities between electrical and magnetic circuits.

Similarities between magnetic and electric circuits

It will be interesting to go through the similarities in magnetic and electric circuits.

1. Driving Force: Electric current in electric circuit is driven by Electromotive Force (EMF), or Voltage, while Magnetomotive force (MMF) drives the flux in magnetic circuit. (Driving Force analogy)
2. Closed path: Both electric and magnetic circuits need a closed path- The start and end on the source (Voltage or MMF).
3. Definition of circuit: Path traced by charges in closed loop is electric current.  Path traced by flux is magnetic circuit.
4. Energy transfer: Resistances in electric circuit convert electrical energy into heat. Magnetic circuits store energy in magnetic field: minimum energy is needed to maintain flux.
5. Lines of force: Electric lines start at positive terminal and end on negative terminal. Magnetic lines start at North pole and end on South pole.
6. Circuit Laws: Kirchhoff’s Laws applies analogously in both circuits. KVL and KCL decide voltage and current in electric circuits. Sum of MMFs around a closed loop equal total applied MMF in magnetic circuit, and continuity of flux is maintained (Kirchhoff’s MMF law).
7. Opposition to flow: Resistances in electric circuit oppose the flow of current. Reluctance in magnetic circuit oppose the flux. Inverse of resistance is conductance, while inverse of reluctance is the permeance.
8. Series circuit:  Current in all elements of electric circuit is same.  Same flux passes through all elements in magnetic circuit.
9. Governing Law: Electric circuits obey Ohm’s Law V = IR. Magnetic circuits are governed by Hopkinson’s Law MMF = Flux х Reluctance

The analogies help in understanding and design of magnetic circuits and devices. However, these analogies apply only in linear region of magnetic devices. Non-linearities arise in magnetic circuits due to hysteresis, eddy currents, saturation, flux leakage and fringe effects.  

Electric and magnetic circuits have similarities in respect of driving forces, opposition, and energy transfer. However, the nature of flow, units, medium, and energy behavior are totally different. Understanding these similarities and differences is crucial for designing electrical devices that rely on both electric and magnetic phenomena.

Differences between magnetic and electric circuits

There are several basic differences between electric and magnetic circuits. These are as follows:

Feature	Electric circuit	Magnetic  circuit
Driving force	Electromotive force (V)	Magnetomotive force (MMF)
Flow entity	Electric current (A)	Magnetic flux (Wb)
Nature of flow	Electric charges	Magnetic dipole alignment. Flux sets up (does not flows like charges).
Medium	Conductors, can exist in vacuum	Magnetic materials
Opposition	Resistance (Ohms)	Reluctance (AT/Wb)
Insulation	Practically perfect insulators confine current	No perfect containment of flux. It can leak or fringe
Energy need	Needed for maintaining current	Needed to create flux, but not needed to maintain it.
Energy Dissipation	Continuous as heat	Energy to establish flux. Flux may leak or fringe outside